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Impact of VOCs and NOx on Ozone Formation in Moscow

Authors :: Elena Berezina
Nikolai Elansky
N. V. Pankratova
Konstantin V. Moiseenko
Andrei Skorokhod
Valery Belousov
I. B. Belikov
Source :: Atmosphere, Volume 11, Issue 11, Atmosphere, Vol 11, Iss 1262, p 1262 (2020)
Publication Year :: 2020
Publisher :: Multidisciplinary Digital Publishing Institute, 2020.
Abstract: Volatile organic compounds (VOCs), ozone (O3), nitrogen oxides (NOx), carbon monoxide (CO), meteorological parameters, and total non-methane hydrocarbons (NMHC) were analyzed from simultaneous measurements at the MSU-IAP (Moscow State University&mdash Institute of Atmospheric Physics) observational site in Moscow from 2011&ndash 2013. Seasonal and diurnal variability of the compounds was studied. The highest O3 concentration in Moscow was observed in the summer daytime periods in anticyclonic meteorological conditions under poor ventilation of the atmospheric boundary layer and high temperatures (up to 105 ppbv or 210 &mu g/m3). In contrast, NOx, CO, and benzene decreased from 8 a.m. to 5&ndash 6 p.m. local time (LT). The high positive correlation of daytime O3 with secondary VOCs affirmed an important role of photochemical O3 production in Moscow during the summers of 2011&ndash 2013. The summertime average concentrations of the biogenic VOCs isoprene and monoterpenes were observed to be 0.73 ppbv and 0.53 ppbv, respectively. The principal source of anthropogenic VOCs in Moscow was established to be local vehicle emissions. Yet, only about 5% of the observed isoprene was safely attributed to anthropogenic sources, suggesting significant contribution of biogenic sources into the total levels of ozone precursors. The non-linear O3&ndash NOx dependence shows a decrease in ground-level O3 with an increase in NOx during the summers of 2011&ndash 2013, which is typical for the VOC-sensitive photochemical regime of O3 formation. Nevertheless, during the elevated ozone episodes in July 2011, the photochemical regime of ozone production was either transitional or NOx-sensitive. Contribution of various anthropogenic and biogenic VOCs into the measured ozone values was evaluated. The ozone-forming potential (OFP) of total VOCs was 31&ndash 67 &mu g/m3 on average and exceeded 100 &mu g/m3 in the top 10% of high ozone events, reaching 136 &mu g/m3. Acetaldehyde, 1.3-butadiene, and isoprene have the highest ozone production potential in Moscow compared to that of other measured VOCs.