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Introduction to the December 2019 issue of EM Magazine on Wintertime Air Quality
Citation:
Kelly, J. AND G. Sarwar. Introduction to the December 2019 issue of EM Magazine on Wintertime Air Quality. EM: AIR AND WASTE MANAGEMENT ASSOCIATION'S MAGAZINE FOR ENVIRONMENTAL MANAGERS. Air & Waste Management Association, Pittsburgh, PA, Dec:1, (2019).
Impact/Purpose:
Severe air pollution episodes occur in the U.S. and other parts of the world in wintertime when meteorological inversions trap particles and other pollutant emissions near their sources. In addition, wintertime inversions can lead to elevated particulate matter and ozone concentrations under certain conditions. The sources, meteorology, and formation pathways for wintertime pollution differ from those that lead to high summertime pollution. This EM issue provides several examples of contemporary wintertime air quality challenges in different parts of the world.
Description:
Air pollution is a major risk factor for premature mortality worldwide. In 2017, fine particulate pollution is estimated to have contributed to 2.9 million premature deaths globally and ozone pollution to nearly a half million death. Air pollution levels vary dramatically throughout the world and by season, and many areas of the world experience especially severe air pollution during winter. For example, the highest concentrations of fine particulate matter (PM2.5) occur in winter in Delhi, India; Beijing, China; Dhaka, Bangladesh; and San Joaquin Valley, U.S. The timing of the peak in national average PM2.5 concentrations in the U.S. recently switched from summertime to wintertime. Severe wintertime air pollution is driven in part by meteorology. Cold ground temperatures cause the layer of air close to the surface to be cooler than the air above. Layering of cool air under warm air promotes atmospheric stability, which suppresses vertical mixing and dilution of surface emissions. Stagnant air conditions can be intensified by high pressure systems that further suppress atmospheric mixing and trap air pollutants near the surface. Wintertime pollution can be especially bad in valleys where horizontal air transport and ventilation is blocked by terrain. Wintertime air pollution is also driven by pollutant emissions specific to the season. Cold temperatures lead to enhanced emissions associated with home heating. Use of raw coal for home heating has been identified as a major pollution source in Ulaanbaatar, Mongolia, and residential wood combustion is an important pollution source in mountain valleys in the U.S. In Northern India, residential biomass burning is the major contributor to PM2.5 concentrations in December-February and burning of crop stubble from farms in Punjab and Haryana is a major pollution source in October-November. Open burning of municipal solid waste has also been recognized as an important wintertime emission source in Indian cities. In this issue of EM magazine, several examples of wintertime air pollution are described.