Subject: Gasoline FAQ - Part 2 of 4
Newsgroups: , rec.answers , news.answers

Archive-name: autos/gasoline-faq/part2
Posting-Frequency: monthly
Last-modified: 17 November 1996
Version: 1.12

4.12 Are brands different?

Yes. The above specifications are intended to ensure minimal quality 
standards are maintained, however as well as the fuel hydrocarbons, the 
manufacturers add their own special ingredients to provide additional 
benefits. A quality gasoline additive package would include:-
* octane-enhancing additives ( improve octane ratings )  
* anti-oxidants ( inhibit gum formation, improve stability ) 
* metal deactivators ( inhibit gum formation, improve stability )
* deposit modifiers ( reduce deposits, spark-plug fouling and 
  preignition )
* surfactants ( prevent icing, improve vaporisation, inhibit deposits,
  reduce NOx emissions ) 
* freezing point depressants ( prevent icing )
* corrosion inhibitors ( prevent gasoline corroding storage tanks ) 
* dyes ( product colour for safety or regulatory purposes ).
During the 1980s significant problems with deposits accumulating on intake 
valve surfaces occurred as new fuel injection systems were introduced. 
These intake valve deposits (IVD) were different than the injector deposits,
in part because the valve can reach 300C. Engine design changes that prevent 
deposits usually consist of ensuring the valve is flushed with liquid 
gasoline, and provision of adequate valve rotation. Gasoline factors that 
cause deposits are the presence of alcohols or olefins [46]. Gasoline 
manufacturers now routinely use additives that prevent IVD and also maintain 
the cleanliness of injectors. These usually include a surfactant and light 
oil to maintain the wetting of important surfaces. Intake valve deposits have 
also been shown to have significant adverse effects on emissions [47], and
deposit control additives will be required to both reduce emissions and 
provide clean engine operation [48]. A slighty more detailed description 
of additives is provided in Section 9.1.

Texaco demonstrated that a well-formulated package could improve fuel 
economy, reduce NOx emissions, and restore engine performance because, as 
well as the traditional liquid-phase deposit removal, some additives can 
work in the vapour phase to remove existing engine deposits without adversely 
affecting performance ( as happens when water is poured into a running engine 
to remove carbon deposits :-) )[49]. Chevron have also published data on the 
effectiveness of their additives [50], and successfully litigated to get 
Texaco to modify some of their claims [51]. Most suppliers of quality 
gasolines will formulate similar additives into their products, and cheaper 
product lines are less likely to have such additives added. As different 
brands of gasoline use different additives and oxygenates, it is probable 
that important fuel parameters, such as octane distribution, are slightly
different, even though the pump octane ratings are the same. 

So, if you know your car is well-tuned, and in good condition, but the
driveability is pathetic on the correct octane, try another brand. Remember 
that the composition will change with the season, so if you lose 
driveability, try yet another brand. As various Clean Air Act changes are 
introduced over the next few years, gasoline will continue to change.

4.13 What is a typical composition?

There seems to be a perception that all gasolines of one octane grade are
chemically similar, and thus general rules can be promulgated about "energy 
content ", "flame speed", "combustion temperature" etc. etc.. Nothing is 
further from the truth. The behaviour of manufactured gasolines in octane 
rating engines can be predicted, using previous octane ratings of special
blends intended to determine how a particular refinery stream responds to 
an octane-enhancing additive. Refiners can design and reconfigure refineries 
to efficiently produce a wide range of gasolines feedstocks, depending on
market and regulatory requirements. There is a worldwide trend to move to
unleaded gasolines, followed by the introduction of exhaust catalysts and 
sophisticated engine management systems. 

It is important to note that "oxygenated gasolines" have a hydrocarbon
fraction that is not too different to traditional gasolines, but that the
hydrocarbon fraction of "reformulated gasolines" ( which also contain 
oxygenates ) are significantly different to traditional gasolines.

The last 10 years of various compositional changes to gasolines for
environmental and health reasons have resulted in fuels that do not follow 
historical rules, and the regulations mapped out for the next decade also 
ensure the composition will remain in a state of flux. The reformulated
gasoline specifications, especially the 1/Jan/1998 Complex model, will
probably introduce major reductions in the distillation range, as well as
changing the various limits on composition and emissions.

I'm not going to list all 500+ HCs in gasolines, but the following are 
representative of the various classes typically present in a gasoline. The 
numbers after each chemical are:- Research Blending Octane : Motor Blending 
Octane : Boiling Point (C): Density (g/ml @ 15C) : Minimum Autoignition 
Temperature (C). It is important to realise that the Blending Octanes are 
derived from a 20% mix of the HC with a 60:40 iC8:nC7 ( 60 Octane Number )
base fuel, and the extrapolation of this 20% to 100%. These numbers result
from API Project 45, and are readily available. As modern refinery streams 
have higher base octanes, these Blending Octanes are higher than those 
typically used in modern refineries. For example, modern Blending Octane
ratings can be much lower ( toluene = 111RON and 94MON, 2-methyl-2-butene 
= 113RON and 81MON ), but detailed compilations are difficult to obtain. 

The technique for obtaining Blending Octanes is different from rating the 
pure fuel, which often requires adjustment of the test engine conditions 
outside the acceptable limits of the rating methods. Generally, the actual 
octanes of the pure fuel are similar for the alkanes, but are up to 30 
octane numbers lower than the API Project 45 Blending Octanes for the 
aromatics and olefins [52].   

A traditional composition I have dreamed up would be like the following, 
whereas newer oxygenated fuels reduce the aromatics and olefins, narrow the
boiling range, and add oxygenates up to about 12-15% to provide the octane.
The amount of aromatics in super unleaded fuels will vary greatly from
country to country, depending on the configuration of the oil refineries 
and the use of oxygenates as octane enhancers. The US is reducing the levels 
of aromatics to 25% or lower for environmental and human health reasons.

Some countries are increasing the level of aromatics to 50% or higher in 
super unleaded grades, usually to avoid refinery reconfiguration costs or
the introduction of oxygenates as they phase out the toxic lead octane
enhancers. An upper limit is usually placed on the amount of benzene
permitted, as it is known human carcinogen.

