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Determining background aerosol optical depth threshold value (BAOD) is critical to aerosol type identification and air pollution control. This study presents a statistical method to select the best BAOD threshold value using the VIIRS DB AOD products at 1 × 1 degree resolution from 2012 to 2019 as a major testbed. A series of multiple lognormal distributions with 1 to 5 peaks are firstly applied to fit the AOD histogram at each grid point, and the distribution with the highest correlation coefficient (R) gives preliminary estimations of BAOD, which is defined as either the intersection point of the first two normal distribution curves when having multiple peaks, or the midpoint between the peak AOD and the first AOD with non-zero probability when the mono peak is the best fit. Then, the lowest 1st to 100th percentile AOD distributions are compared with the preliminary BAOD distribution on a global scale. The final BAOD is obtained from the best cutoff percentile AOD distributions with the lowest bias compared with preliminary BAOD. Results show that the lowest 30th percentile AOD is the best estimation of BAOD for different AOD datasets and different seasons. Analysis of aerosol chemical information from MERRA-2 further supports this selection. Based on the BAOD, we updated the VIIRS aerosol type classification scheme, and the results show that the updated scheme is able to achieve reliable detection of aerosol type change in low aerosol loading conditions. [ABSTRACT FROM AUTHOR]

We analyze the long-term variations in the microstructural characteristics of aerosol in the surface air layer measured in the monitoring mode at the Aerosol Station of V.E. Zuev Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, in 2000–2020. Estimates are carried out based on the following characteristics: the concentrations of submicron Nf and coarse Nc particles and their ratio Nf /Nc. Two datasets are considered: "total" and separately for the "background" type of the "aerosol weather." The variability range of the annual average values of the total concentration of particles N(r > 0.2 μm) is found to be 8–50 cm−3, and the aerosol concentrations for the background situations is 5–30 cm−3. No reliable long-term trends in the characteristics under study are revealed. Spectral analysis of the monthly average concentrations for the background dataset showed the presence of a significant (with the 0.95 probability) time period of about a year for Nf /Nc and Nf and its absence for Nc. [ABSTRACT FROM AUTHOR]

This work is intended to study the effect of background particles on vehicle emissions in representative realistic atmospheric environments. The coupling of Reynolds-Averaged Navier–Stokes equation (RANS) and Taylor-series Expansion Method Of Moments (TEMOM) is performed to track the emissions of the vehicle and simulating the evolution of the matters. The transport equation of mass, momentum, heat, and the first three orders of moments are taken into account with the effect of binary homogeneous nucleation, Brownian coagulation, condensation, and thermophoresis. The parameterization model is utilized for nucleation. The measured data for Beijing's particle size distribution under both polluted and nonpolluted conditions are utilized as background particles. The relationship between the macroscopic measurement results and the microscopic dynamic process is analyzed by comparing the variation trend of several physical quantities in the process of aerosol evolution. It is found with an increase of background particle concentration, the nucleation is inhibited, which is consistent with the existing studies. [ABSTRACT FROM AUTHOR]

We investigate the use of multiple scattering via Multiple-Field-Of-View (MFOV) lidar signals to characterize bioaerosol particles size and concentration from ground based lidar over distances shorter than a few kilometers. The MFOV lidar signal is calculated for background aerosols at a wavelength 355 nm for a visibility of 30 km. The optical depths studied are small and the calculations are restricted to second order scattering. Also since background aerosols are constituted of relatively small particles which diffuse the light at large angles, the fields of view (FOV) range from 1 to 100 mrad full angle. We show that the MFOV lidar measurements contain exploitable information on particle size and extinction. [ABSTRACT FROM AUTHOR]

Measurements of carbonyl sulfide (COS) and carbondisulfide (CS) were carried out on samples drawn from a smoke stack of an aluminium smelter. Volume mixing ratios of 6 ppm COS and 0.1 ppm CS were measured for gases from the electrolysis unit that had previously passed an AlO fluid bed reactor and electrostatic precipitators. Specific emissions of 1.6 kg COS and 0.03 kg CS per ton of primary aluminium were found. Extrapolating from this particular smelter's conditions to a world mix specific COS emissions of about 4 kg/t(Al) are calculated resulting in emissions of annually 0.08 Tg COS into the atmosphere due to electrolytic aluminium production in 1995. Besides the photochemical conversion of anthropogenic CS aluminium production is established to be the second major industrial source of COS probably exceeding automotive tire wear's and coal combustion's contributions. [ABSTRACT FROM AUTHOR]