Gas Phase Air Pollution in Remote and Urban Atmospheres: From the Azores to Beijing

Gaseous air pollutants can be hazardous to health and contribute to global warming, both directly or via the formation of particulate matter. Understanding atmospheric composition in both remote and urban regions is essential for understanding air pollution and developing methods for mitigating its harmful impacts. In this thesis, measurements of gas-phase pollutants are presented in Beijing, China and over the North Atlantic. Despite being very different, both these atmospheres are polluted. Seasonal differences in air pollution are examined for Beijing comparing measurements made during November–December 2016 and May–June 2017. Meteorology significantly impacts the winter pollution experienced as periods of stagnant weather allow pollution to build up leading to haze events. High O3 mixing ratios were measured in summertime, with a daytime average of 66.4 ppbv. Large deviations from the O3-NO-NO2 photostationary state are presented which cannot be explained solely by the presence of peroxy radicals. Seasonal differences in emissions were also explored. For the first time in Beijing, the eddy-covariance technique was used to quantify emissions of NOx, CO and aromatic VOCs with traffic found to be the dominant source. NOx and CO fluxes were then compared to a Chinese emissions inventory, which significantly overestimated emissions for the region, suggesting that proxy-based emissions inventories have positive biases in urban centres. This work provides a useful benchmark of emissions from the city which can help to inform future inventories. The spatial distribution of gas-phase pollutants over the North Atlantic Ocean is explored and it is shown that transport of pollutants from North America impact the atmospheric composition of the region. Measurements were then compared with the GEOS-Chem model which highlighted a systematic underestimation in CO mixing ratios by the model, possibly indicating a missing source of emissions in the inventory used.