In-situ vertical characteristics of optical properties and heating rates of aerosol over Beijing

Abstract

<p><strong>Abstract.</strong> Characterizing vertical profiles of aerosol optical properties is important because only replying on the surface or column-integrated measurements is unable to unambiguously constrain the radiative impacts of aerosol. This study presents series of vertical profiles of in-situ measured multi-wavelength optical properties of aerosols during three pollution events in Nov. to Dec. 2016 over Beijing region. For all pollution events, clean periods (CP) before pollution initialization showed higher scattering Ångström exponent and smaller asymmetry parameter (<i>g</i>), and relatively uniform vertical structures. The heavy pollution (HP) periods showed increased particle size, causing these parameters to vary in the opposite way. During the transition periods (TP), regional transport of aged aerosols at upper level was found. The AERONET aerosol optical depth (AOD) matched the in-situ measurements within 10 %, however the AERONET absorption optical depth (AAOD) was 10–20 % higher than in-situ measurements, and this positive discrepancy increased to 30 % at shorter wavelength. The absorption of brown carbon (BrC) was identified by increased absorption Ångström exponent (AAE), and the heating rate of black carbon (BC) and BrC was calculated by computing the wavelength-dependent absorption coefficient and actinic flux by the radiative transfer model. BC and BrC had heating rate up to 0.18 K/h and 0.05 K/h in the planetary boundary layer (PBL) respectively during the pollution period. The fraction of BrC absorption increased from 12 % to 40 % in the PBL from CP to HP period. Notably, higher contribution of BrC heating was found above the PBL under polluted condition. This study gives a full picture of shortwave heating impacts of carbonaceous aerosols during different stages of pollution event, and highlights the increased contribution of BrC absorption especially at higher level during pollution.</p>

Multi‐Year CALIPSO Observations of Ubiquitous Elevated Aerosol Layer in the Free Troposphere Over South Asia: Sources and Formation Mechanism

“…(2019) showed a very high loading of dust particles between 3 and 7 km over the IGP and northeast India (referred as the EI in this study) during spring and summer seasons. Vertical variation of PDRs as described above could be associated with heterogeneous mixing of pure dust with anthropogenic aerosols (non‐dust aerosols) from distinct source regions due to seasonally varying wind direction (Figure 2), and hygroscopic growth of dust particles (Tian et al., 2020) particularly in summer due to high relative humidity in the FT (>60%; not shown). These result in the change of morphology and/or chemical composition, that is, the size and shape of the dust layers (Krueger et al., 2003).…”