1 research outputs found
Real-Time Characterization of Aerosol Particle Composition above the Urban Canopy in Beijing: Insights into the Interactions between the Atmospheric Boundary Layer and Aerosol Chemistry
Despite
extensive efforts into the characterization of air pollution
during the past decade, real-time characterization of aerosol particle
composition above the urban canopy in the megacity Beijing has never
been performed to date. Here we conducted the first simultaneous real-time
measurements of aerosol composition at two different heights at the
same location in urban Beijing from December 19, 2013 to January 2,
2014. The nonrefractory submicron aerosol (NR-PM<sub>1</sub>) species
were measured in situ by a high-resolution aerosol mass spectrometer
at near-ground level and an aerosol chemical speciation monitor at
260 m on a 325 m meteorological tower in Beijing. Secondary aerosol
showed similar temporal variations between ground level and 260 m,
whereas much weaker correlations were found for the primary aerosol.
The diurnal evolution of the ratios and correlations of aerosol species
between 260 m and the ground level further illustrated a complex interaction
between vertical mixing processes and local source emissions on aerosol
chemistry in the atmospheric boundary layer. As a result, the aerosol
compositions at the two heights were substantially different. Organic
aerosol (OA), mainly composed of primary OA (62%), at the ground level
showed a higher contribution to NR-PM<sub>1</sub> (65%) than at 260
m (54%), whereas a higher concentration and contribution (15%) of
nitrate was observed at 260 m, probably due to the favorable gas–particle
partitioning under lower temperature conditions. In addition, two
different boundary layer structures were observed, each interacting
differently with the evolution processes of aerosol chemistry