Daytime nitrogen oxides and photochemistry in the Lower Fraser Valley of British Columbia

It is well recognized that the Lower Fraser Valley (LFV) of British Columbia is prone to episodes of poor air quality and exceedences of ozone (O3) and fine particulate matter standards. Ainslie and Steyn (2007) have investigated 20 years of O3 air quality data in the LFV region and deduced the existence of a "mystery [O3] precursor" which builds up prior to exceedence days. One potential candidate for such a precursor is nitryl chloride (ClNO2), which forms from reactive uptake of dinitrogen pentoxide (N2O5) on chloride containing aerosol. Here, we present measurements of nitrogen oxides (NO, NO2, PAN, NO3, N2O5, ClNO2, and NOy), O3, and photolysis frequencies at a site near the Abbotsford International Airport from July 20 to August 4, 2012. Instantaneous O3 production rates were calculated from the perturbation of the photostationary state that exists between NO2, NO and O3. Daytime maxima ranged from 4 parts-per-trillion by volume (pptv) / s to > 40 pptv/s and were well above net O3 production rates, which peaked at 5 pptv/s, suggesting the presence of strong O3 sinks during daytime. Primary radical production of Cl atoms (from photolysis of ClNO2) was negligible compared to that of OH (from O1D + H2O) except for a short period after sunrise (05:30 - 07:00 local time). However, because conditions leading to O3 exceedences did not develop during the study period, it remains unclear if ClNO2 formation plays a significant role on exceedence days in the LFV.