“…For example, fixed site monitors are sparse in much of the western US, and satellite products do not provide surface-level concentrations on their own. Atmospheric model simulations may be biased by their emission inventories (Davis et al, 2015;Zhang et al, 2014), spatial resolution (Misenis and Zhang, 2010;Punger and West, 2013;Thompson et al, 2014;Thompson and Selin, 2012), or input meteorological fields (Cuchiara et al, 2014;Srinivas et al, 2015;Žabkar et al, 2013). Thus, there is a growing effort to include multiple datasets (e.g., Henderson et al, 2011;Yao et al, 2013) and create blended products that can exploit the strengths of each dataset (Brauer et al, 2015;Lassman et al, 2017;Gan et al, 2017;Reid et al, 2015;Yao and Henderson, 2014).…”