Assessment of Air Pollution in the Middle East Using Reanalyses Products and High-resolution WRF-Chem Simulations
<p>The Middle East is notorious for high air pollution that affects both air-quality and regional climate. The Middle East generates about 30% of world dust annually and emits about 10% of anthropogenic SO<sub>2</sub>. In this study we use Modern-Era Retrospective analysis for Research and Applications v.2 (MERRA-2), Copernicus Atmosphere Monitoring Service Operational Analysis (CAMS-OA) data assimilation products, and a regional Weather Research and Forecasting model (10 km resolution) coupled with Chemistry (WRF-Chem) to evaluate natural and anthropogenic air pollution in the ME. The SO<sub>2</sub> anthropogenic emissions used in WRF-Chem are updated using the independent satellite SO<sub>2</sub> emission dataset obtained from the Ozone Monitoring Instrument (OMI) observations onboard NASA EOS Aura satellite. Satellite and ground-based aerosol optical depth (AOD) observations, as well as Particulate Matter (PM) and SO<sub>2</sub> in situ measurements for 2015-2016, were used for validation and model evaluation.&#160;</p><p>Although aerosol fields in regional WRF-Chem and global assimilation products are quite consistent, WRF-Chem, due to its higher spatial resolution and novel OMI SO<sub>2</sub> emissions, is preferable for analysis of regional air-quality over the ME. We found that conventional emission inventories (EDGAR-4.2, MACCity, and HTAP-2.2) have uncertainties in the location and magnitude of SO<sub>2</sub> sources in the ME and significantly underestimate SO<sub>2</sub> emissions in the Arabian Gulf. CAMS reanalysis tends to overestimate PM<sub>2.5</sub> and underestimate PM<sub>10</sub> concentrations. In the coastal areas, MERRA2 underestimates sulfate and tends to overestimate sea salt concentrations. The WRF-Chem&#8217;s PM background concentrations exceed the World Health Organization (WHO) guidelines over the entire ME. The major contributor to PM (~75&#8211;95%) is mineral dust. In the ME urban centers and near oil recovery fields, non-dust aerosols (primarily sulfate) contribute up to 26% into PM<sub>2.5</sub>. The contribution of sea salt into PM can rich up to 5%. The contribution of organic matter into PM prevails over black carbon. SO<sub>2</sub> surface concentrations in major ME cities frequently exceed European air-quality limits.</p>