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The spatiotemporal distribution and characterization of aerosol optical properties in the north of Vietnam were investigated extensively using the long-term measurements obtained from Moderate Resolution Imaging Spectroradiometer (MODIS) (from 2010 to 2019) and two Aerosol Robotic Network (AERONET) stations (Nghia Do, Hanoi City, from 2010 to 2019 and Son La from 2012 to 2019) located in fast-developing urban areas. This study also analyzed the tendency of AOD over different wavelengths as well as the influences of meteorological parameters and boundary layer height (BLH) on AOD and Ångström exponent (AE). The annual mean AOD500 at Nghia Do and Son La stations were 0.81 and 0.78, respectively. Our results revealed the existence of particles emitted from anthropogenic activities in Hanoi and Son La with the dominance of fine particles (more than 90% of the AE440–870 were larger than 1). Besides, a high percentage of AE440–870 larger than or approximately 1.5 during the dry and transition months in Son La indicated the existence of biomass-burning aerosol particles due to forest fires and burning of agriculture residuals. The classification results for aerosol types showed the presence of both biomass burning and urban/industrial aerosol types at Nghia Do and Son La sites. Among the investigated meteorological parameters, surface solar radiation expressed a significant correlation with AE440–870 in all three seasons at the two sites due to the secondary formation of fine particles induced by the high solar radiation condition. The impacts of meteorological parameters and BLH on AOD were not observed simultaneously during three seasons at Nghia Do and Son La stations. [ABSTRACT FROM AUTHOR]

Based on multiple linear regression (MLR) models, we estimated the PM2.5 at Seoul using a number of aerosol optical depth (AOD) values obtained from ground-based and satellite remote sensing observations. To construct the MLR model, we consider various parameters related to the ambient meteorology and air quality. In general, all AOD values resulted in the high quality of PM2.5 estimation through the MLR method: mostly correlation coefficients >~0.8. Among various polar-orbit satellite AODs, AOD values from the MODIS measurement contribute to better PM2.5 estimation. We also found that the quality of estimated PM2.5 shows some seasonal variation; the estimated PM2.5 values consistently have the highest correlation with in situ PM2.5 in autumn, but are not well established in winter, probably due to the difficulty of AOD retrieval in the winter condition. MLR modeling using spectral AOD values from the ground-based measurements revealed that the accuracy of PM2.5 estimation does not depend on the selected wavelength. Although all AOD values used in this study resulted in a reasonable accuracy range of PM2.5 estimation, our analyses of the difference in estimated PM2.5 reveal the importance of utilizing the proper AOD for the best quality of PM2.5 estimation. [ABSTRACT FROM AUTHOR]

• The ASoRA method estimates the atmospheric attenuation in a tower CSP. • The atmospheric attenuation occurs in the atmospehric column and in the slant path. • ASoRA is validated with data observed at Ouarzazate, Morocco. • The aerosols are assumed to lie in a surface layerwith a height varying with time. • A reanalysis data set is tested to show the efficiency of ASoRA in its global mode. • The estimated annual average of the solar resource parameters is given for Ouarzazate in 2014. The ASoRA method consists in estimating the solar resource in tower concentrated solar plants by exploiting global data sets. The solar resource parameters are not only the Direct Normal Irradiance (DNI) but also the slant path transmittance (T sp). The column to surface-level conversion process was validated by comparing the retrieved aerosol extinction coefficient (AEC) to independent measurements performed by a ground-based nephelometer. The Aerosol Robotic NETwork (AERONET) provided column-integrated aerosol extinction properties. The European Centre for Medium-Range Weather Forecasts Reanalysis Interim boundary layer height was used to reproduce the seasonal dependence of the aerosol vertical profile. At the daily resolution, ASoRA reproduced observed AEC with a relative root mean square difference (rRMSD) of 33% and a correlation coefficient of 0.90. The spectral extrapolation from monochromatic measurements to the solar broadband was validated by comparing computations and observations of DNI. ASoRA was also able to reproduce the hourly variability of DNI observed by a pyrheliometer with a RMSD of 38 W/m2, a rRMSD of 4.6%, and a correlation coefficient larger than 0.98. Despite larger uncertainties caused by using Modern-Era Retrospective analysis for Research and Applications (version 2) instead of AERONET, the annual average of T sp was underestimated by only 0.01, and the annual average of the irradiance loss in the slant path by only 4 W/m2. Largest impact on T sp comes from the parameterisation of the aerosol vertical profile, and the annual average of T sp was 0.945 at Ouarzazate (Morocco) in 2014, with an estimated uncertainty of 0.030. [ABSTRACT FROM AUTHOR]

