A study of aerosol properties based on observations of particulate matter from the U.S. Embassy in Beijing, China

The United States Embassy in Beijing, China, released publicly a record of mass concentrations of particulate matter 2.5 µm and smaller in aerodynamic diameter (PM2.5) from April 2008 to the present measured with a Beta Attenuation Monitor (BAM). We compare these measurements with observations of particulate matter recorded at the Beijing Institute of Atmospheric Physics and observations of visibility recorded at the Beijing Capital International Airport (BCIA) to assess their value as a record of air quality in the greater Beijing metropolitan area. We find that the PM2.5 observations correlate well with the other observations of PM over the period January 1st to February 1st 2013 using a Tapered Element Oscillating Microbalance and an Aerosol Mass Spectrometer (AMS), and they exhibit a clear inverse correlation with visibility measured at BCIA. Using inverse visibility as a proxy of radiation extinction, we determine a dry mass extinction efficiency and a dependence of radiation extinction to relative humidity that is consistent with other studies of polluted urban environments. We deduce a strong degree of homogeneity of particulate pollution across the Beijing metropolitan region and conclude that the U.S. Embassy measurements are a reliable sample of this particulate pollution during periods of photochemical smog. The U.S. Embassy observations of PM2.5 appear to remain consistent throughout the available record and can serve as a useful dataset for studying future trends in particulate matter as China implements ambitious measures to improve air quality in the region.