15% n-paraffins                       RON   MON    BP      d     AIT  
        n-butane                      113 : 114 :  -0.5:  gas  : 370
        n-pentane                      62 :  66 :  35  : 0.626 : 260
        n-hexane                       19 :  22 :  69  : 0.659 : 225
        n-heptane (0:0 by definition)   0 :   0 :  98  : 0.684 : 225
        n-octane                      -18 : -16 : 126  : 0.703 : 220
     ( you would not want to have the following alkanes in gasoline, 
       so you would never blend kerosine with gasoline )
        n-decane                      -41 : -38 : 174  : 0.730 : 210
        n-dodecane                    -88 : -90 : 216  : 0.750 : 204
        n-tetradecane                 -90 : -99 : 253  : 0.763 : 200
30%  iso-paraffins  
        2-methylpropane               122 : 120 : -12  :  gas  : 460
        2-methylbutane                100 : 104 :  28  : 0.620 : 420
        2-methylpentane                82 :  78 :  62  : 0.653 : 306
        3-methylpentane                86 :  80 :  64  : 0.664 :  -
        2-methylhexane                 40 :  42 :  90  : 0.679 : 
        3-methylhexane                 56 :  57 :  91  : 0.687 :
        2,2-dimethylpentane            89 :  93 :  79  : 0.674 :
        2,2,3-trimethylbutane         112 : 112 :  81  : 0.690 : 420
        2,2,4-trimethylpentane        100 : 100 :  98  : 0.692 : 415
          ( 100:100 by definition )
12% cycloparaffins 
        cyclopentane                  141 : 141 :  50  : 0.751 : 380
        methylcyclopentane            107 :  99 :  72  : 0.749 : 
        cyclohexane                   110 :  97 :  81  : 0.779 : 245
        methylcyclohexane             104 :  84 : 101  : 0.770 : 250
35% aromatics        
        benzene                        98 :  91 :  80  : 0.874 : 560
        toluene                       124 : 112 : 111  : 0.867 : 480
        ethyl benzene                 124 : 107 : 136  : 0.867 : 430
        meta-xylene                   162 : 124 : 138  : 0.868 : 463
        para-xylene                   155 : 126 : 138  : 0.866 : 530
        ortho-xylene                  126 : 102 : 144  : 0.870 : 530
        3-ethyltoluene                162 : 138 : 158  : 0.865 : 
        1,3,5-trimethylbenzene        170 : 136 : 163  : 0.864 : 
        1,2,4-trimethylbenzene        148 : 124 : 168  : 0.889 :
8% olefins               
        2-pentene                     154 : 138 :  37  : 0.649 :
        2-methylbutene-2              176 : 140 :  36  : 0.662 :
        2-methylpentene-2             159 : 148 :  67  : 0.690 :
        cyclopentene                  171 : 126 :  44  : 0.774 :
    ( the following olefins are not present in significant amounts
      in gasoline, but have some of the highest blending octanes )   
        1-methylcyclopentene          184 : 146 :  75  : 0.780 :
        1,3 cyclopentadiene           218 : 149 :  42  : 0.805 :
        dicyclopentadiene             229 : 167 : 170  : 1.071 :     

Published octane values vary a lot because the rating conditions are 
significantly different to standard conditions, for example the API Project 
45 numbers used above for the hydrocarbons, reported in 1957, gave MTBE 
blending RON as 148 and MON as 146, however that was partly based on the 
lead response, whereas today we use MTBE in place of lead.
        methanol                      133 : 105 :  65  : 0.796 : 385
        ethanol                       129 : 102 :  78  : 0.794 : 365
        iso propyl alcohol            118 :  98 :  82  : 0.790 : 399
        methyl tertiary butyl ether   116 : 103 :  55  : 0.745 : 
        ethyl tertiary butyl ether    118 : 102 :  72  : 0.745 :
        tertiary amyl methyl ether    111 :  98 :  86  : 0.776 : 
There are some other properties of oxygenates that have to be considered
when they are going to be used as fuels, particularly their ability to
form very volatile azeotropes that cause the fuel's vapour pressure to
increase, the chemical nature of the emissions, and their tendency to 
separate into a separate water-oxygenate phase when water is present. 
The reformulated gasolines address these problems more successfully than 
the original oxygenated gasolines.

Before you rush out to make a highly aromatic or olefinic gasoline to 
produce a high octane fuel, remember they have other adverse properties, 
eg the aromatics attack elastomers, may generate smoke, and result in
increased emissions of toxic benzene. The olefins are unstable ( besides 
smelling foul ) and form gums. The art of correctly formulating a gasoline 
that does not cause engines to knock apart, does not cause vapour lock in 
summer - but is easy to start in winter, does not form gums and deposits, 
burns cleanly without soot or residues, and does not dissolve or poison the 
car catalyst or owner, is based on knowledge of the gasoline composition.

4.14 Is gasoline toxic or carcinogenic? 

There are several known toxins in gasoline, some of which are confirmed
human carcinogens. The most famous of these toxins are lead and benzene, and 
both are regulated. The other aromatics and some toxic olefins are also 
controlled. Lead alkyls also require ethylene dibromide and/or ethylene 
dichloride scavengers to be added to the gasoline, both of which are 
suspected human carcinogens. In 1993 an International Symposium on the Health
Effects of Gasoline was held [53]. Major review papers on the carcinogenic,
neurotoxic, reproductive and developmental toxicity of gasoline, additives,
and oxygenates were presented, and interested readers should obtain the
proceedings. The oxygenates are also being evaluated for carcinogenicity, and 
even ethanol and ETBE may be carcinogens. The introduction of oxygenated
gasoline to Alaska and some other areas of the USA resulted in a range of
complaints. Recent research has been unable to identify additional toxicity,
but has detected increased levels of offensive smell [54]. It should be noted 
that the oxygenated gasolines were not initially intended to reduce the 
toxicity of emissions. The reformulated gasolines will produce different 
emissions, and specific toxins must initially be reduced by 15% all year.

The removal of alkyl lead compounds certainly reduces the toxicity of 
exhaust gas emissions when used on engines with modern engine management
systems and 3-way exhaust catalysts. If unleaded gasolines are not 
accompanied by the introduction of catalysts, some other toxic emissions
may increase. Engines without catalysts will produce increased levels of
toxic carbonyls such as formaldehyde and acrolein when using oxygenated
fuels, and increased levels of toxic benzene when using highly aromatic 

There is little doubt that gasoline is full of toxic chemicals, and should
therefore be treated with respect. However the biggest danger remains the 
flammability, and the relative hazards should always be kept in perspective. 
The major toxic risk from gasolines comes from breathing the tailpipe, 
evaporative, and refuelling emissions, rather than occasional skin contact 
from spills. Breathing vapours and skin contact should always be minimised.

