Measurements of carbonyl compounds around the Arabian Peninsula: overview and model comparison

Abstract

Abstract. Volatile organic compounds (VOCs) were measured around the Arabian Peninsula using a research vessel during the AQABA campaign (Air Quality and Climate Change in the Arabian Basin) from June to August 2017. In this study we examine carbonyl compounds, measured by a proton transfer reaction mass spectrometer (PTR-ToF-MS), and present both a regional concentration distribution and a budget assessment for these key atmospheric species. Among the aliphatic carbonyls, acetone had the highest mixing ratios in most of the regions traversed, varying from 0.43 ppb over the Arabian Sea to 4.5 ppb over the Arabian Gulf, followed by formaldehyde (measured by a Hantzsch monitor, 0.82 ppb over the Arabian Sea and 3.8 ppb over the Arabian Gulf) and acetaldehyde (0.13 ppb over the Arabian Sea and 1.7 ppb over the Arabian Gulf). Unsaturated carbonyls (C4–C9) varied from 10 to 700 ppt during the campaign and followed similar regional mixing ratio dependence to aliphatic carbonyls, which were identified as oxidation products of cycloalkanes over polluted areas. We compared the measurements of acetaldehyde, acetone, and methyl ethyl ketone to global chemistry-transport model (ECHAM5/MESSy Atmospheric Chemistry – EMAC) results. A significant discrepancy was found for acetaldehyde, with the model underestimating the measured acetaldehyde mixing ratio by up to an order of magnitude. Implementing a photolytically driven marine source of acetaldehyde significantly improved the agreement between measurements and model, particularly over the remote regions (e.g. Arabian Sea). However, the newly introduced acetaldehyde source was still insufficient to describe the observations over the most polluted regions (Arabian Gulf and Suez), where model underestimation of primary emissions and biomass burning events are possible reasons.

Impact of pyruvic acid photolysis on acetaldehyde and peroxy radical formation in the boreal forest: theoretical calculations and model results

“…Wang et al (2020) reported CH 3 CHO mixing ratios that were up to a factor of 10 higher than predicted by a global chemistry-transport model (EMAC) in the marine boundary layer around the Arabian Peninsula, implying missing sources of CH 3 CHO in remote and polluted regions. Wang et al (2019) also found that models systematically underestimate CH 3 CHO compared to observations, implying a missing source of acetaldehyde in the remote troposphere. This finding was supported by the simultaneous measurement of peracetic acid (which is formed, for example, via the degradation of acetaldehyde in remote environments) with the organic aerosol source of CH 3 CHO also being insufficient to explain the results.…”

“…Global models have recently revealed discrepancies between simulated and measured acetaldehyde concentrations (Millet et al, 2010;Wang et al, 2019;Wang et al, 2020). Wang et al (2020) reported CH 3 CHO mixing ratios that were up to a factor of 10 higher than predicted by a global chemistry-transport model (EMAC) in the marine boundary layer around the Arabian Peninsula, implying missing sources of CH 3 CHO in remote and polluted regions.…”

“…This finding was supported by the simultaneous measurement of peracetic acid (which is formed, for example, via the degradation of acetaldehyde in remote environments) with the organic aerosol source of CH 3 CHO also being insufficient to explain the results. Instead, Wang et al (2019) suggested that CH 3 CHO arises from the degradation of gas-phase organic compounds. Pyruvic acid, among other organic acids in the gas and aerosol phase, might be one of the compounds that can be converted to acetaldehyde in the remote troposphere, and its integration into global models might contribute to resolve discrepancies, especially in forested regions.…”

Comment on acp-2021-79

“…H 2 O 2 mixing ratios were measured via dual-enzyme detection (modified AEROLASER AL2021, Garmisch-Partenkirchen, Germany) with a total measurement uncertainty of 9 % and a detection limit of 15 ppt v (Hottmann et al, 2020). DMS was measured via proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS-8000, Ionicon Analytik GmbH, Innsbruck, Austria) with a detection limit of 15 ppt v (Wang et al, 2020;Edtbauer et al, 2020). CH 3 I was measured with a custom-built fast gas chromatography -mass spectrometry system described by Bourtsoukidis et al (2017) with a detection limit of 0.5 ppt v .…”

Measurement report: In situ observations of deep convection without lightning during the tropical cyclone Florence 2018

“…Analytik GmbH, Innsbruck, Austria) with a detection limit of 15 ppt v (Wang et al, 2020;Edtbauer et al, 2020). CH 3 I was measured with a custom-built fast gas chromatography -mass spectrometry system described by Bourtsoukidis et al (2017) with a detection limit of 0.5 ppt v .…”