Low levels of nitryl chloride at ground level: nocturnal nitrogen oxides in the Lower Fraser Valley of British Columbia

Abstract

Abstract. The nocturnal nitrogen oxides, which include the nitrate radical (NO3), dinitrogen pentoxide (N2O5), and its uptake product on chloride containing aerosol, nitryl chloride (ClNO2), can have profound impacts on the lifetime of NOx (= NO + NO2), radical budgets, and next-day photochemical ozone (O3) production, yet their abundances and chemistry are only sparsely constrained by ambient air measurements. Here, we present a measurement data set collected at a routine monitoring site near the Abbotsford International Airport (YXX) located approximately 30 km from the Pacific Ocean in the Lower Fraser Valley (LFV) on the west coast of British Columbia. Measurements were made from 20 July to 4 August 2012 and included mixing ratios of ClNO2, N2O5, NO, NO2, total odd nitrogen (NOy), O3, photolysis frequencies, and size distribution and composition of non-refractory submicron aerosol (PM1). At night, O3 was rapidly and often completely removed by dry deposition and by titration with NO of anthropogenic origin and unsaturated biogenic hydrocarbons in a shallow nocturnal inversion surface layer. The low nocturnal O3 mixing ratios and presence of strong chemical sinks for NO3 limited the extent of nocturnal nitrogen oxide chemistry at ground level. Consequently, mixing ratios of N2O5 and ClNO2 were low (< 30 and < 100 parts-per-trillion by volume (pptv) and median nocturnal peak values of 7.8 and 7.9 pptv, respectively). Mixing ratios of ClNO2 frequently peaked 1–2 h after sunrise rationalized by more efficient formation of ClNO2 in the nocturnal residual layer aloft than at the surface and the breakup of the nocturnal boundary layer structure in the morning. When quantifiable, production of ClNO2 from N2O5 was efficient and likely occurred predominantly on unquantified supermicron-sized or refractory sea-salt-derived aerosol. After sunrise, production of Cl radicals from photolysis of ClNO2 was negligible compared to production of OH from the reaction of O(1D) + H2O except for a short period after sunrise.

Shipborne measurements of ClNO<sub>2</sub> in the Mediterranean Sea and around the Arabian Peninsula during summer

“…industrial combustion, cooling towers, natural gas extraction, and suspension of road salt) and sea salt chloride transported inland. Further studies reported significant mixing ratios of ClNO 2 at a semi-rural site in continental Germany (Phillips et al, 2012(Phillips et al, , 2016 and at a mid-continental urban site in Canada (Mielke et al, 2011(Mielke et al, , 2016. Observations at continental sites could be reproduced by a global model (Wang et al, 2019) when considering the transport of HCl (aq), which had been initially formed in the gas phase through acid displacement in coastal regions.…”

“…The formation of ClNO 2 can have a significant impact on regional NO x cycling and radical chemistry, especially in the polluted coastal and marine boundary layer (Simon et al, 2009;Riedel et al, 2014;Sarwar et al, 2014). The Cl atoms formed in Reaction (R2) can enhance oxidation rates of several volatile organic compounds (VOCs), especially during early morning hours (Phillips et al, 2012;Riedel et al, 2012a;Young et al, 2012) thus contributing to photochemical ozone production (Simon et al, 2009;Riedel et al, 2014;Sarwar et al, 2014;Faxon et al, 2015;Wang et al, 2019).…”

“…the Los Angeles Basin in California (Riedel et al, 2012a;Wagner et al, 2012;Young et al, 2012). Other studies included coastal sites in Canada (Osthoff et al, 2018) and coastal/urban sites in the United Kingdom (Bannan et al, 2015(Bannan et al, , 2017Priestley et al, 2018;Sommariva et al, 2018). Whereas ClNO 2 was initially believed to play a significant role only in areas with marine influence (Behnke et al, 1997;Keene et al, 1999), midcontinental measurements in the US (Thornton et al, 2010;Riedel et al, 2013;Faxon et al, 2015) revealed the im-portance of anthropogenic sources (e.g.…”

Stable sulfur isotope measurements to trace the fate of SO2 in the Athabasca oil sands region

“…WBEA SO 2 data were used with a sampling interval of 5 min. Ozone and NO 2 mixing ratios were measured by UV absorption using a Thermo 49i O 3 monitor every 10 s and a blue diode laser cavity ring-down spectrometer every 1 s, respectively (data were averaged to 1 min; Odame-Ankrah, 2015; Paul and Osthoff, 2010). The slope uncertainties in these measurements were ±1 and ±10 %, respectively.…”

“…The slope uncertainties in these measurements were ±1 and ±10 %, respectively. Radiometer measurements using a pair of spectral radiometers (one facing the zenith, the other the nadir direction) were used to determine actinic flux and to calculate photolysis frequencies (j values; Osthoff et al, 2018). Iron (Fe) and Manganese (Mn) were measured by semi-continuous X-ray fluorescence measurements of metals taken every hour on a filter tape with a measurement uncertainty of ±10 % (Phillips-Smith et al, 2017).…”