4.15 Is unleaded gasoline more toxic than leaded?

The short answer is no. However that answer is not global, as some countries 
have replaced the lead compound octane-improvers with aromatic or olefin
octane-improvers without introducing exhaust catalysts. The aromatics
contents may increase to around 40%, with high octane unleaded fuels reaching 
50% in countries where oxygenates are not being used, and the producers have 
not reconfigured refineries to produce high octane paraffins. In general, 
aromatics are significantly more toxic than paraffins. Exhaust catalysts  
have a limited operational life, and will be immediately poisoned if 
misfuelled with leaded fuel. Catalyst failure can result in higher levels of
toxic emissions if catalysts or engine management systems are not replaced or
repaired when defective. Maximum benefit of the switch to unleaded are
obtained when the introduction of unleaded is accompanied by the introduction
of exhaust catalysts and sophisticated engine management systems.

Unfortunately, the manufacturers of alkyl lead compounds have embarked on a 
worldwide misinformation campaign in countries considering emulating the 
lead-free US. The use of lead precludes the use of exhaust catalysts, thus 
the emissions of aromatics are only slightly diminished, as leaded fuels
typically contain around 30-40% aromatics. Other toxins and pollutants that 
are usually reduced by exhaust catalysts will be emitted at significantly 
higher levels if leaded fuels are used [55]. 

The use of unleaded on modern vehicles with engine management systems and 
catalysts can reduce aromatic emissions to 10% of the level of vehicles 
without catalysts [55]. Alkyl lead additives can only substitute for some of 
the aromatics in gasoline, consequently they do not eliminate aromatics,
which will produce benzene emissions [56]. Alkyl lead additives also require 
toxic organohalogen scavengers, which also react in the engine to form and 
emit other organohalogens, including highly toxic dioxin [57]. Leaded fuels 
emit lead, organohalogens, and much higher levels of regulated toxins 
because they preclude the use of exhaust catalysts. In the USA the gasoline
composition is being changed to reduce fuel toxins ( olefins, aromatics ) 
as well as emissions of specific toxins. 

4.16 Is reformulated gasoline more toxic than unleaded?

The evidence so far indicates that the components of reformulated gasolines
( RFGs ) are more benign than unleaded, and that the tailpipe emissions of 
hydrocarbons are significantly reduced for cars without catalysts, and 
slightly reduced for cars with catalysts and engine management systems. The
emissions of toxic carbonyls such as formaldehyde, acetaldehyde and acrolein 
are increased slightly on all vehicles, and the emission of MTBE is increased
about 10x on cars without catalysts and 4x on cars with catalysts [55].
When all the emissions ( evaporative and tailpipe ) are considered, RFGs
significantly reduce emissions of hydrocarbons, however the emissions of
carbonyls and MTBE may increase [55]. There has been an extensive series
of reports on the emissions from RFGs, produced by the Auto/Oil Air Quality 
Improvement Research Program, who measured and calculated the likely
effects of RFG [18,19,20,58,59,60,61]. More research is required before 
a definitive answer on toxicity is available.  

The major question about RFGs is not the toxicity of the emissions, but 
whether they actually meet their objective of reducing urban pollution.
This is a more complex issue, and most experts agree the benefits will only
be modest [18,19,20,61,62]. 

4.17 Are all oxygenated gasolines also reformulated gasolines?

No. Oxygenates were initially introduced as alternative octane-enhancers in 
the 1930s, and are still used in some countries for that purpose. 
In the US the original "oxygenated gasolines" usually had a slightly-
modified gasoline as the hydrocarbon fraction. The US EPA also mandated 
their use to reduce pollution, mainly via the "enleanment" effect on engines 
without sophisticated management systems, but also because of the "aromatics 
substitution" effect. As vehicles with fuel injection and sophisticated 
engine management systems became pervasive, reformulated gasolines could be 
introduced to further reduce pollution. The hydrocarbon component of RFGs is 
significantly different to the hydrocarbon fraction in earlier oxygenated 
gasolines, having lower aromatics contents, reduced vapour pressure, and a 
narrower boiling range. RFGs do contain oxygenates as the octane-enhancer, 
but have different hydrocarbon composition profiles [34,41,42,43,44].


Subject: 5. Why is Gasoline Composition Changing?

5.1  Why pick on cars and gasoline? 

Cars emit several pollutants as combustion products out the tailpipe,
(tailpipe emissions), and as losses due to evaporation (evaporative 
emissions, refuelling emissions). The volatile organic carbon (VOC) 
emissions from these sources, along with nitrogen oxides (NOx) emissions 
from the tailpipe, will react in the presence of ultraviolet (UV) light
(wavelengths of less than 430nm) to form ground-level (tropospheric) ozone, 
which is one of the major components of photochemical smog [63]. Smog has 
been a major pollution problem ever since coal-fired power stations were 
developed in urban areas, but their emissions are being cleaned up. Now it's 
the turn of the automobile.

Cars currently use gasoline that is derived from fossil fuels, thus when 
gasoline is burned to completion, it produces additional CO2 that is added 
to the atmospheric burden. The effect of the additional CO2 on the global 
environment is not known, but the quantity of man-made emissions of fossil 
fuels must cause the system to move to a new equilibrium. Even if current 
research doubles the efficiency of the IC engine-gasoline combination, and 
reduces HC, CO, NOx, SOx, VOCs, particulates, and carbonyls, the amount of 
carbon dioxide from the use of fossil fuels may still cause global warming. 
More and more scientific evidence is accumulating that warming is occurring 
[64,65]. The issue is whether it is natural, or induced by human activities
and and a large panel of scientific experts continues to review scientific 
data and models. Interested reader should seek out the various publications
of the Intergovernmental Panel on Climate Change (IPCC). There are 
international agreements to limit CO2 emissions to 1990 levels, a target that 
will require more efficient, lighter, or appropriately-sized vehicles, - if 
we are to maintain the current usage. One option is to use "renewable" fuels 
in place of fossil fuels. Consider the amount of energy-related CO2 emissions 
for selected countries in 1990 [66].

