Characteristics of aerosol chemical components and their impacts on direct radiative forcing at urban and suburban locations in Southeast Texas

The monthly/seasonal characteristics of the concentration and aerosol optical depth (AOD) of four aerosol components (water-soluble, insoluble, black carbon (BC), and sea-salt) and their direct radiative forcing (DRF) were investigated at three environmental locations in Southeast Texas. We used fine particulate matter (PM2.5) samples measured at one urban residential (Aldine (AD)) and two suburban (Deer Park (DP) and West Liberty (WL)) sites located around Houston during 2016–2017, and performed model-based analysis using the mass concentrations of the four aerosol components to evaluate their impact on the DRF. Overall, the concentrations, AODs, and DRFs of all four aerosol components at AD were higher than those at DP and WL during the study period. In particular, the water-soluble component was the most dominant contributor, except for absorbing BC. The monthly AOD patterns of the four individual aerosol components (especially, water-soluble and BC) at the three sites were found to have strong associations with their concentrations and/or relative humidity (RH). The DRFs at the top of the atmosphere (DRFTOA) and surface level (DRFSFC) for most of the aerosol components were found to be highest in winter 2017 (AD), spring 2016 and winter 2017 (DP), and winter 2016 and fall 2017 (WL). The exceptions were sea-salt and insoluble components, which showed a peak in summer 2016 and no distinct monthly variation, respectively. Uncertainties in the DRFs of the four target aerosol components calculated using in-situ RH measurements were found to be less than 20%, with the exception of the water-soluble component at WL (24%). A sensitivity test showed that the DRFs of the aerosol components were slightly and significantly influenced by changes in AOD and single scattering albedo, respectively; additionally, sensitively changed with RH. •The concentration, AOD, and DRF of aerosol components at an urban site were higher than suburban sites during 2016–2017.•The water-soluble component was the most dominant contributor, except for absorbing BC.•At the urban site (AD), the DRFs of most aerosol components were highest in winter 2017.•Their DRFs at the suburban sites were highest in spring 2016 and winter 2017 (DP) and winter 2016 and fall 2017 (WL).•The DRFs were sensitively influenced by changes in optical parameters (AOD and SSA) and RH.