Measurements of the sum of HO<sub>2</sub>NO<sub>2</sub> and CH<sub>3</sub>O<sub>2</sub>NO<sub>2</sub> in the remote troposphere

Abstract

Abstract. The chemistry of peroxynitric acid (HO 2 NO 2 ) and methyl peroxynitrate (CH 3 O 2 NO 2 ) is predicted to be particularly important in the upper troposphere where temperatures are frequently low enough that these compounds do not rapidly decompose. At temperatures below 240 K, we calculate that about 20% of NO y in the mid-and high-latitude upper troposphere is HO 2 NO 2 . Under these conditions, the reaction of OH with HO 2 NO 2 is estimated to account for as much as one third of the permanent loss of hydrogen radicals. During the Tropospheric Ozone Production about the Spring Equinox (TOPSE) campaign, we used thermal dissociation laser-induced fluorescence (TD-LIF) to measure the sum of peroxynitrates ( PNs≡HO 2 NO 2 +CH 3 O 2 NO 2 +PAN+PPN+. . . ) aboard the NCAR C-130 research aircraft. We infer the sum of HO 2 NO 2 and CH 3 O 2 NO 2 as the difference between PN measurements and gas chromatographic measurements of the two major peroxy acyl nitrates, peroxy acetyl nitrate (PAN) and peroxy propionyl nitrate (PPN). Comparison with NO y and other nitrogen oxide measurements confirms the importance of HO 2 NO 2 and CH 3 O 2 NO 2 to the reactive nitrogen budget and shows that current thinking about the chemistry of these species is approximately correct. During the spring high latitude conditions sampled during the TOPSE experiment, the model predictions of the contribution of (HO 2 NO 2 +CH 3 O 2 NO 2 ) to NO y are highly temperature dependent: on average 30% of NO y at 230 K, 15% of NO y at 240 K, and <5% of NO y above 250 K. The temperature dependence of the inferred concentrations corroborates the contribution of overtone photolysis to the photochemistry of peroxynitric acid. A model that includes IR photolysis (J=1×10 −5 s −1 ) agreed with the observed sum

Global and regional effects of the photochemistry of CH&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt;NO&lt;sub&gt;2&lt;/sub&gt;: evidence from ARCTAS

“…We used measured concentrations of HO 2 NO 2 to calculate the contribution of HO 2 NO 2 to the XNO 2 measurement. Since the validity of the photostationary state assumption requires that the source and sink reactions of a molecule vary slowly in comparison to the lifetime of that molecule, we perform this calculation only when the lifetime of CH 3 O 2 NO 2 is less than 12 h, or there is greater than 20 h of sunlight per day as in Murphy et al (2004). Additionally, we filter the data to exclude locations where tropospheric composition has been recently perturbed.…”

“…HO 2 NO 2 dissociation is minimal and results in a median calculated NO 2 interference of less than 1 ppt (6 % of the XNO 2 signal) and a maximum absolute interference during a 1 minute period of 10.3 ppt (19 % of the NO 2 signal). This molecule is detected with near unit efficiency in the PNs channel as described previously (Murphy et al, 2004;Wooldridge et al, 2010).…”

“…Although CH 3 O 2 is the second most abundant peroxy radical in the atmosphere (after HO 2 ), much less attention has been devoted to CH 3 O 2 NO 2 chemistry. To our knowledge the indirect measurement of the sum of HO 2 NO 2 and CH 3 O 2 NO 2 during the TOPSE campaign by Murphy et al (2004) is the only previous in-situ evidence for CH 3 O 2 NO 2 . CH 3 O 2 NO 2 chemistry has been previously considered in some box and one dimensional models.…”

“…More recently, insitu observations of non-acyl peroxynitrates in the troposphere (Slusher et al, 2002;Murphy et al, 2004;Kim et al, 2007;Spencer et al, 2009) have resulted in increased interest in the role of these compounds in NO x and HO x budgets in the lower troposphere. During the NCAR Tropospheric Ozone Production about the Spring Equinox (TOPSE) experiment (Atlas et al, 2003), measurements in the Arctic upper troposphere, where temperatures were on average ∼230 K, showed that non-acyl peroxy nitrates, primarily HO 2 NO 2 , were on average, 30 % of NO y (NO y = NO + NO 2 + HO 2 NO 2 + CH 3 O 2 NO 2 + HNO 3 + HONO + acyl peroxy nitrates + organic nitrates + NO 3 + 2 N 2 O 5 ) (Murphy et al, 2004). These observations imply that HO 2 NO 2 represents a significant sink of HO x and acts as a large reservoir of NO x in the Arctic during winter and spring.…”

“…HO 2 NO 2 , CH 3 O 2 NO 2 ) are weakly bound molecules that play a role in the chemistry of the troposphere where it is cold (Slusher et al, 2002;Murphy et al, 2004;Kim et al, 2007) or where peroxy radicals and NO x (NO x = NO + NO 2 ) have especially high concentrations (Spencer et al, 2009). Initial observations and calculations focused on understanding the role these molecules play in the stratospheric HO x (HO x = OH + HO 2 ) balance (e.g.…”