                              CO2 Emissions
                         ( tonnes/year/person )
USA                               20.0
Canada                            16.4
Australia                         15.9
Germany                           10.4
United Kingdom                     8.6
Japan                              7.7
New Zealand                        7.6 
The number of new vehicles provides an indication of the magnitude of the
problem. Although vehicle engines are becoming more efficient, the distance
travelled is increasing, resulting in a gradual increase of gasoline 
consumption. The world production of vehicles (in thousands) over the last 
few years was [67];-


Region                       1990      1991     1992     1993     1994

Africa                        222       213      194      201      209
Asia-Pacific               12,064    12,112   11,869   11,463   11,020
Central & South America       800       888    1,158    1,523    1,727
Eastern Europe              2,466       984    1,726    1,837    1,547
Middle East                    35        24      300      390      274
North America               7,762     7,230    7,470    8,172    8,661
Western Europe             13,688    13,286   13,097   11,141   12,851
Total World                37,039    34,739   35,815   34,721   36,289

Trucks ( including heavy trucks and buses )

Region                       1990      1991     1992     1993     1994

Africa                        133       123      108      101      116
Asia-Pacific                5,101     5,074    5,117    5,057    5,407
Central & South America       312       327      351      431      457
Eastern Europe                980       776      710      600      244
Middle East                    36        28      100      128       76
North America               4,851     4,554    5,371    6,037    7,040
Western Europe              1,924     1,818    1,869    1,718    2,116
Total World                13,336    12,701   13,627   14,073   15,457

To fuel all operating vehicles, considerable quantities of gasoline
and diesel have to be consumed. Major consumption in 1994 of gasoline 
and middle distillates ( which may include some heating fuels, but
not fuel oils ) in million tonnes.

                             Gasoline    Middle Distillates
USA                           338.6            246.3
Canada                         26.8             26.1
Western Europe                163.2            266.8
Japan                          60.2             92.2
Total World                   820.4           1029.0

The USA consumption of gasoline increased from 294.4 (1982) to 335.6 (1989)
then dipped to 324.2 (1991), and has continued to rise since then to reach 
338.6 million tonnes in 1994. In 1994 the total world production of crude oil
was 3209.1 million tonnes, of which the USA consumed 807.9 million tonnes 
[68]. Transport is a very significant user of crude oil products, thus 
improving the efficiency of utilisation, and minimising pollution from 
vehicles, can produce immediate reductions in emissions of CO2, HCs, VOCs, 
CO, NOx, carbonyls, and other chemicals. 

5.2  Why are there seasonal changes?

Only gaseous hydrocarbons burn, consequently if the air is cold, then the 
fuel has to be very volatile. But when summer comes, a volatile fuel can 
boil and cause vapour lock, as well as producing high levels of evaporative 
emissions. The solution was to adjust the volatility of the fuel according 
to altitude and ambient temperature. This volatility change has been 
automatically performed for decades by the oil companies without informing 
the public of the changes. It is one reason why storage of gasoline through 
seasons is not a good idea. Gasoline volatility is being reduced as modern 
engines, with their fuel injection and management systems, can automatically 
compensate for some of the changes in ambient conditions - such as altitude 
and air temperature, resulting in acceptable driveability using less volatile

5.3  Why were alkyl lead compounds removed?

" With the exception of one premium gasoline marketed on the east coast
and southern areas of the US, all automotive gasolines from the mid-1920s
until 1970 contained lead antiknock compounds to increase antiknock quality. 
Because lead antiknock compounds were found to be detrimental to the 
performance of catalytic emission control system then under development, 
U.S. passenger car manufacturers in 1971 began to build engines designed to 
operate satisfactorily on gasolines of nominal 91 Research Octane Number. 
Some of these engines were designed to operate on unleaded fuel while others
required leaded fuel or the occasional use of leaded fuel. The 91 RON was 
chosen in the belief that unleaded gasoline at this level could be made 
available in quantities required using then current refinery processing
equipment. Accordingly, unleaded and low-lead gasolines were introduced 
during 1970 to supplement the conventional gasolines already available.

Beginning with the 1975 model year, most new car models were equipped
with catalytic exhaust treatment devices as one means of compliance with
the 1975 legal restrictions in the U.S. on automobile emissions. The need
for gasolines that would not adversely affect such catalytic devices has 
led to the large scale availability and growing use of unleaded gasolines,
with all late-model cars requiring unleaded gasoline."[69].

There was a further reason why alkyl lead compounds were subsequently 
reduced, and that was the growing recognition of the highly toxic nature of 
the emissions from a leaded-gasoline fuelled engine. Not only were toxic 
lead emissions produced, but the added toxic lead scavengers ( ethylene 
dibromide and ethylene dichloride ) could react with hydrocarbons to produce 
highly toxic organohalogen emissions such as dioxin. Even if catalysts were 
removed, or lead-tolerant catalysts discovered, alkyl lead compounds would 
remain banned because of their toxicity and toxic emissions [70,71].

5.4  Why are evaporative emissions a problem?

As tailpipe emissions are reduced due to improved exhaust emission control 
systems, the hydrocarbons produced by evaporation of the gasoline during 
distribution, vehicle refuelling, and from the vehicle, become more and
more significant. A recent European study found that 40% of man-made 
volatile organic compounds came from vehicles [72]. Many of the problem 
hydrocarbons are the aromatics and olefins that have relatively high octane 
values. Any sensible strategy to reduce smog and toxic emissions will also
attack evaporative and tailpipe emissions. 

The health risks to service station workers, who are continuously exposed 
to refuelling emissions remain a concern [73]. Vehicles will soon be 
required to trap the refuelling emissions in larger carbon canisters, as 
well as the normal evaporative emissions that they already capture. This 
recent decision went in favour of the oil companies, who were opposed by the 
auto companies. The automobile manufacturers felt the service station 
should trap the emissions. The activated carbon canisters adsorb organic
vapours, and these are subsequently desorbed from the canister and burnt in 
the engine during normal operation, once certain vehicle speeds and coolant
temperatures are reached. A few activated carbons used in older vehicles
do not function efficiently with oxygenates, but carbon cannister systems 
can reduce evaporative emissions by 95% from uncontrolled levels.

5.5  Why control tailpipe emissions?

Tailpipe emissions were responsible for the majority of pollutants in the 
late 1960s after the crankcase emissions had been controlled. Ozone levels 
in the Los Angeles basin reached 450-500ppb in the early 1970s, well above 
the typical background of 30-50ppb [74].

