Today is a “Spare the Air” day in Silicon Valley so it seems like a good day to look at the environmental consequences of different car choices. One of the reasons to choose green transportation is potential environmental improvements. Spare the Air days are issued by the Bay Area Air Quality Management District on days for which the Air Quality Index (AQI) is forecast to be unhealthy. The AQI only includes the federal air quality standards for six major pollutants – ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, and two sizes of particulate matter. Recall that during the Bush Administration years there was debate over whether CO2 is a pollutant, making CO2 a conspicuous absence from this list.
They offer 10 clean air tips all of which involves driving less to use less gasoline. Drive less, take public transit, carpooling, telecommuting, etc. In the SF Bay Area the major sources of air pollution are the mobile vehicles, transportation. All mobile sources account for 194 tons per day of volatile organic compounds, and 431 tons per day of nitrogen oxides (NOx). Of that cars and light duty trucks account for 101 tons and 95 tons respectively. By comparison “man made stationary sources” account for only 183 and 74 tons respectively. The total pollutants are 377 tons volatile organic compounds, and 505 tons of NOx. Percentage-wise mobile sources (transportation) are the source of 51% of volatile organic compounds (cars and light trucks 27%) and 85% of NOx (18%). The biggest source of NOx is heavy trucks, buses and motorcycles (32%).
Clearly for the air pollution in the SF Bay Area low pollution vehicles would make a positive benefit.
During the summer months it is “ground-level ozone” (a.k.a. smog) which is the major concern. Unlike high level ozone (which is beneficial) ozone at the ground level is unhealthy and unhelpful. Ground level ozone is invisible and the brown haze we see is instead NOx. In the SF Bay Area there is also a lot of mist (a.k.a. small particles of water vapor) on many days, and that mist causes some of the murkyness in our air. Water vapor is natural and not a health or environmental problem, unlike the ozone and NOx.
During the summer months the major concern is instead “particulates”. Winters in the SF Bay Area are rarely very cold but many people have wood burning stoves (anyway) and that smoke puts enough particulates in the atmosphere to sometimes trigger air warnings.
The Spare the Air website has a lot of useful tips and links to other websites covering air quality and transit issues. A few of those links are listed below. An earlier article, Environmental benefits (or not) of the Cash for Clunkers program, covered some factors to consider in choosing cleaner cars. The Green Book ratings are a list of cars carefully ranked by relative emissions.
Bay Area Air Quality Management District
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