Summertime impacts of Eastern Mediterranean megacity emissions on air quality

Abstract

Abstract. Megacities are large urban agglomerations with intensive anthropogenic emissions that have significant impacts on local and regional air quality. In the present mesoscale modeling study, the impacts of anthropogenic emissions from Istanbul and Athens on local and regional air quality in the Eastern Mediterranean are quantified and the responses to hypothetical decentralization scenarios applied to the extended areas of these densely populated regions are evaluated. This study focuses on summertime impacts on air quality. The results show that Athens emissions have larger regional (0.8%) and downwind (2.7% at Finokalia) impacts on O3 than Istanbul emissions that contribute to surface O3 by 0.6% to the domain-mean and 2.1% to the levels at Finokalia. On the opposite, regarding fine particle (PM2.5) levels, Istanbul emissions have larger contribution both inside the megacity itself (75%) and regionally (2.4%) compared to Athens emissions, which have a local contribution of 65% and domain-wide contribution of 0.4%. Biogenic emissions are found to limit the production of secondary inorganic aerosol species due to their impact on oxidant levels. Hypothetical decentralization plans for these urban agglomerations, maintaining the total amount of their anthropogenic emissions constant but homogeneously distributing it over larger "new" extended areas, would result in higher O3 mixing ratios inside the urban core (215% and 26% in Istanbul and Athens, respectively). On the opposite, PM2.5 concentrations would decrease by 67% and 60% in Istanbul and Athens, respectively, whereas they would increase by 10% and 11% in the rural areas of Istanbul and Athens, respectively. Concerning the "new" extended areas, Athens would experience a reduction in O3 mixing ratios by ~2% whereas Istanbul would experience an increase by ~15%. Overall decreases of PM2.5 levels by 32% and 9% are calculated over the Istanbul and Athens "new" extended areas.