An Assessment of the Effectiveness of California’s Local Air Pollution Controls on Agricultural Sources

Abstract

Air pollution has been recognized as a significant environmental problem in California since the early 20th century. Between 1905 and 1912, regulations were enacted by the city council of Los Angeles to regulate emissions [1]. As motor vehicle traffic increased, a new type of smog was observed and described: the “Los Angeles” or photochemical smog, as distinct from the “London” smog that resulted from coal combustion. Arie Haagen-Smit from Caltech characterized the chemistry of this smog and identified ozone as the principal oxidant in the early 1950’s. Meanwhile, the first air district in the U.S. was created in Los Angeles in 1947, and was later merged with other local districts in 1977 to form the South Coast Air Quality Management District [1]. Negative effects of air pollution have been extensively documented, and include impairment of human lung function, degradation of materials, and injury to plants. In addition to affecting human health, the high ambient ozone levels found in Southern California and the San Joaquin Valley also cause yield reductions up to 30% for some crops [2]. In addition to having some of the nation’s most polluted air basins, California also has the nation’s most stringent set of state and local air quality standards. Although regulation has led to improvements in air quality [3], exceedances of air quality standards still take place. For example, between 1990 and 1998, the San Joaquin Valley Air Basin experienced an average of 97 days per year above the eight-hour ozone standard, while the Sacramento Valley Air Basin experienced an average of 30 days per year above the standard during the same time period [4]. Farming and livestock operations are significant sources of emissions in California, and bear the negative effects of specific air pollutants as well. Agriculture-related air pollution results from primary emissions from machinery and vehicles employed in production, chemical compounds used in the course of production, e.g. pesticides, as well as emissions from the agricultural systems themselves. For example, agricultural livestock emit nitrogen compounds such as oxides of nitrogen (NOx) and ammonia. Vehicles used in agricultural production emit volatile organic compounds (VOCs), NOx and carbon monoxide (CO) [5]. These emissions may lead to the formation of secondary air pollutants, such as ozone, that are deleterious to workers as well as crops [6].