Tuning a carburetted engine can only have a marginal effect on pollutant 
levels, and there still had to be some frequent, but long-term, assessment 
of the state of tuning. Exhaust catalysts offered a post-engine solution 
that could ensure pollutants were converted to more benign compounds. As 
engine management systems and fuel injection systems have developed, the 
volatility properties of the gasoline have been tuned to minimise
evaporative emissions, and yet maintain low exhaust emissions.
The design of the engine can have very significant effects on the type and 
quantity of pollutants, eg unburned hydrocarbons in the exhaust originate 
mainly from combustion chamber crevices, such as the gap between the piston 
and cylinder wall, where the combustion flame can not completely use the HCs. 
The type and amount of unburnt hydrocarbon emissions are related to the fuel 
composition (volatility, olefins, aromatics, final boiling point), as well 
as state of tune, engine condition, and condition of the engine
lubricating oil [75]. Particulate emissions, especially the size fraction 
smaller than ten micrometres, are a serious health concern. The current 
major source is from compression ignition ( diesel ) engines, and the
modern SI engine system has no problem meeting regulatory requirements. 
The ability of reformulated gasolines to actually reduce smog has not yet 
been confirmed. The composition changes will reduce some compounds, and 
increase others, making predictions of environmental consequences extremely 
difficult. Planned future changes, such as the CAA 1/1/1998 Complex model 
specifications, that are based on several major ongoing government/industry 
gasoline and emission research programmes, are more likely to provide 
unambiguous environmental improvements. One of the major problems is the
nature of the ozone-forming reactions, which require several components 
( VOC, NOx, UV ) to be present. Vehicles can produce the first two, but the
their ratio is important, and can be affected by production from other 
natural ( VOC = terpenes from conifers ) or manmade ( NOx from power 
stations ) sources [62,63].  The regulations for tailpipe emissions 
will continue to become more stringent as countries try to minimise local 
problems ( smog, toxins etc.) and global problems ( CO2 ). Reformulation 
does not always lower all emissions, as evidenced by the following aldehydes 
from an engine with an adaptive learning management system [55].
                           FTP-weighted emission rates (mg/mi)
                                Gasoline      Reformulated
Formaldehyde                      4.87           8.43
Acetaldehyde                      3.07           4.71

The type of exhaust catalyst and management system can have significant
effects on the emissions [55].

                           FTP-weighted emission rates. (mg/mi)
                         Total Aromatics          Total Carbonyls
                     Gasoline  Reformulated    Gasoline  Reformulated
Noncatalyst          1292.45     1141.82        174.50     198.73
Oxidation Catalyst    168.60      150.79         67.08      76.94
3-way Catalyst        132.70       93.37         23.93      23.07
Adaptive Learning     111.69      105.96         17.31      22.35

If we take some compounds listed as toxics under the Clean Air Act, then the 
beneficial effects of catalysts are obvious. Note that hexane and iso-octane 
are the only alkanes listed as toxics, but benzene, toluene, ethyl benzene, 
o-xylene, m-xylene, and p-xylene are aromatics that are listed. The latter 
four are combined as C8 Aromatics below [55].
Aromatics               FTP-weighted emission rates. (mg/mi)
                      Benzene          Toluene        C8 Aromatics
                    Gas   Reform     Gas   Reform     Gas   Reform
Noncatalyst       156.18  138.48   338.36  314.14   425.84  380.44
Oxidation Cat.     27.57   25.01    51.00   44.13    52.27   47.07
3-way Catalyst     19.39   15.69    36.62   26.14    42.38   29.03
Adaptive Learn.    19.77   20.39    29.98   29.67    35.01   32.40

Aldehydes               FTP-weighted emission rates. (mg/mi)
                    Formaldehyde      Acrolein        Acetaldehyde
                    Gas   Reform     Gas   Reform     Gas   Reform
Noncatalyst        73.25   85.24    11.62   13.20    19.74   21.72
Oxidation Cat.     28.50   35.83     3.74    3.75    11.15   11.76
3-way Catalyst      7.27    7.61     1.11    0.74     4.43    3.64
Adaptive Learn.     4.87    8.43     0.81    1.16     3.07    4.71

Others              1,3 Butadiene       MTBE
                    Gas   Reform     Gas   Reform
Noncatalyst         2.96    1.81    10.50  130.30  
Oxidation Cat.      0.02    0.33     2.43   11.83
3-way Catalyst      0.07    0.05     1.42    4.59
Adaptive Learn.     0.00    0.14     0.84    3.16

The author reports analytical problems with the 1,3 Butadiene, and only
Noncatalyst values are considered reliable. Other studies from the
Auto/Oil research program indicate that lowering aromatics and olefins
reduce benzene but increase formaldehyde and acetaldehyde [20]  

Emission Standards

There are several bodies responsible for establishing standards, and they
promulgate test cycles, analysis procedures, and the % of new vehicles that 
must comply each year. The test cycles and procedures do change ( usually 
indicated by an anomalous increase in the numbers in the table ), and I 
have not listed the percentages of the vehicle fleet that are required to 
comply. This table is only intended to convey where we have been, and where 
we are going. It does not cover any regulation in detail - readers are 
advised to refer to the relevant regulations. Additional limits for other 
pollutants, such as formaldehyde (0.015g/mi.) and particulates (0.08g/mi), 
are omitted. The 1994 tests signal the federal transition from 50,000 to 
100,000 mile compliance testing, and I have not listed the subsequent 
50,000 mile limits [28,76,77].
Year                    Federal                      California
                HCs    CO    NOx    Evap       HCs    CO    NOx    Evap
               g/mi   g/mi  g/mi   g/test     g/mi   g/mi  g/mi   g/test
Before regs   10.6   84.0   4.1    47        10.6   84.0   4.1    47
add crankcase +4.1                           +4.1 
1966                                          6.3   51.0   6.0
1968           6.3   51.0   6.0
1970           4.1   34.0                     4.1   34.0           6
1971           4.1   34.0           6(CC)     4.1   34.0   4.0     6
1972           3.0   28.0           2         2.9   34.0   3.0     2
1973           3.0   28.0   3.0               2.9   34.0   3.0     2
1974           3.0   28.0   3.0               2.9   34.0   2.0     2
1975           1.5   15.0   3.1     2         0.90   9.0   2.0     2
1977           1.5   15.0   2.0     2         0.41   9.0   1.5     2
1980           0.41   7.0   2.0     6(SHED)   0.41   9.0   1.0     2
1981           0.41   3.4   1.0     2         0.39   7.0   0.7     2
1993           0.41   3.4   1.0     2         0.25   3.4   0.4     2
1994  50,000   0.26   3.4   0.3     2   TLEV  0.13   3.4   0.4     2 
1994 100,000   0.31   4.2   0.6     2
1997                                    LEV   0.08   3.4   0.2
1997                                    ULEV  0.04   1.7   0.2
1998                                    ZEV   0.0    0.0   0.0     0
2004           0.125  1.8   0.16    2

It's also worth noting that exhaust catalysts also emit platinum, and the
soluble platinum salts are some of the most potent sensitizers known.
Early research [78] reported the presence of 10% water-soluble platinum in 
the emissions, however later work on monolithic catalysts has determined the
quantities of water soluble platinum emissions are negligible [79]. The 
particle size of the emissions has also been determined, and the emissions 
have been correlated with increasing vehicle speed. Increasing speed also 
increases the exhaust gas temperature and velocity, indicating the emissions 
are probably a consequence of physical attrition.

