TAILIEUCHUNG - Air pollution removal by urban trees and shrubs in the United States

Decreases in pH and ANC are often paral- leled by changes in element concentrations including increases in Al +3 concentrations and decreases in Ca +2 . High dissolved Al +3 concen- trations can have toxic effects on many types of aquatic biota, and at extreme levels few aquatic species can survive (Table 1). Organic forms of Al +3 are much less toxic than inorganic forms. Emerging research suggests that Ca +2 concentra- tions in streamwater are also an important bio- logical indicator. Acidifying deposition has accelerated the leaching of Ca +2 from soils to surface waters gradually decreasing the avail- able pool of Ca +2 in soils and lowering Ca +2 concentrations in runoff. This soil depletion together with decreases in leaching associated with declines in acidifying deposition is con- tributing to. | ELSEVIER Available online at Urban Forestry Urban Greening 4 2006 115-123 URBAN FORESTRY ljr 1n GREENING ufug Air pollution removal by urban trees and shrubs in the United States David J. Nowak Daniel E. Crane Jack c. Stevens USDA Forest Service Northeastern Research Station 5 Moon Library SUNY-ESF Syracuse NY 13210 USA Abstract A modeling study using hourly meteorological and pollution concentration data from across the coterminous United States demonstrates that urban trees remove large amounts of air pollution that consequently improve urban air quality. Pollution removal O3 PM 10 NO2 so2 CO varied among cities with total annual air pollution removal by US urban trees estimated at 711 000 metric tons billion value . Pollution removal is only one of various ways that urban trees affect air quality. Integrated studies of tree effects on air pollution reveal that management of urban tree canopy cover could be a viable strategy to improve air quality and help meet clean air standards. Published by Elsevier GmbH. Keywords Air quality Urban forests Urban forestry Environmental quality 1. Introduction Air pollution is a major environmental concern in most major cities across the world. An important focus of research has been on the role of urban vegetation in the formation and degradation of air pollutants in cities. Through the emission of volatile organic compounds VOC urban trees can contribute to the formation of ozone O3 Chameides et al. 1988 . However more integrative studies are revealing that urban trees particularly low voc emitting species can be a viable strategy to help reduce urban ozone levels Cardelino and Chameides 1990 Taha 1996 Nowak et al. 2000 particularly through tree functions that reduce air temperatures transpiration remove air pollutants dry deposition to plant surfaces and reduce building energy and consequent power plant emissions . temperature reductions tree shade . One study Nowak et al. 2000 .

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