The largest uncertainty in the estimation of radiative forcings on climate stems from atmospheric aerosols. In winter and summer of 2009, two periods of in-situ measurements on aerosol physical and chemical properties were conducted within the HaChi project at Wuqing, a town between Beijing and Tianjin in the North China Plain (NCP). Aerosol optical properties including scattering coefficient (&sigma;_sp), hemispheric back scattering coefficient (&sigma;_bsp), absorption coefficient (&sigma;_ap, as well as single scattering albedo (&omega;) are presented. The characteristics of diurnal and seasonal variations are analyzed together with the meteorological and satellite data. The mean values of &sigma;_{sp, 550 nm} of the dry aerosol in winter and summer are 280 &plusmn; 253 and 379 &plusmn; 251 Mm⁻¹, respectively. The average &sigma;_ap for the two periods are respectively 47 &plusmn; 38 and 43 &plusmn; 27 Mm⁻¹. The mean values of &omega; are 0.83 &plusmn; 0.05 and 0.87 &plusmn; 0.05 for winter and summer, respectively. The relative high levels of &sigma;_sp and &sigma;_bsp are representative of the regional polluted aerosol of the North China Plain. Pronounced diurnal cycle of &sigma;_sp, &sigma;_ap and &omega; are found, mainly influenced by the evolution of boundary layer and accumulation of local emissions during night-time. Regional transport of pollutants from southwest in the NCP is significant both in winter and summer, while high values of &sigma;_sp and &sigma;_ap correlate with calm winds in winter, which indicating the significant contribution of local emissions. An optical closure experiment is conducted to better understand uncertainties of the measurements. Good correlations (<i>R</i>>0.98) are found between values measured by nephelometer and values calculated with a modified Mie model. Monte Carlo simulations show an uncertainty of about 30% for the calculations. Considering all possible uncertainties of measurements, calculated &sigma;_sp and &sigma;_bsp agree well with measured values, indicating a stable performance of instruments and thus a reliable aerosol optical data

Onboard the Chinese GaoFen-5 (GF5) satellite, the Environmental trace gases Monitoring Instrument (EMI) is a nadir-viewing wide-field spectrometer that was launched on May 9, 2018. EMI measures the back-scattered earthshine solar radiance in the ultraviolet and visible spectral range. By using the differential optical absorption spectrometry (DOAS) method and the EMI measurements in the VIS1 band (405–465 nm), we performed retrievals of NO2. Some first retrieval results of NO2 from EMI and a comparison with OMI and TROPOMI products are presented in this paper. The monthly mean total vertical column densities (VCD) of NO2 show similar spatial distributions to OMI and TROPOMI (r > 0.88) and their difference is less than 27%. A comparison of the daily total VCD shows that EMI could detect the NO2 patterns in good agreement with OMI (r = 0.93) and TROPOMI (r = 0.95). However, the slant column density (SCD) uncertainty (0.79 × 1015 molec cm−2) of the current EMI algorithm is relatively larger than OMI. The daily variation pattern of NO2 from EMI in Beijing in January 2019 is consistent with TROPOMI (r = 0.96). The spatial distribution correlation of the tropospheric NO2 VCD of EMI with OMI and TROPOMI is 0.88 and 0.89, respectively, but shows an overestimate compared to OMI (15%) and TROPOMI (23%), respectively. This study demonstrates the capability of using EMI for global NO2 monitoring.