Abstract
Abstract. A Single Particle Aerosol Mass Spectrometer (SPAMS), a Single Particle Soot Photometer (SP2) and various meteorological instruments were employed to investigate the chemical and physical properties of black carbon (BC) aerosols during a regional air pollution episode in urban Shanghai over a 5-day period in December 2013. The refractory black carbon (rBC) mass concentrations measured by SP2 averaged 3.2 µg m−3, with the peak value of 12.1 µg m−3 at 04:26 LT on 7 December. The number of BC-containing particles captured by SPAMS in the size range 200–1200 nm agreed very well with that detected by SP2 (R2 = 0.87). A cluster analysis of the single particle mass spectra allowed for the separation of BC-containing particles into five major classes: (1) Pure BC; (2) BC attributed to biomass burning (BBBC); (3) K-rich BC-containing (KBC); (4) BC internally mixed with OC and ammonium sulfate (BCOC-SOx); (5) BC internally mixed with OC and ammonium nitrate (BCOC-NOx). The size distribution of internally mixed BC particles was bimodal. Detected by SP2, the condensation mode peaked around ∼ 230 nm and droplet mode peaked around ∼ 380 nm, with a clear valley in the size distribution around ∼ 320 nm. The condensation mode mainly consisted of traffic emissions, with particles featuring a small rBC core (∼ 60–80 nm) and a relatively thin absolute coating thickness (ACT, ∼ 50–130 nm). The droplet mode included highly aged traffic emission particles and biomass burning particles. The biomass burning particles had a larger rBC core (∼ 80–130 nm) and a thick ACT (∼ 110–300 nm). The highly aged traffic emissions had a smaller core (∼ 60–80 nm) and a very thick ACT (∼ 130–300 nm), which is larger than reported in any previous literature. A fast growth rate (∼ 20 nm h−1) of rBC with small core sizes was observed during the experiment. High concentrations pollutants like NO2 likely accelerated the aging process and resulted in a continuous size growth of rBC-containing particles from traffic emission.
Highlights
Aerosols represent the largest uncertainty in estimating radiative forcing of atmospheric species, by strongly affecting the energy balance of the Earth by scattering and/or absorbing solar radiation (Pöschl, 2005), and influencing cloud formation (Jacobson, 2006)
The Aquadag® black carbon particles were selected by mobility diameter using a differential mobility analyzer (DMA) and the corresponding particle masses were calculated using the effective density data provided in Gysel et al (2011) (Fig. S1 in the Supplement)
Pure black carbon (BC) Biomass Burning BC-containing (BBBC) K-rich BC-containing (KBC) BC internally mixed with OC and ammonium nitrate (BCOC-NOx ) BC internally mixed with OC and ammonium sulfate (BCOC-SOx ) Unidentified Total BC-containing
Summary
Aerosols represent the largest uncertainty in estimating radiative forcing of atmospheric species, by strongly affecting the energy balance of the Earth by scattering and/or absorbing solar radiation (Pöschl, 2005), and influencing cloud formation (Jacobson, 2006). SP2 can quantitatively measure the mass and determine the mixing state of an individual rBC-containing particle (Schwarz et al, 2010). As a highly complementary instrument, single particle aerosol mass spectrometer (SPAMS, not to be confused with the SP-AMS instrument mentioned above) can detect the chemical properties of BC particles. All of the studies mentioned above relied on either an SP2 instrument or a single particle aerosol mass spectrometer to characterize BC particles, but not both Combining these two methods would provide the chemical and physical prosperities of individual BC particles simultaneously and greatly enhance our understanding of their sources and evolution processes. We used an SP2 instrument to measure the mass and size distribution, and the mixing state of individual rBC particles. A SPAMS instrument was used in parallel to record chemical characteristics and mixing state of individual BC particles
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