Nighttime radical observations and chemistry

Abstract

The nitrate radical, NO(3), is photochemically unstable but is one of the most chemically important species in the nocturnal atmosphere. It is accompanied by the presence of dinitrogen pentoxide, N(2)O(5), with which it is in rapid thermal equilibrium at lower tropospheric temperatures. These two nitrogen oxides participate in numerous atmospheric chemical systems. NO(3) reactions with VOCs and organic sulphur species are important, or in some cases even dominant, oxidation pathways, impacting the budgets of these species and their degradation products. These oxidative reactions, together with the ozonolysis of alkenes, are also responsible for the nighttime production and cycling of OH and peroxy (HO(2) + RO(2)) radicals. In addition, reactions of NO(3) with biogenic hydrocarbons are particularly efficient and are responsible for the production of organic nitrates and secondary organic aerosol. Heterogeneous chemistry of N(2)O(5) is one of the major processes responsible for the atmospheric removal of nitrogen oxides as well as the cycling of halogen species though the production of nitryl chloride, ClNO(2). The chemistry of NO(3) and N(2)O(5) is also important to the regulation of both tropospheric and stratospheric ozone. Here we review the essential features of this atmospheric chemistry, along with field observations of NO(3), N(2)O(5), nighttime peroxy and OH radicals, and related compounds. This review builds on existing reviews of this chemistry, and encompasses field, laboratory and modelling work spanning more than three decades.

Isotopic composition of atmospheric nitrate in a tropical marine boundary layer

“…Moreover, the predominance of the nighttime P NO3+DMS (Fig. 2) during winter, even surpassing the daytime P NO2+OH as the main NO x sink, was found to be in agreement with previous studies (30,33). P NO3+DMS gave rise to the Δ 17 O winter peak in the SSM.…”

“…Recently, questions have emerged regarding the role of N 2 O 5 in models, especially in the clean marine atmosphere (5,6,29). These studies generally point to an overestimation of the uptake coefficient of N 2 O 5 (30). However, in the present case, sensitivity tests showed that the SSM was unaffected by three orders of magnitude changes in the N 2 O 5 uptake coefficient (range: 10 −3 to 1).…”

“…P NO3+DMS gave rise to the Δ 17 O winter peak in the SSM. This situation differs from more polluted environments, where N 2 O 5 played a pivotal role (30).…”

Direct measurement of NO<sub>3</sub> reactivity in a boreal forest

“…Both column-and point measurements of tropospheric NO 3 indicate a strong vertical gradient in its mixing ratio with significantly elevated levels aloft (Aliwell and Jones, 1998;Allan et al, 2002;von Friedeburg et al, 2002;Stutz et al, 2004;Brown et al, 2007a;Brown et al, 2007b;Brown and Stutz, 2012). The NO 3 gradient is the result of lower production rates close to the ground, where O 3 levels are depleted due to deposition and also lower loss rates aloft as the concentration of 5 reactive traces gases from ground level emissions decreases with altitude.…”

“…OH radicalinduced oxidation taking place mainly during daytime with the NO 3 radical (formed by reaction of O 3 with NO 2 , (R1)) accounting for the major fraction of radical-induced loss of BVOC at nighttime (Wayne et al, 1991;Atkinson, 2000;10 Atkinson and Arey, 2003a, b;Brown and Stutz, 2012;Mogensen et al, 2015;Ng et al, 2016;Liebmann et al, 2017). The rapid photolysis of NO 3 by sunlight (R5, R6) and reaction with NO (R2) typically reduces its lifetime to a few seconds during day-time.…”