AQAST research highlights

Impacts of transported background pollutants on summertime western US air quality: model evaluation, sensitivity analysis and data assimilation
by Min Huang

M. Huang et al., Atmos. Chem. Phys., 13, 359-391, 2013

Min Huang

Estimating the impact of long-range transported pollutants on surface air quality remains a challenge. Events of transported pollution plumes (e.g., ozone and carbon monoxide) in the mid- and upper troposphere can be observed by satellites. As the plumes descend to impact the air quality in the downwind continent, they are diluted and can be difficult to distinguish, especially in receptor regions with strong local production and complex topography.  The paper by Huang et al. (2013) discusses important factors affecting the model-estimated transported background (TBG) contribution (indicating the impacts from extra-regional sources) to ozone in the western US during the NASA-ARCTAS period. Uncertainties are mainly associated with the regional model boundary conditions and the model resolution, and weakly with local anthropogenic emissions. The paper also assesses how data assimilation of measurements from the current observing systems can improve the modeled total O3 and TBG contribution during a long-range transport episode. The mechanisms that determine TBG contributions and their variation are analyzed by calculating metrics to quantify the probability of airmasses originating from certain locations entraining into the boundary layer. Receptor-based adjoint sensitivity analysis is also used to demonstrate the connection between surface O3 and O3 aloft 1–2 days earlier. This study answers important science questions related to the contribution of distant sources to US air quality and contributes to the activities of the international Task Force on Hemispheric Transport of Air Pollution (TH HTAP).

Jan 2013