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rmay635703 -

Originally Posted by rmay635703

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Its too bad lean burn couldn't be LEGAL in areas where it would not affect the air quality (aka rural) with our level of tech I would think even the government could make a system so the cars emissions could run within the required limits of the region or city. Lean burn could definately reduce our overall use of gas.

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The issue that this article talks about got me thinking :

The Ozone Weekend Effect — UC Berkeley College of Engineering - March 2009

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This puzzling exception is known as the ozone weekend effect. In many urban areas, tailpipe emissions of NOx are lower on weekends because the roads carry less diesel truck traffic on those days. This translates into lower levels of airborne soot on Saturday and Sunday and lower levels of secondary pollutants like ammonium nitrate on Sunday and Monday. (There's a one-day “chemistry delay” as NOx, ammonia and other chemicals in the air react to form their smoggy end-products.) But for ozone, the levels are often higher on weekends, when NOx emissions are lower.

Ozone is the poster chemical for air pollution, linked to many respiratory illnesses. There are two main ways to control ozone: either reduce NOx emissions; or reduce levels of volatile organic compounds (VOCs) such as evaporated gas, cleaning product hydrocarbons and methane (responsible for the current controversy over a possible “cow tax” on farmers). NOx emissions have dropped steadily over the past 15 years, thanks to cleaner car engines. And, ever since people in the air quality field began observing the ozone weekend effect, some have wondered whether continued NOx reductions might actually be counterproductive. “There's a big debate,” Harley explains. “Some people say, ‘We don't want to do more NOx control. We should focus on the other precursors to ozone.’”

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By examining the chemistry of ozone formation, Harley found that ozone is generated most readily in air that has a mass ratio of 2.4 parts VOC to 1 part NOx. If the NOx levels are higher than this, reducing them just slightly—as happens on weekends when diesel traffic is reduced—can actually elevate the ozone level. This explains the ozone weekend effect. But if you reduce NOx levels significantly below that ratio, ozone production falls rapidly. On a 3-D graph, it's like having to go over a ridge to make it down to the low areas. Harley argues that, because much of the VOC content in the air now comes from natural sources like vegetation, further reduction of NOx is the best way to reduce ozone.

In terms of policy, this argument has now prevailed, and diesel is the new target for emissions standards. Nationally, all new diesel engines with model year 2007 and later are equipped with particle filters to reduce soot and other particulates. California law will likely be stricter: the state's Air Resources Board is set to pass a rule requiring all older trucks that operate in California to be retrofitted with particle filters (or have their engines replaced) by 2012, and, by 2023, to add catalytic converters for NOx control. Roughly one million existing trucks would be subject to these requirements.

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Let's say for the point of argument that emissions-sensor equipment is dirt cheap. In that situation you could have on-board emissions sensors dedicated to sampling the *external* atmosphere. In that situation the ECU/PCM could calculate that it is beneficial to "go lean" under certain atmospheric conditions.

CarloSW2