Characterizing the influence of highways on springtime NO_2 and NH_3 concentrations in regional forest monitoring plots

摘要

Highways are major sources of nitrogen dioxide (NO_2) and ammonia (NH_3). In this study, springtime NO_2 and NH3 concentrations were measured at 17 Ontario Forest Biomonitoring Network (OFBN) plots using passive samplers. Average springtime NO_2 concentrations were between 1.3 μg m~(-3) and 27 μg m~(-3), and NH_3 concentrations were between 0.2 μg m~(-3) and 1.7 μg m~(-3), although concentrations measured in May (before leaf out) were typically twice as high as values recorded in June. Average NO_2 concentrations, and to a lesser extent NH_3, could be predicted by road density at all radii (around the plot) tested (500 m, 1000 m, 1500 m). Springtime NO_2 concentrations were predicted for a further 50 OFBN sites. Normalized plant/lichen N concentrations were positively correlated with estimated springtime NO_2 and NH_3 concentrations. Epiphytic foliose lichen richness decreased with increasing NO_2 and NH_3, but vascular plant richness was positively related to estimated springtime NO_2 and NH_3.