Polycyclic aromatic hydrocarbons in Costa Rican air and soil: A tropical/temperate comparison |
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| Institution: | 1. Department of Chemistry and Department of Physical and Environmental Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, Ont., Canada M1C 1A4;2. Instituto Regional de Estudios en Sustancias Toxicas, Campus Omar Dengo, Universidad Nacional, Heredia, Costa Rica;3. Aquatic Ecosystem Protection Research Division, Environment Canada, 867 Lakeshore Road, Burlington, Ont., Canada L7R 4A6;1. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. SRM Research Institute, SRM University, India;3. Environmental Engineering, School of Resource and Environmental Science, Wuhan University, Wuhan 430079, China;1. College of Urban and Environmental Sciences, Peking University, Beijing 100871, China;2. Provincial Key Laboratory of Environmental Engineering, Jiangsu Provincial Academy of Environmental Sciences, Nanjing 210036, China;3. Stockbridge School of Agriculture, University of Massachusetts, Amherst, MA 01003, United States;1. State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China;2. School of Environment, Hangzhou Institute for Advanced Study, UCAS, Hangzhou, 310024, China;3. University of Chinese Academy of Sciences, Beijing, 100049, China;1. Air Quality Processes Research Section, Environment Canada, 4905 Dufferin Street, Toronto, ON M3H 5T4, Canada;2. Analysis and Air Quality Section, Environment Canada, Ottawa, ON K1A 0H3, Canada;1. Environmental Analysis Laboratory, School of Environmental Sciences, Universidad Nacional, Heredia, Costa Rica;2. Universidad Autónoma Metropolitana, Azcapotzalco, D.F., Mexico |
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| Abstract: | Surface soil and passive air samples from a network of 23 sampling sites across Costa Rica were analyzed for polycyclic aromatic hydrocarbons (PAHs), allowing for an evaluation of absolute levels, spatial distribution patterns, air/soil concentration (A/S) ratios and relative composition. Annual mean concentrations of four-ring PAHs in air were low (median of approximately 40 pg m?3), except in Costa Rica's densely populated central valley (approximately 650 pg m?3). PAH concentrations in soil were also low (median of 5 ng g?1 dry weight) and comparable to those reported for other tropical regions. These low soil concentrations result in A/S ratios of four-ring PAHs in Costa Rica that are higher than the equilibrium air–soil partitioning coefficients and also higher than A/S ratios reported for temperate locations. A series of model calculations of increasing complexity were used to seek an explanation for variable A/S ratios of PAHs under tropical and temperate conditions. Temperature-driven changes in air–soil partitioning and differences in PAH degradability under temperate and tropical conditions are insufficient to explain the higher soil concentrations and lower A/S ratios in temperate regions. However, these can be explained by atmospheric deposition of PAHs during historical periods of much higher emissions and air concentrations and by persistence of PAHs in soils on the order of decades. Low PAH concentrations in tropical soils were found to be consistent with constant or increasing emissions, and in particular, do not require that degradation rates in soil are much faster than in temperate areas. In comparison to temperate soils, soils from Costa Rica and other tropical regions have a higher relative abundance of the lighter PAHs. This likely reflects a higher source contribution from biomass burning in the tropics, as well as the preferential loss of lighter PAHs from temperate soils that experienced high PAH deposition in the past. |
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