Summertime NOx NOy and Ozone at a Site in Rural Ontario: Results from SONTOS

Measurements of NOy, NOx NO, SO2, PAN, HNO3, O3, and CO, obtained as part of SONTOS, have been examined to give a picture of the typical chemistry at this location, and for comparison with other North American sites. The total amount of odd nitrogen (NOy) at the Hastings site is less than found at other North American sites, due to the distance of the site from sources and the absence of major anthropogenic sources north west of the site. The air masses also appear younger, containing a higher fraction of NOx, although the chain length for ozone production is similar. The ozone concentrations at the site are lower than reported elsewhere, and the late afternoon maximum shows that it is typically produced elsewhere and transported to the site. A similar conclusion can be drawn from the PAN measurements. There appears to be a significant local NOx source. The flux needed to explain the observations is within the range of values from soil emissions, but a strong correlation with CO, and no correlation with SO2, suggest a mobile combustion source.