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 properties of summer radiation and aerosols were studied at Xinzhou, a suburban site on the North China Plain (NCP) by using ground-based measurements in 2014. The radiation detections under clear and cloudy skies showed that longwave radiation presented a sigmate pattern, with a maximum of 392.6 W m(-2) at 1700 local standard time (LST) associated with the cloud radiative forcing, and a minimum of 360.0 W m(-2) at 0600 LST when the lowest surface temperature (17.1 degrees C) occurred. Solar radiation, including global, direct, diffuse, photosynthetically active, ultraviolet-A, and ultraviolet-B, exhibited a single peak at similar to 1300 LST. A bimodal size distribution, with fine mode aerosols showing a peak between 0.1 and 0.2 mu m and coarse mode aerosols showing a peak at similar to 5 mu m, was observed at Xinzhou. The dominant aerosol type was black carbon coating on coarse particles (85.7%) for the cases with aerosol optical depth at 400 nm (AOD) greater than 0.4, leading to a lower single scattering albedo (0.81) than the typical value (similar to 0.90) at the other stations on the NCP. The mean values of EAE and AAE (extinction and absorption angstrom ngstrom exponent, respectively) were 1.14 +/- 0.15 and 0.58 +/- 0.28 for the aerosol measurements. The average of instantaneous aerosol direct radiative forcing at the bottom of the atmosphere was -138.9 +/- 33.0 W m(-2)for the cases with AOD > 0.4. The results in this study are expected to improve understanding at suburban sites on the NCP of aerosol properties and their impacts on regional radiation budgets.