Sources of tropospheric ozone over Europe and East Asia

Abstract

Tropospheric ozone is an important greenhouse gas and air pollutant that is harmful to human health and ecosystems. Emissions from land transport and other anthropogenic sources, such as industry, are significant contributors of nitrogen oxides (NOx), carbon monoxide, and volatile organic compounds (VOC). These serve as important precursor substances for tropospheric ozone and influence air quality. Due to the nonlinear ozone chemistry, directly calculating the contribution of emission sectors to ozone is not possible. For this purpose, detailed chemistry-climate models are required. In my dissertation, I examine the contributions of different emission sectors to ground-level ozone in Europe and East Asia. I utilise the MECO(n) model system, which comprises a global and regional model. The latter allows for high-resolution analysis of specific regions. The model employs a tagging method to calculate the contributions of various emission sources to ozone. Two simulations, each with two regional refinements for Europe and East Asia, are conducted over a span of 2 years, at resolutions of 50 and 12 km. The model results are evaluated using satellite data, air quality station data, data from two flight campaigns in Europe and Asia, and ship-based MAX-DOAS measurements over the Chinese Sea. Several regions in Europe and East Asia with large anthropogenic emissions are compared with one another, as well as with rural areas. The absolute contributions of regional anthropogenic emissions to ground-level ozone in the Po Valley, with 20 nmol mol-1 (31 %), are larger than in the Benelux region, with 9 nmol mol-1 (22 %), for the summer of 2017-2018. Similar results are found for East Asia, where the Pearl River Delta, Yangtze River Delta, and Sichuan Basin exhibit the largest contributions of regional anthropogenic emissions to ground-level ozone, ranging from 25-40 nmol mol-1 (46-49 %). In some coastal and rural areas of Europe and East Asia, long- range transport contributions to ozone are more important than regional anthropogenic emissions. In heavily polluted regions of Europe and East Asia, ozone titration is large and ozone production is inefficient. In these areas, ozone production is limited by VOCs. In most basins and rural locations, ozone production is rather efficient and NOx-limited. The Po Valley in Europe and the Pearl River Delta in East Asia have the largest mitigation potential for ground-level ozone by reducing local anthropogenic NOx and VOC sources, respectively. The effect of different representations of emissions with large uncertainties, such as from biomass burning and biogenic VOCs, on the ozone contributions from anthropogenic emission sources is almost negligible.