           Estimated Fuel                           Median Aerodynamic
Speed       Consumption         Emissions           Particle Diameter
km/h          l/100km            ng/m-3                    um
60              7                  3.3                     5.1           
100             8                 11.9                     4.2
140            10                 39.0                     5.6
US Cycle-75                        6.4                     8.5

Using the estimated fuel consumption, and about 10m3 of exhaust gas per 
litre of gasoline, the emissions are 2-40 ng/km. These are 2-3 orders
of magnitude lower than earlier reported work on pelletised catalysts.
These emissions may be controlled directly in the future. They are currently 
indirectly controlled by the cost of platinum, and the new requirement for 
the catalyst to have an operational life of at least 100,000 miles.
5.6  Why do exhaust catalysts influence fuel composition?

Modern adaptive learning engine management systems control the combustion
stoichiometry by monitoring various ambient and engine parameters, including
exhaust gas recirculation rates, the air flow sensor, and exhaust oxygen 
sensor outputs. This closed loop system using the oxygen sensor can 
compensate for changes in fuel content and air density. The oxygen sensor
is also known as the lambda sensor because the actual air-fuel mass ratio 
divided by the stoichiometric air-fuel mass ratio is known as lambda or the
air-fuel equivalence ratio. 

The preferred technique for describing mixture strength is the fuel-air 
equivalence ratio ( phi ), which is the actual fuel-air mass ratio divided 
by the stoichiometric fuel-air mass ratio, however most enthusiasts use 
air-fuel ratio and lambda. Lambda is the inverse of the fuel-air equivalence 
ratio. The oxygen sensor effectively measures lambda around the 
stoichiometric mixture point. Typical stoichiometric air-fuel ratios are 
      6.4  methanol
      9.0  ethanol
     11.7  MTBE
     12.1  ETBE, TAME
     14.6  gasoline without oxygenates

The engine management system rapidly switches the stoichiometry between 
slightly rich and slightly lean, except under wide open throttle conditions 
- when the system runs open loop. The  response of the oxygen sensor to 
composition changes is about 3 ms, and closed loop switching is typically 
1-3 times a second, going between 50mV ( lambda = 1.05 (Lean)) to  900mV 
(lambda = 0.99 ( Rich)). The catalyst oxidises about 80% of the H2, CO, 
and HCs, and reduces the NOx [76]. 

Typical reactions that occur in a modern 3-way catalyst are:-
                2H2 + O2  ->  2H2O
                2CO + O2  ->  2CO2
    CxHy + (x + (y/4))O2  ->  xCO2 + (y/2)H2O
               2CO + 2NO  ->  N2 + 2CO2
   CxHy + 2(x + (y/4))NO  ->  (x + (y/4))N2 + (y/2)H2O + xCO2
               2H2 + 2NO  ->  N2 + 2H2O
                CO + H20  ->  CO2 + H2
             CxHy + xH2O  ->  xCO + (x + (y/2))H2          

The use of exhaust catalysts have resulted in reaction pathways that can 
accidentally be responsible for increased pollution. An example is the 
CARB-mandated reduction of fuel sulfur. A change from 450ppm to 50ppm, which 
will reduce HC & CO emissions by 20%, was shown to increase formaldehyde by 
45%, but testing in later model cars did not exhibit the same effect [32,58,
59]. This demonstrates that continuing changes to engine management systems
can also change the response to fuel composition changes.

The requirement that the exhaust catalysts must now endure for 10 years or 
100,000 miles will also encourage automakers to push for lower levels of 
elements that affect exhaust catalyst performance, such as sulfur and 
phosphorus, in both the gasoline and lubricant. Modern catalysts are unable 
to reduce the relatively high levels of NOx that are produced during lean 
operation down to approved levels, thus preventing the application of 
lean-burn engine technology. Recently Mazda has announced they have 
developed a "lean burn" catalyst, which may enable automakers to move the 
fuel combustion towards the lean side, and different gasoline properties may 
be required to optimise the combustion and reduce pollution [81]. Mazda 
claim that fuel efficiency is improved by 5-8%, while meeting all emission 
regulations, and some Japanese manufacturers have evaluated lean-burn 
catalysts in limited numbers of 1995 production models. 

Catalysts also inhibit the selection of gasoline octane-improving and 
cleanliness additives ( such as MMT and phosphorus-containing additives ) 
that may result in refractory compounds known to physically coat the 
catalyst, reducing available catalyst and thus increasing pollution. 

5.7  Why are "cold start" emissions so important?

The catalyst requires heat to reach the temperature ( >300-350C ) where it 
functions most efficiently, and the delay until it reaches operating 
temperature can produce more hydrocarbons than would be produced during 
the remainder of many typical urban short trips. It has been estimated that
70-80% of the non-methane HCs that escape conversion by the catalysts 
are emitted during the first two minutes after a cold start. As exhaust 
emissions have been reduced, the significance of the evaporative emissions 
increases. Several engineering techniques are being developed, including the 
Ford Exhaust Gas Igniter ( uses a flame to heat the catalyst - lots of 
potential problems ), zeolite hydrocarbon traps, and relocation of the
catalyst closer to the engine [76]. 

Reduced gasoline volatility and composition changes, along with cleanliness 
additives and engine management systems, can help minimise cold start 
emissions, but currently the most effective technique appears to be rapid, 
deliberate heating of the catalyst, and the new generation of low thermal 
inertia  "fast light-up" catalysts reduce the problem, but further research 
is necessary [76,82].

As the evaporative emissions are also starting to be reduced, the emphasis
has shifted to the refuelling emissions. These will be mainly controlled
on the vehicle, and larger canisters may be used to trap the vapours emitted
during refuelling. 

