Expert: Harold Garabedian - 4/16/2001

Question
Dear Harold: I hope you can help me to clarify - very briefly, only a few lines - on the following three points:
1.- Which are the (dis) advantages, specially regarding health and environment, between leaded and unleaded gas?
2.- Is it true that the making of unleaded gas is simpler and, therefore, should also be cheaper, as is the case in most countries that sell both types of gas?
3.- Will a car built to work with leaded gas perform as well if loaded with unleaded gas? or: must motor cars of leaded gas that switch to unleaded gas need changes in their motor, so as to work adequately?
Can you help me with these questions? Best regards. Rolando Stein.


Answer
Dear Rolando --

I hope you find the following helpful.

1.- Which are the (dis) advantages, specially regarding health and environment, between leaded and unleaded gas?

Gasoline in general is a very hazardous and toxic product.  As a society we have become (too) comfortable with these threats.  

The production and consumption of leaded and unleaded gasoline represent significant threats to public health.  Lead is human toxin and can impede normal development, nero-development is particularly sensitive to the ill-effects of lead.  Lead also bio-accumulates (doesn't go away) in the environment and can be toxic to the aquatic and terrestrial biota.  

The hazard of unleaded gasoline are the same as leaded gas, without the lead.  These concerns fall into two general problems; smog formation and air toxics.  Gasoline is major source of hydrocarbon compounds into the environment, either through evaporation or incomplete combustion.  Hydrocarbons, together with nitrogen oxides in the presence of sunlight can form photochemical oxidants, or smog.  Over half the nations population live in areas of the country whose air quality does not meet the national health standard for smog.  Gasoline is comprised of over two hundred chemicals, most of which are toxic or hazardous and some are carcinogenic.

Lead was first taken out of gasoline in the mid-1970s in the US so that catalysts could be installed on motor vehicle to control tailpipe emissions.  The lead needed to be removed so as not to poison the catalyst and render it inoperative.  During the same period of time a national health-based air quality standard for lead was established.  This further the removal of lead from gasoline. National lead level in outdoor have decreased some 90+% from this period and human blood level levels (in the US) have fallen as well.  More about lead in the environment can be learned form the US Environmental Protection Agency's web site (www.epa.gov).


2.- Is it true that the making of unleaded gas is simpler and, therefore, should also be cheaper, as is the case in most countries that sell both types of gas?

Lead was added to gasoline as a cheap way to increase the anti-knock property of gasoline (increase octane rating).  With the removal of lead, refineries had to achieve octane through other means.  In the 1980s as the demand for unleaded gasoline increased (a greater proportion of the cars on the road were fitted with catalysts), refineries achieved octane by blending in more lighter end hydrocarbon stock.  This material was readily available as a result of increasing natural gas production. While this did achieve the requisite octane, it increased the volatility of gasoline, that is it evaporated more readily. This had the undue effect of greater hydrocarbon emissions overall, with these emissions occurring throughout the production, and handling and use of gasoline.  These greater emissions exacerbated smog levels, particularly along the eastern coast of the nation.  With the establishment of volatility limits on gasoline, the refiners produced gasoline that was not only unleaded, yet met volatility limits.  To do this required large physical modifications to the refining process and greater refining of petroleum stocks.  These modifications produced complying fuels, but with lower yields of base stocks. Those lower yields is what drove price up despite the fact an additive (lead) was removed.

3.- Will a car built to work with leaded gas perform as well if loaded with unleaded gas? or: must motor cars of leaded gas that switch to unleaded gas need changes in their motor, so as to work adequately?

An old technology engines can operate on unleaded gasoline, however there can be a  a risk of burning out the exhaust valves of old technology engines if operated with unleaded gasoline in heavy constant service (emphasis on heavy constant service). This is because old technology engines relied upon the lead in the gasoline to coat and protect exhaust valves from the extreme heat of the exhaust. I believe this risk is minor.  I personally have been operating a 35 year old snow blower on unleaded gasoline for over twenty years with no problem. The one remaining use of leaded gasoline in the US in is in aviation gasoline.  This has been justified on the proportion of old technology engine remaining in use and when operated are operated at near full throttle constantly.

Leaded gasoline is virtually non-existent in the US and all gasoline powered passenger cars and trucks are fitted with engines designed to operate on unleaded gasoline.  Harm can be done if these engines are operated on leaded gasoline.

-- Harold Garabedian