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. Characterizing vertical profiles of aerosol optical properties isimportant because relying on only the surface or column-integratedmeasurements cannot unambiguously constrain the radiative impacts ofaerosol. This study presents series of vertical profiles of in situ measuredmulti-wavelength optical properties of aerosols during three pollutionevents from November to December 2016 over the Beijing region. For all pollutionevents, the clean periods (CPs) before pollution initialization showed ahigher scattering Ångström exponent (SAE) and a smaller asymmetryparameter (g) with relatively uniform vertical structures. The heavy pollution periods (HPs) showed an increased particle size, causing theseparameters to vary in the opposite way. During the transition periods (TPs),regional transport of aged aerosols at higher altitudes was found. TheAerosol Robotic Network (AERONET) aerosol optical depth (AOD) matched the in situ measurements within10 %; however the AERONET absorption optical depth (AAOD) was 10 %–20 %higher than the in situ measurements, and this positive discrepancyincreased to 30 % at shorter wavelengths. The absorption of brown carbon(BrC) was identified by the increased-absorption Ångström exponent (AAE), and the heating rate of black carbon (BC) and BrC was estimated bycomputing the spectral absorption coefficient and actinic flux calculated bya radiative transfer model. BC and BrC had a heating rate of up to 0.18 and0.05 K h−1 in the planetary boundary layer (PBL), respectively, during thepollution period. The fraction of BrC absorption increased from 12 % to40 % in the PBL from the CP to the HP. Notably, a higher contribution ofBrC heating was found above the PBL under polluted conditions. This studypaints a full picture of shortwave heating impacts of carbonaceous aerosolsduring different stages of pollution events and highlights the increasedcontribution of BrC absorption especially at higher altitudes duringpollution.

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