5.8  When will the emissions be "clean enough"?

The California ZEV regulations effectively preclude IC vehicles, because
they stipulate zero emissions. However, the concept of regulatory forcing
of alternative vehicle propulsion technology may have to be modified to
include hybrid or fuel-cell vehicles, as the major failing of EVs remains
the lack of a cheap, light, safe, and  easily-rechargeable electrical 
storage device [83,84]. There are several major projects intending to 
further reduce emissions from automobiles, mainly focusing on vehicle mass 
and engine fuel efficiency, but gasoline specifications and alternative 
fuels are also being investigated. It may be that changes to IC engines and 
gasolines will enable the IC engine to continue well into the 21st century 
as the prime motive force for personal transportation [77,85]. There have 
also been calls to use market forces to reduce pollution from automobiles 
[86], however most such suggestions ( increased gasoline taxes, congestion 
tolls, and emission-based registration fees ) are currently considered 
politically unacceptable. The issue of how to target the specific "gross 
polluters" is being considered, and is described in Section 5.14.

5.9  Why are only some gasoline compounds restricted?

The less volatile hydrocarbons in gasoline are not released in significant 
quantities during normal use, and the more volatile alkanes are considerably
less toxic than many other chemicals encountered daily. The newer gasoline 
additives also have potentially undesirable properties before they are even
combusted. Most hydrocarbons are very insoluble in water, with the lower
aromatics being the most soluble, however the addition of oxygen to 
hydrocarbons significantly increases the mutual solubility with water.

                      Compound in Water            Water in Compound       
                      % mass/mass @  C             % mass/mass @  C
normal decane            0.0000052  25               0.0072      25
iso-octane               0.00024    25               0.0055      20
normal hexane            0.00125    25               0.0111      20
cyclohexane              0.0055     25               0.010       20
1-hexene                 0.00697    25               0.0477      30
toluene                  0.0515     25               0.0334      25
benzene                  0.1791     25               0.0635      25

methanol                complete    25              complete     25
ethanol                 complete    25              complete     25 
MTBE                     4.8        20               1.4         20
TAME                      -                          0.6         20
The concentrations and ratios of benzene, toluene, ethyl benzene, and xylenes 
( BTEX ) in water are often used to monitor groundwater contamination from
gasoline storage tanks or pipelines. The oxygenates and other new additives 
may increase the extent of water and soil pollution by acting as co-solvents 
for HCs. 

Various government bodies ( EPA, OSHA, NIOSH ) are charged with ensuring
people are not exposed to unacceptable chemical hazards, and maintain
ongoing research into the toxicity of liquid gasoline contact, water and soil
pollution, evaporative emissions, and tailpipe emissions [87]. As toxicity 
is found, the quantities in gasoline of the specific chemical ( benzene ), 
or family of chemicals ( alkyl leads, aromatics, olefins ) are regulated.

The recent dramatic changes caused by the need to reduce alkyl leads,
halogens, olefins, and aromatics has resulted in whole new families of 
compounds ( ethers, alcohols ) being introduced into fuels without prior 
detailed toxicity studies being completed. If adverse results appear, these 
compounds are also likely to be regulated to protect people and the 

Also, as the chemistry of emissions is unravelled, the chemical precursors
to toxic tailpipe emissions ( such as higher aromatics that produce benzene  
emissions ) are also controlled, even if they are not themselves toxic.

5.10 What does "renewable" fuel or oxygenate mean?

The general definition of "renewable" is that the carbon originates from 
recent biomass, and thus does not contribute to the increased CO2 emissions. 
A truly "long-term" view could claim that fossil fuels are "renewable" on a
100 million year timescale :-). There was a major battle between the 
ethanol/ETBE lobby ( agricultural, corn growing ), and the methanol/MTBE 
lobby ( oil company, petrochemical ) over an EPA mandate demanding that a
specific percentage of the oxygenates in gasoline are produced from 
"renewable" sources [88]. On 28 April 1995 a Federal appeals court 
permanently voided the EPA ruling requiring "renewable" oxygenates, thus
fossil-fuel derived oxygenates such as MTBE are acceptable oxygenates [89]. 

Unfortunately, "renewable" ethanol is not cost competitive when crude oil 
is $18/bbl, so a federal subsidy ( $0.54/US Gallon ) and additional state 
subsidies ( 11 states - from $0.08(Michigan) to $0.66(Tenn.)/US Gal.) are 
provided. Ethanol, and ETBE derived from ethanol, are still likely to be 
used in states where subsidies make them competitive with other oxygenates. 

5.11 Will oxygenated gasoline damage my vehicle?

The following comments assume that your vehicle was designed to operate on 
unleaded, if not, then damage such as exhaust valve seat recession may occur. 
Damage should not occur if the gasoline is correctly formulated, and you 
select the appropriate octane, but oxygenated gasoline will hurt your pocket.
In the first year of mandated oxygenates, it appears some refiners did not 
carefully formulate their oxygenated gasoline, and driveability and emissions 
problems occurred. Most reputable brands are now carefully formulated. 
Some older activated carbon canisters may not function efficiently with
oxygenated gasolines, but this is a function of the type of carbon used.
How your vehicle responds to oxygenated gasoline depends on the engine 
management system and state of tune. A modern system will automatically 
compensate for all of the currently-permitted oxygenate levels, thus your
fuel consumption will increase. Older, poorly-maintained, engines may 
require a tune up to maintain acceptable driveability.

Be prepared to try several different brands of oxygenated or reformulated 
gasolines to identify the most suitable brand for your vehicle, and be 
prepared to change again with the seasons. This is because the refiners can 
choose the oxygenate they use to meet the regulations, and may choose to set 
some fuel properties, such as volatility, differently to their competitors. 

Most stories of corrosion etc, are derived from anhydrous methanol corrosion 
of light metals (aluminum, magnesium), however the addition of either 0.5% 
water to pure methanol, or corrosion inhibitors to methanol-gasoline blends 
will prevent this. If you observe corrosion, talk to your gasoline supplier.  
Oxygenated fuels may either swell or shrink some elastomers on older cars, 
depending on the aromatic and olefin content of the fuels. Cars later than 
1990 should not experience compatibility problems, and cars later than 1994 
should not experience driveability problems, but they will experience 
increased fuel consumption, depending on the state of tune and engine 
management system.  
5.12 What does "reactivity" of emissions mean?

