Formaldehyde and hydroperoxide distribution around the Arabian Peninsula – evaluation of EMAC model results with ship-based measurements

[摘要] Formaldehyde (HCHO), hydrogen peroxide (H 2 O 2 )and organic hydroperoxides (ROOH) play a key role in atmospheric oxidationprocesses. They act as sources and sinks for HO x radicals(OH  +  HO 2 ), with OH as the primary oxidant that governs theatmospheric self-cleaning capacity. Measurements of these species allowfor evaluation of chemistry-transport models which need to account formultifarious source distributions, transport, complex photochemical reactionpathways and deposition processes of these species. HCHO is an intermediateduring the oxidation of volatile organic compounds (VOCs) and is an indicator of photochemical activityand combustion-related emissions. In this study, we use in situ observationsof HCHO, H 2 O 2 and ROOH in the marine boundary layer (MBL) toevaluate results of the general circulation model EMAC (ECHAM5/MESSy2Atmospheric Chemistry; European Center HAMburg, Modular Earth Submodel System). The dataset was obtained during the Air Quality and Climate Change in the Arabian Basin (AQABA) shipcampaign around the Arabian Peninsula in summer 2017. This region ischaracterized by high levels of photochemical air pollution, humidity andsolar irradiation, especially in the areas around the Suez Canal and theArabian Gulf. High levels of air pollution with up to 12 ppbv HCHO, 2.3 ppbvROOH and relatively low levels of H 2 O 2 ( ≤0.5  ppbv) weredetected over the Arabian Gulf. We find that EMAC failed to predict absolutemixing ratios of HCHO and ROOH during high-pollution events over the ArabianGulf, while it reproduced HCHO on average within a factor of 2. Drydeposition velocities were determined for HCHO and H 2 O 2 atnight with 0.77±0.29  cm s −1 for HCHO and 1.03±0.52  cm s −1 for H 2 O 2 over the Arabian Sea, which werematched by EMAC. The photochemical budget of H 2 O 2 revealedelevated HO x radical concentrations in EMAC, which resulted in anoverestimation of H 2 O 2 by more than a factor of 5 for the AQABAdataset. The underestimated air pollution over the Arabian Gulf was relatedto EMAC's coarse spatial resolution and missing anthropogenic emissions inthe model.

[学科分类] 医学（综合）