Investigating the regional contributions to air pollution in Beijing: A dispersion modelling study using CO as a tracer

The rapid urbanization and industrialization of Northern China in recent decades has resulted in poor air quality in major cities like Beijing. Transport of air pollution plays a key role in understanding the relative influence of local emissions and regional contributions to observed air pollution. In this study, a combination of dispersion modelling (Numerical Atmospheric Modelling Environment, NAME model) with emission inventories and in-situ ground measurement data are used to track the air mass pathways arriving at Beijing. The percentage of time the air masses spent over specific regions on their travel to Beijing is used to assess the effects of regional meteorology on carbon monoxide (CO) levels. The NAME model is used with the MEIC (Multi-resolution Emission Inventory) 2013 emission inventories to determine the amount of pollution that is transported to Beijing from the immediate surrounding areas and regions further away. This technique captures the magnitude and variability of CO over Beijing revealing that CO is strongly driven by transport processes. This study provides a more detailed understanding of relative contributions to air pollution in Beijing under different regional airflow conditions. Emission inventories and NAME show that approximately 45% of the total CO pollution that affects Beijing is transported from other regions. Furthermore, it was determined that approximately half of the regional contribution is transported from areas that immediately surround Beijing (i.e. Hebei and Tianjin) and the rest from areas further away. Last but not least, using PM_2.5, three contribution cases were identified and discussed. The results can inform targeted control measures to be implemented by Beijing and the surrounding provinces to tackle air quality problems that affects Beijing and China.