<p>Volatility and hygroscopicity properties of atmospheric particles with dry sizes of 60 and 145 nm were measured by using a Volatility-Hygroscopicity Tandem Differential Mobility Analyzer (VH-TDMA) at a suburban site over the Pearl River Delta region in China during the late summer of 2016. Specifically, volatility properties of the aerosols were studied by heating the ambient samples step-wise to seven temperatures ranging from 30 to 300&#8451;. In general, particles started to evaporate at the heating temperature of 100&#8451;. After heating the aerosols above 200&#8451;, the probability density function of the volatility growth factor showed an apparent bimodal distribution with a distinct non-volatile mode and a volatile mode, indicating that the particle population was mainly externally mixed. Even at 300&#8451;, around 20% of the aerosol volume still remained in the particle phase (non-volatile material). Black carbon (BC) mass fraction of aerosol mass correlated well (R<sup>2</sup>&#8776; 0.5) with the volume fraction remaining (VFR) at 300&#8451;, but could not explain the non-volatile residual alone. On the basis of the comparison analysis between the VFR at different temperatures and the hygroscopic growth factor (HGF) at 90% RH, we observed the non-volatile residual material were hygroscopic (HGF=1.45). These results indicate that the observed non-volatile residual material at 300&#8451; did not consist solely of black carbon, but some other compounds such as sea salt, low-volatile ammonium or organic polymer.</p>
Black carbon measurements in the Pearl River Delta region of China