The traditional method of exhaust regulations was to specify the actual HC, 
CO, NOx, and particulate contents. With the introduction of oxygenates and 
reformulated gasolines, the volatile organic carbon (VOC) species in the 
exhaust also changed. The "reactivity" refers to the ozone-forming potential 
of the VOC emissions when they react with NOx, and is being introduced as a 
regulatory means of ensuring that automobile emissions do actually reduce 
smog formation. The ozone-forming potential of chemicals is defined as the 
number of molecules of ozone formed per VOC carbon atom, and this is called 
the Incremental Reactivity. Typical values ( big is bad :-) ) are [74]: 

Maximum Incremental Reactivities as mg Ozone / mg VOC 

                  carbon monoxide           0.054
alkanes           methane                   0.0148
                  ethane                    0.25
                  propane                   0.48
                  n-butane                  1.02
olefins           ethylene                  7.29
                  propylene                 9.40
                  1,3 butadiene            10.89
aromatics         benzene                   0.42
                  toluene                   2.73
                  meta-xylene               8.15      
                  1,3,5-trimethyl benzene  10.12
oxygenates        methanol                  0.56
                  ethanol                   1.34
                  MTBE                      0.62
                  ETBE                      1.98

5.13 What are "carbonyl" compounds?

Carbonyls are produced in large amounts under lean operating conditions,
especially when oxygenated fuels are used. Most carbonyls are toxic, and the 
carboxylic acids can corrode metals. The emission of carbonyls can be 
controlled by combustion stoichiometry and exhaust catalysts, refer to
section 5.5 for typical reductions for aldehydes.  
Typical carbonyls are:-
* aldehydes ( containing -CHO ),
  - formaldehyde (HCHO) - which is formed in large amounts during lean 
                          combustion of methanol [90].
  - acetaldehyde (CH2CHO) - which is formed during ethanol combustion. 
  - acrolein (CH2=CHCHO) - a very potent irritant and toxin.
* ketones ( containing C=0 ),
  - acetone (CH3COCH3)
* carboxylic acids ( containing -COOH ),
  - formic acid (HCOOH) - formed during lean methanol combustion. 
  - acetic acid (CH3COOH). 

5.14 What are "gross polluters"? 

It has always been known that the EPA emissions tests do not reflect real 
world conditions. There have been several attempts to identify vehicles on 
the road that do not comply with emissions standards. Recent remote sensing 
surveys have demonstrated that the highest 10% of CO emitters produce over 
50% of the pollution, and the same ratio applies for the HC emitters 
- which may not be the same vehicles [91-102]. 20% of the CO emitters are 
responsible for 80% of the CO emissions, consequently modifying gasoline 
composition is only one aspect of pollution reduction. The new additives can 
help maintain engine condition, but they can not compensate for out-of-tune,
worn, or tampered-with engines. There has recently been some unpublished
studies that demonstrate that the current generation of remote sensing
systems can not provide sufficient discrimination of gross polluters without
also producing false positives for some acception vehicles - more work
is required, and in some states I&M emissions testing using dynamometers
is being introduced to identify gross polluters.

The most famous of the remote sensing systems is the FEAT ( Fuel Efficiency 
Automobile Test ) team from the University of Denver [99]. This team is 
probably the world leader in remote sensing of auto emissions to identify 
grossly polluting vehicles. The system measures CO/CO2 ratio, and the 
HC/CO2 ratio in the exhaust of vehicles passing through an infra-red light 
beam crossing the road 25cm above the surface. The system also includes a 
video system that records the licence plate, date, time, calculated exhaust 
CO, CO2, and HC. The system is effective for traffic lanes up to 18 metres
wide, however rain, snow, and water spray can cause scattering of the beam.
Reference signals monitor such effects and, if possible, compensate. The
system has been comprehensively validated, including using vehicles with 
on-board emissions monitoring instruments.

They can monitor up to 1000 vehicles an hour and, as an example,they were 
invited to Provo, Utah to monitor vehicles, and gross polluters would be 
offered free repairs [100]. They monitored over 10,000 vehicles and mailed 
114 letters to owners of vehicles newer than 1965 that had demonstrated high 
CO levels. They received 52 responses and repairs started in Dec. 1991, and 
continued to Mar 1992. 

 The entire monitored fleet at Provo (Utah) during Winter 1991:1992 
 Model year               Grams CO/gallon            Number of
                    (Median value) (mean value)      Vehicles
   92                    40             80              247
   91                    55                            1222
   90                    75                            1467
   89                    80                            1512
   88                    85                            1651
   87                    90                            1439
   86                   100            300             1563
   85                   120                            1575
   84                   125                            1206
   83                   145                             719
   82                   170                             639
   81                   230                             612
   80                   220            500              551
   79                   350                             667
   78                   420                             584
   77                   430                             430
   76                   770                             317
   75                   760            950              163
   Pre 75               920           1060              878

As observed elsewhere, over half the CO was emitted by about 10% of the 
vehicles. If the 47 worst polluting vehicles were removed, that achieves 
more than removing the 2,500 lowest emitting vehicles from the total tested 

Surveys of vehicle populations have demonstrated that emissions systems had 
been tampered with on over 40% of the gross polluters, and an additional 20% 
had defective emission control equipment [101]. No matter what changes are 
made to gasoline, if owners "tune" their engines for power, then the majority
of such "tuned" vehicle will become gross polluters. Professional repairs to 
gross polluters usually improves fuel consumption, resulting in a low cost to
owners ( $32/pa/Ton CO year ). The removal of CO in the Provo example above 
was costed at $200/Ton CO, compared to Inspection and Maintenance programs 
($780/Ton CO ), and oxygenates ( $1034-$1264/Ton CO in Colorado 1991-2 ), and
UNOCALs vehicle scrapping programme ( $1025/Ton of all pollutants ).

Thus, identifying and repairing or removing gross polluters can be far more 
cost-effective than playing around with reformulated gasolines and 
oxygenates. A recent study has confirmed that gross polluters are not always
older vehicles, and that vehicles have been scrapped that passed the 1993 new
vehicle emission standards [102]. The study also confirmed that if estimated
costs and benefits of various emission reduction strategies were applied to
the tested fleet, the identification and repair techniques are the most 
cost-effective means of reducing HC and CO. It should be noted that some 
strategies ( such as the use of oxygenates to replace aromatics and alkyl 
lead compounds ) have other environmental benefits. 

Action                      Vehicles   Estimated  % reduction  % reduction 
                            Affected     Cost                  per $billion
                           (millions) ($billion)   HC    CO     HC    CO
Reformulated Fuels            20         1.5       17    11     11     7.3
Scrap pre-1980 vehicles        3.2       2.2       33    42     15    19
Scrap pre-1988 vehicles       14.6      17         44    67      2.6   3.9
Repair worst 20% of vehicles   4         0.88      50    61     57     69
Repair worst 40% of vehicles   8         1.76      68    83     39     47





 [  Back to John's Octane Page ]

Updated: 2/27/2007