Ground and Airborne U.K. Measurements of Nitryl Chloride: An Investigation of the Role of Cl Atom Oxidation at Weybourne Atmospheric Observatory

Abstract

Nitryl chloride (ClNO2) measurements from the Weybourne Atmospheric Observatory (WAO) are reported from March to April 2013 using a quadruple chemical ionization mass spectrometer with the I− ionization scheme. WAO is a rural coastal site with generally low NOx concentrations, a type of location poorly studied for ClNO2 production. Concentrations of ClNO2 exceeded that of the limit of detection (0.8 ppt) on each night of the campaign, as did concentrations of N2O5, which was also measured simultaneously with the Cambridge Broadband Cavity Enhanced Absorption Spectrometer. A peak concentration of 65 ppt of ClNO2 is reported here. Vertical profiles of ClNO2 from early‐ to middle‐morning flights in close proximity to WAO are also reported, showing elevated concentrations at low altitude. The photolysis of observed ClNO2 and a box model utilizing the Master Chemical Mechanism modified to include chlorine chemistry was used to calculate Cl atom concentrations. This model utilized numerous VOCs from the second Tropospheric Organic Chemistry project in 2004, at the same location and time of year. From this the relative importance of the oxidation of three groups of measured VOCs (alkanes, alkenes, and alkynes) by OH radicals, Cl atoms, and O3 is compared. Cl atom oxidation was deemed generally insignificant at this time and location for total oxidation due to the much lower concentration of ClNO2 observed, even following the night of greatest ClNO2 production.

Seasonal and geographical variability of nitryl chloride and its precursors in Northern Europe

“…The measurements presented here, and those by Bannan et al . (; ), suggest that ClNO 2 levels in the United Kingdom are controlled by the gas‐phase precursors (O 3 and NO 2 ), rather than by the uptake and reaction of N 2 O 5 with particulate chloride. To investigate the relationship between ClNO 2 , O 3 and NO 2 in more detail, a simple box model was developed.…”

“…More recently, Bannan et al . () reported peak concentrations of up to 65 ppt in Weybourne (United Kingdom).…”

“…This result is consistent with the spring observations previously made by Bannan et al . () in Weybourne: although O 3 concentrations were higher (45–50 ppb) than in Leicester, the mean ClNO 2 concentration was about a factor of 6 lower (∼15 ppt) due to lower NO x levels in Weybourne.…”

“…() and Bannan et al . (; ), shows that the presence of ClNO 2 is widespread across Northern Europe: where there is sufficient particulate chloride and the total aerosol surface area is large enough (e.g., where sea salt aerosol is abundant), ClNO 2 chemistry is expected to occur. These conditions are typical of the United Kingdom and large areas of Northern Europe; they are also likely to be encountered in other parts of the world and are particularly relevant for coastal urbanized regions and megacities.…”

Production of N<sub>2</sub>O<sub>5</sub> and ClNO<sub>2</sub> in summer in urban Beijing, China

“…To ascertain the N 2 O 5 concentration in the line, the flow is diverted through a heated line to decompose the N 2 O 5 and into to a Thermo Scientific 42i NO x analyzer in which it is detected as NO 2 . According to the intercomparisons with the BBCEAS, including this study and others (e.g., Le Breton et al, 2014;Bannan et al, 2017), the possible interference of NO y on the NO x analyzer is not deemed important in terms of our reported N 2 O 5 concentrations.…”