Air Quality & Air Pollution

I. Overview

Air quality is one of the most widely recognized environmental effects of transportation. The Clean Air Act and its amendments have played an important role in reducing motor vehicle emissions of major criteria pollutants. Yet other pollutants are not being monitored, and this has serious implications for the global context of air pollution in comparison with the local context.

Transportation contributes to air pollution primarily through the release of pollutants during the fuel combustion process. Pollutants are also emitted during the refining and processing of fuels and fuel evaporation. Transportation sources consumed about 66 percent of the petroleum used in the U.S. in 1997.

An examination of transportation and environmental issues depends on its specific local context. European Union countries have implemented a significantly different set of emissions standards and regulations. Taxes on fuel differ widely from one country to the next, which has a direct impact on fuel usage and consequently on environmental impact.

The costs of air pollution are difficult to estimate, primarily because of the uncertainties associated with health effects: the range falls between 0.2 and 0.4% of GDP (excluding the costs associated with greenhouse gases). Several studies report health and even mortality impacts, largely from hydrocarbon emissions, associated with cancer, respiratory diseases (e.g. asthma), and heart disease.

II. Local Context

With the introduction of the Clean Air Act, the EPA has set national air quality standards for six principal pollutants (referred to as "criteria" pollutants): carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM), and sulfur dioxide (SO2). The pollutant ozone is not emitted directly into the air, but is formed when sunlight acts on emissions of nitrogen oxides (NOx) and volatile organic compounds (VOC).
Monitoring data from across the U.S. show decreases in air pollutant concentrations
since the early 1970s. Between 1978 and 1997, concentrations of ozone (one-hour) have fallen by 30 percent, carbon monoxide concentrations have fallen by 60 percent, and lead concentration have fallen by 97 percent. Between 1988 and 1997, the total number of days exceeding air quality standards has dropped 56 percent in Southern California and 66 percent in the rest of the United States.

Comparison of 1970 and 1997 Emissions

Source: National Air Pollutant Emission Trends Update, 1970-1997

NOx, VOCs and PM all result in ecological damage. Ozone damages forests (both trees and plants), especially in mountainous regions (e.g. the impact on Appalachia of long-distance NOx moves from the cities of the Midwest and the South East), and results in reduced biodiversity.

Nitrogen enrichment affects soil and plants, especially by stimulating plant growth with implications for species balance and incurring biological damages in coastal zones (e.g. Chesapeake Bay, Long Island Sound).

NOx combines with SOx to produce acid rain, with damages to forests, other plants and aquatic life (e.g. fish); of course, most of the SOx comes from power plants and other stationary sources. CO is odorless, colorless but is very toxic. Most of it comes from transport, resulting from incomplete combustion. Lead is dangerous (child retardation, hypertension, heart attacks), but is disappearing as a transport-related pollutant as lead-free gasoline spreads.

Despite the current trends, the failure of the Clean Air Act to measure other pollutants has greatly restricted the progress toward clean air improvements in the U.S. Powerful lobbies of the automobile industry have been largely successful in delaying implementation of lower-polluting technology.

III. Global Implications

Although CO2 is not one of the air pollutants specified in the Clean Air Acts, it is a target pollutant in the air pollution legislation of many other countries due its contribution to the greenhouse effect. Greenhouse gases have increased significantly since pre-industrial times (30% for CO2, more than 100% for CH4, and 15% for N2O). It is estimated further that CO2 concentrations could double their pre-industrial levels by 2100.

Carbon Dioxide (CO2) and the following greenhouse gases are major contributors to global warming: methane [CH4], nitrous oxide [N2O], ozone [O3], water vapor, industrially produced chlorofluorocarbons [CFCs], hydrochlorofluorocarbons [HCFCs], and hydrofluorocarbons [HFCs])

The impact of transportation on the global scale then is highly controversial on the global scale. It is the object of intense scrutiny by some countries, while other countries are concerned for their economic development and would prefer to dismiss the issue until more conclusive scientific evidence exists. Nevertheless, the estimated increase in global temperature varies between 1 to 3.5 degrees celcius over the next century as a result of that warming. Transportation will play a significant role in that increase.

IV. More Information

A. Federal Agency

1. Environmental Protection Agency

a. Transportation Air Quality (TRAQ) Center
EPA's Transportation Air Quality (TRAQ) Center provides state and local air quality regulators and transportation planners with access to critical information regarding transportation programs and mobile source incentive-based programs, partnership opportunities, grant funding sources, useful contact names, and technical assistance.

b. Alliance for Clean Air and Transportation (ACAT)

In collaboration with the U.S. DOT and U.S. EPA, ACAT is an interactive forum established to provide support for core transportation/air quality messages and help sustain the It All Adds Up to Cleaner Air initiative.

c. Smart Travel Resource Center
The U.S. Environmental Protection Agency's Smart Travel Resource Center is a clearinghouse of information on transportation / air quality related public education and information campaigns and programs.

US Environmental Protection Agency
Smart Travel Resource Center

2. U.S. Department of Transportation

a. Department of Transportation (main page)

b. Federal Highway Administration

c. Office of Highway Policy Information (OHPI)
The Office of Highway Policy Information (OHPI) provides a repository of highway information and statistics. The Office collects, analyzes and distributes highway related data from federal, state and local sources.

3. Other
www.bts.gov
www.epa.gov/oar/oahome.html

www.epa.gov/oar/oaqps

www.epa.gov/oms/traq

www.epa.gov/globalwarming

B. Non-Agency
www.4cleanair.org
www.nas.edu/trb

Prepared by Nathaniel Trumbull and Professor Christine Bae. Last updated 02/09/2000.