Aging and removal of Black Carbon measured using a Single Particle Soot Photometer in East Asia

Abstract:

Black carbon (BC) aerosol is one of the most important aerosols, affecting the Earth’s radiative budget both directly through light absorption and indirectly by acting as cloud condensation and ice nuclei. Microphysical parameters of soot aerosols are important to assess their roles in atmosphere. A single particle soot photometer (SP2, Droplet Measurement Technologies Inc.) can be used to detect and quantify the mass of refractory BC (rBC) in a soot-containing particle. We conducted ground-measurements of rBC-containing particles using the SP2 at Yokosuka (near industrial sources, early summer of 2014, Fig1) and at Fukue island (outflow from Asian continent, spring of 2015, Fig1). During Fukue observation, we measured carbon monoxide (CO) mixing ratio (by 48C, Themo Scientific, Inc.) which is useful for investigating polluted air masses. Air mass histories were analyzed with backward trajectories from the sampling point and precipitation along the trajectory calculated using the NOAA Hybrid Single-Particle Lagrangian Integrated Trajectory model with the meteorological data sets from NCEP’s GDAS. We analysed number-/mass-size distributions and mixing states of rBC-containing particles considering the differences in air mass characteristics and history. The observed rBC mass concentrations (at STP) were ranging from ~50 ng m^-3 at Fukue island to ~2000 ng m^-3 near industrial sources. The size distributions of rBC-containing particles were systematically changed depending on the sites and air mass histories. Modal mass-equivalent diameters of the observed mass-size distributions showed minima (~0.16 μm) near source area and maxima (~0.21 μm) at Fukue island for Asian outflow period without wet removal. In the presentation, we synthetically discuss the relationship between rBC microphysics and air mass characteristics and histories.