Impact of acetone (photo)oxidation on HO_xproduction in the UT/LMS based on CARIBIC passenger aircraft observations and EMAC simulations

Abstract

Until a decade ago, acetone was assumed to be a dominant HO x source in the dry extra-tropical upper troposphere (ex-UT). New photodissociation quantum yields of acetone and the lack of representative data from the ex-UT challenged that assumption. Regular mass spectrometric observations onboard the Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC) passenger aircraft deliver the first representative distribution of acetone in the UT/LMS (UT/lowermost stratosphere). Based on diverse CARIBIC trace gas data and non-observed parameters taken from the model ECHAM5/MESSy for Atmospheric Chemistry, we quantify the HO x source in the UT/LMS from (photo)oxidation of acetone. The findings are contrasted to HO x production from ozone photolysis, overall the dominant tropospheric HO x source. It is shown that HO x production from acetone (photo)oxidation reaches up to 95% of the HO x source from ozone photolysis in autumn in the UT and on average~61% in summer. That is, acetone is a significant source of HO x in the UT/LMS.

Measurements of CH<sub>3</sub>O<sub>2</sub>NO<sub>2</sub> in the upper troposphere

“…This is lower than the values observed in the upper troposphere at ambient temperatures less than 230 K. Even though the temperatures in the lower stratosphere are low enough for the CH 3 O 2 NO 2 lifetime to be greater than 10 h, the observations of CH 3 O 2 NO 2 indicate that the lower stratosphere has lower mixing ratios of the precursors of CH 3 O 2 needed to form CH 3 O 2 NO 2 . These include the peroxy acyl radical from acetaldehyde, which reacts with NO to produce CH 3 O 2 (e.g., Tyndall et al, 2001), and CH 3 COCH 3 , which can photolyze to produce CH 3 O 2 (e.g., Folkins and Chatfield, 2000;Jaeglé et al, 2001;Neumaier et al, 2014).…”

Air‐sea exchange of methanol and acetone during HiWinGS: Estimation of air phase, water phase gas transfer velocities

“…Second in abundance amongst organic gases in the global atmosphere after methane, methanol is a precursor to carbon monoxide [ Duncan et al ., ] and formaldehyde [ Millet et al ., ]. Acetone is a precursor to the pollutant peroxyacetyl nitrate (PAN) as well as a significant source of HO x in the dry upper troposphere [ Singh et al ., ; Neumaier et al ., ]. According to the synthesis by Heald et al .…”

An emission module for ICON-ART 2.0: implementation and simulations of acetone

“…Due to the seasonal variability in the biogenic emissions of acetone, its VMR in the mid-latitude UTLS region shows a seasonal cycle with maximum values above 1500 pptv during summer (Sprung and Zahn, 2010;Elias et al, 2011;Neumaier et al, 2014). This is shown in Fig.…”

“…HO x can deplete ozone so that VOCs have climatic impact in the UTLS region (e.g. Neumaier et al, 2014). In this study, we will focus on the influence of acetone which is together with methanol one of the most abundant VOC in the UTLS region.…”

“…In this study, we will focus on the influence of acetone which is together with methanol one of the most abundant VOC in the UTLS region. Mixing ratios of 300-2000 pptv (1 pptv = 10 −12 mol mol −1 ) have been observed in the Northern Hemisphere mid-latitudes (Singh et al, 1995;Jaeglé et al, 1998;Heikes et al, 2002;Sprung and Zahn, 2010;Elias et al, 2011;Neumaier et al, 2014).…”