Reid, Holly

The spatial and temporal variation in atmospheric nitrogen dioxide (NO2), ammonia (NH3), and 17 elements (V, Cr, Fe, Ni, Cu, Zn, As, Cd, Pb, Mg, Al, Ca, Co, Se, Sb, Mn, and Na) were measured at 40 road side locations along a ~250 km traffic density gradient of 40,000–400,000 vehicles on the King's Highway 401, in Ontario, Canada. Elemental concentrations were measured over a year, using moss bags as passive samplers, for four quarterly three-month exposure periods (October 2015 – October 2016). Gaseous NO2 and NH3 concentrations were measured using Willem's badge passive diffusive samplers for twelve one-week exposure periods (one per month: October 2015–October 2016). Dry deposition of nitrogen was estimated using the inferential method. There were significant linear relationships between NO2 and NH3 and average annual daily traffic (AADT) volumes across the study area; higher concentrations corresponded to higher volume traffic sites. Average NO2 concentrations at sites ranged from 23.5 to 73 μg/m3, with an annual average of 43.7 μg/m3. Ammonia ranged from 2.56 to 13.55 μg/m3, with an annual average of 6.44 μg/m3. There were significant quarterly variations in NO2, with concentrations peaking during the winter months. In contrast, NH3 showed no significant quarterly variation, but a slight peak occurred during the summer. Gaseous NO2 and NH3 were highly positively correlated (r = 0.63), suggesting a common emission source from traffic. Concentrations in exposed moss were determined by subtracting the total concentration of each metal in the exposed sample from the background concentration present in the moss. Relative accumulation factors (RAF) and contamination factors were also calculated to determine the anthropogenic influence on tissue concentrations in exposed moss. All metals showed elevated levels versus background concentrations, with all metals except Ni and Co showing considerable enrichment. The highest levels of contamination were from V, Cr, Fe, Zn, Cd, Sb, Pb and Na. Principal component analysis indicated 5 clear clusters of related elements, with PC1 accounting for 36.2% and PC2 accounting for 25.6% of the variance. Average annual daily traffic was significantly related to Cr, Fe, Cu, Sb, Mn, Al, and Na. Road side monitoring shows consistently higher concentrations than active monitoring sites located further from the edge of the road, indicating a need for increased road side monitoring in Ontario, Canada.