On June mean hourly O
3.1.4. Nitrogen oxides
At PAVA, the mean NO and NOx mixing ratios were 0.4 ± 0.6 and 2.1 ± 1.8 ppbv over the duration of measurement. These values are indicative of background concentrations (Table 1) and the overall NO2/NOx ratio of 0.82 indicates a high degree of oxidation and limited nearby primary NO emissions. However, the peak hourly NO and NOx recorded were 9.9 and 22.0 ppbv (1800 PST, October 27, 2012), with an NO2/NOx ratio of 0.55 indicating a substantial percentage of un-oxidized NO, suggesting that local emission sources sometimes contribute to exceptionally high NOx mixing ratios.
3.1.5. Fine particulate Dehydroepiandrosterone & mercury
The overall mean daily PM2.5 concentration at PAVA was 7.4 μg m− 3 with a anabolic reactions maximum daily concentration of 54 μg m− 3 observed in August 2013. Mean daily PM2.5 at PAVA was not correlated with mean daily O3 (r2 = 0.01) or with any other gas parameter except for a weak significant correlation with mean daily CO (r2 = 0.21, p < 0.01). However, mean daily PM2.5 concentrations above the 90th percentile (10.7 μg m− 3) were moderately correlated with CO (r2 = 0.36, p < 0.01) and with mean daily O3 (r2 = 0.16, p < 0.01). This reflects the influence of wildfire smoke on CO and PM2.5 concentrations at PAVA, and the tendency for the highest O3 to occur during such conditions (discussed below).