Analysis of passive-sampler monitored atmospheric ammonia at 74 sites across southern Ontario, Canada

[摘要] Weekly/biweekly concentrations of atmospheric NH₃were collected using passive samplers at 74 sites across southern Ontario,Canada, during the period from June 2006 to March 2007 with eighteen sitesrunning as early as March 2006. The annual average of NH₃ (AAN) at allthe sites across southwestern Ontario was over 1 μg m⁻³, a valuethat was recently proposed as the new critical level for protectingvegetation. High AAN values (3.6–6.1 μg m⁻³) were observed ateight sites located inside the intensive livestock production zones. AANvalues at the sites across southeastern Ontario were generally lower than 1 μg m⁻³and the values were less than 0.4 μg m⁻³ atnon-agricultural sites. Agricultural sites generally showed the highestconcentrations in spring to summer and the lowest in winter, but theoccurrence time of the peak concentration varied among the sites, whichcould be due to their different land use and thus different fertilizerapplication intensities or periods. Seasonal trends of NH₃concentration at some non-agricultural sites were somewhat similar to thoseat the agricultural sites, but the peak concentration appeared a few weekslater than at the agricultural sites. Surprisingly, at several remotenon-agricultural sites, NH₃ concentrations were not decreasing inwinter and were sometimes increasing to a level higher than those in summer,which could be caused by different transport mechanisms in differentseasons. A sharp increase in NH₃ concentration was also surprisinglyobserved at 20 out of the 74 sites during the coldest two weeks when ambienttemperature was lower than −7 °C, and cannot be explained byknown sources or with existing knowledge. The NH₃ emission inventory for the region of southern Ontario was evaluated usingthe measurement data and emissions within two small zones in this region were identifiedto be potentially underestimated.

[学科分类] 地球化学与岩石