Long-term daily mean mixing ratios of O-3, PAN, HNO3, and particle nitrate at a rural location in eastern Canada: Relationships and implied ozone production efficiency

Temporal trends (long term, annual, and daily) for concurrent observations of O-3, PAN, HNO3, and pNO(3)(-) (particle nitrate) are derived. Correlations between these compounds and the meteorological parameters temperature and precipitation are outlined using a partial correlation analysis and a principal component analysis. Long-term trends are observed for the nitrogen oxides that do not appear to be due to eastern North American sources. No long-term trend in O-3 is found, and a decrease in the efficiency of its production as function of nitrogen oxide abundance is indicated which may be caused by a decrease in the levels of hydrocarbons. Annual cycles of O-3 and PAN show similarity with a spring peak and a summer minimum. These compounds are positively correlated at all times but especially so in the spring, independent of the annual cycle, and it is inferred that a common mechanism drives the spring maximum. HNO3 and pNO(3)(-) do not show a similar spring maximum: HNO3 maximizes in the summer and pNO(3)(-) in the winter. On a day-to-day basis, PAN and O-3 show almost identical autocorrelation which is greater than that for HNO3 and pNO(3)(-), probably due to the variance introduced by precipitation scavenging of the latter. HNO3 and temperature correlate negative in the winter and positive in the summer with O-3 reflecting the different production mechanisms of HNO3. Positive correlation between HNO3 and PAN is seen suggesting that part of their variance is due to their common precursor NOx, while the negative correlation between PAN and temperature is probably reflecting the thermal instability of PAN. The results are used to infer the seasonal variation in the O-3 production efficiency as a function of nitrogen oxide abundance. A slight negative value is derived for the winter, and only during the period May to August is O-3 expected to be produced efficiently.