Abstract
Abstract. Strongly enhanced tropospheric ozone (O3) mixing ratios have been reported in the Arabian Basin, a region with intense solar radiation and high concentrations of O3 precursors such as nitrogen oxides (NOx) and volatile organic compounds (VOCs). To analyze photochemical O3 production in the marine boundary layer (MBL) around the Arabian Peninsula, we use shipborne observations of NO, NO2, O3, OH, HO2, HCHO, the actinic flux, water vapor, pressure and temperature obtained during the summer 2017 Air Quality and Climate in the Arabian Basin (AQABA) campaign, and we compare them to simulation results from the ECHAM-MESSy Atmospheric Chemistry (EMAC) general circulation model. Net O3 production rates (NOPRs) were greatest over both the Gulf of Oman and the northern Red Sea (16 ppbv d−1) and over the Arabian Gulf (32 ppbv d−1). The NOPR over the Mediterranean, the southern Red Sea and the Arabian Sea did not significantly deviate from zero; however, the results for the Arabian Sea indicated weak net O3 production of 5 ppbv d−1 as well as net O3 destruction over the Mediterranean and the southern Red Sea with values of −1 and −4 ppbv d−1, respectively. Constrained by HCHO∕NO2 ratios, our photochemistry calculations show that net O3 production in the MBL around the Arabian Peninsula mostly occurs in NOx-limited regimes with a significant share of O3 production occurring in the transition regime between NOx limitation and VOC limitation over the Mediterranean and more significantly over the northern Red Sea and Oman Gulf.
Highlights
Revenue from the exploitation of the great oil reserves in the states of and around the Arabian Peninsula has propelled remarkable economic development associated with industrialization and urbanization
During AQABA, the nitrogen oxides (NOx) mixing ratios varied over 3 orders of magnitude with the lowest values of less than 50 pptv observed in relatively pristine regions and the highest values of more than 10 ppbv found in the vicinity of areas with a strong anthropogenic influence or nearby passing ships
As average NOx is often influenced by fresh, localized emissions, we have included the median instead of the mean in the box and whiskers plot for NOx, which is less sensitive to extreme values
Summary
Revenue from the exploitation of the great oil reserves in the states of and around the Arabian Peninsula has propelled remarkable economic development associated with industrialization and urbanization. Strong population growth and the anthropogenic emission of gases and particulates over the last few decades have resulted in the Middle East becoming a hot spot for air pollution and the associated health effects; it is one of the regions worldwide where climate change is rapid (Lelieveld et al, 2016a) Unique meteorological conditions, such as intense solar radiation, high temperatures and aridity, as well as strong anthropogenic emissions of volatile organic compounds (VOCs) and nitrogen oxides (NOx=NO+NO2) from on- and offshore petrochemical industries, dense ship traffic, fossil energy production for air conditioning and desalination, and urban development are expected to further intensify in the future and contribute to photochemical ozone (O3) production (Lelieveld et al, 2009; Krotkov et al, 2016; Pfannerstill et al, 2019). Tadic et al.: Net ozone production and its relationship to NOx and VOCs tance for atmospheric chemistry studies, including the investigation of net O3 production rates (NOPRs; Monks et al, 2015; Reed et al, 2016; Bozem et al, 2017)
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