Study of the unknown HONO daytime source at a European suburban site during the MEGAPOLI summer and winter field campaigns

Abstract

International audienceNitrous acid measurements were carried out during the MEGAPOLI summer and winter field campaigns at SIRTA observatory in Paris surroundings. Highly variable HONO levels were observed during the campaigns, ranging from 10 ppt to 500 ppt in summer and from 10 ppt to 1.7 ppb in winter. Significant HONO mixing ratios have also been measured during daytime hours, comprised between some tenth of ppt and 200 ppt for the summer campaign and between few ppt and 1 ppb for the winter campaign. Ancillary measurements, such as NO_x , O₃ , photolysis frequencies, meteorological parameters (pressure, temperature, relative humidity , wind speed and wind direction), black carbon concentration , total aerosol surface area, boundary layer height and soil moisture, were conducted during both campaigns. In addition, for the summer period, OH radical measurements were made with a CIMS (Chemical Ionisation Mass Spectrometer). This large dataset has been used to investigate the HONO budget in a suburban environment. To do so, calculations of HONO concentrations using PhotoStationary State (PSS) approach have been performed, for daytime hours. The comparison of these calculations with measured HONO concentrations revealed an underestimation of the calculations making evident a missing source term for both campaigns. This unknown HONO source exhibits a bell-shaped like average diurnal profile with a maximum around noon of approximately 0.7 ppb h⁻¹ and 0.25 ppb h⁻¹ , during summer and winter respectively. This source is the main HONO source during daytime hours for both campaigns. In both cases, this source shows a slight positive correlation with J (NO₂) and the product between J (NO₂) and soil moisture. This original approach had, thus, indicated that this missing source is photolytic and might be heterogeneous occurring at ground surface and involving water content available on the ground. Published by Copernicus Publications on behalf of the European Geosciences Union. 2806 V. Michoud et al.: Study of the unknown HONO daytime sourc

Impacts of an unknown daytime HONO source on the mixing ratio and budget of HONO, and hydroxyl, hydroperoxyl, and organic peroxy radicals, in the coastal regions of China

“…After sunrise, HONO mixing ratios are usually in low concentrations due to the strong photolysis of HONO. However, many field experiments have found daytime HONO mixing ratios that are unexpectedly higher than the theoretical steady value (∼ 10 ppt), in both urban and rural areas: e.g., 0.15-1.50 ppb in Asia (Su et al, 2008;Spataro et al, 2013), 0.01-0.43 ppb in Europe Acker and Möller, 2007;Sörgel et al, 2011;Michoud et al, 2014), 0.02-0.81 ppb in North America (Zhou et al, 2002a, b;Ren et al, 2010;Villena et al, 2011;Wong et al, 2012;VandenBoer et al, 2013), 2.00 ppb (maximum) in South America (Elshorbany et al, 2009), and 0.015-0.02 ppb in Antarctica (Kerbrat et al, 2012) (Fig. 1).…”

Measurements of PM10 ions and trace gases with the online system MARGA at the research station Melpitz in Germany – A five-year study

“…Beside possible positive artifacts caused by wet chemical sampling, HONO daytime sources also exist and explain low HONO concentrations despite of a strong photolysis. Several HONO daytime sources were discussed in literature (Li et al 2014;Michoud et al 2014;Spataro and Ianniello 2014;VandenBoer et al 2014).…”

Comparison of OH reactivity measurements in the atmospheric simulation chamber SAPHIR

“…-application of the correction of measurements is recommended due to the deviation from pseudo first-order conditions in CRM instruments by empirical correction factors (Michoud et al, 2014);…”