Brahmaputra Valley of northeast India is relatively pristine, with low local emission levels, but is susceptible to long-range transport from west Asian deserts. Hourly measurements of aerosol particulate matter (PM2.5 and PM10) and black carbon (BC) over a period of 1 year (June 2013–May 2014) over Tezpur station (26.63° N, 92.77° E), located in the Brahmaputra Valley, display annual mean PM2.5 and BC of 42 ± 25 µg m−3 and 6 ± 1.5 µg m−3, respectively, indicating that Tezpur enjoys lower pollution levels than other northeast stations. The lowest concentrations of PM2.5 and PM10 (~ 14.7 and 24 µg m−3, respectively) are observed during the monsoon season (JJAS). The highest values (~ 91 and 114 µg m−3) are observed during the winter (DJF) due to local atmospheric conditions and some additional transport from the west Asian deserts and the Indo-Gangetic Basin (IGB). Local emissions seem to be mainly responsible for moderate values (~ 24 and 42 µg m−3) of PM during the post-monsoon (ON) season with weak winds. Coarse particles (diameter > 2.5 µm) are much higher (approx. 47% of PM10) in the pre-monsoon than in the other seasons due to the long-range transport of dust particles from the IGB and west Asian deserts as well as sea salt particles from the Bay of Bengal. WRF-Chem model simulation underestimated the concentration of PM2.5 and PM10 as compared to daily mean observations. The variation in the "model–observation" time series for relative humidity (RH) and boundary layer height suggests that underestimation of PM10 is due mainly to the underestimation of RH and overestimation of the ventilation coefficient by the model during winter and pre-monsoon seasons. [ABSTRACT FROM AUTHOR]

Abstract We report the variability of Boundary Layer Height (BLH) and Ventilation Coefficient (VC) over a coastal station in southwest Peninsular India from vertical soundings. Altitude profile of Virtual Potential Temperature (θ v) (derived from balloon-borne GPS radiosonde observations) was used to study the seasonal changes of BLH over Thumba (8.5°N, 77°E), a coastal station in southwest Peninsular India. Variability in the BLH is maximum during the pre-monsoon season and minimum during the winter, whereas the VC was found to be highest in the summer and lowest during winter. It is revealing the excellent efficiency in the dispersion of pollutants during the summer monsoon season. Conversely, low VC during winter and post-monsoon seasons showed great potential for pollution at this site. Role of VC on the dispersion of pollution was also examined using surface mass concentration of Black and Organic Carbon (BC and OC), sulphate and columnar Aerosol Optical Depth (AOD). High value of VC lowers the surface mass concentrations of BC, OC and sulphate during winter and maximises during summer monsoon and decreases the pollution potential. Highlights • Location of the station is on the SW coast of India where monsoon makes its onset. • At this station the wind direction reverses from winter to summer. • BLH and VC have been studied using Pisharoty Sonde, MERRA reanalysis and MODIS data. • BLH/VC variability and its role on pollutant dispersion were presented in detail. • Seasonal variability of pollutant dispersion has been analyzed. [ABSTRACT FROM AUTHOR]

The planetary boundary layer (PBL), which directly interacts with the underlying surface, differs significantly in its nature from the low-turbulent stably stratified free atmosphere. Fluctuations of the Earth's surface heat balance immediately affect the PBL and assimilate there owing to the effective mechanism of turbulent heat transfer. In this case the upper boundary of the PBL plays the role of a cover, preventing the direct penetration of thermal effects and contaminants into an overlying atmospheric layer. In view of this, air pollution is especially dangerous when associated with shallow PBL. In addition, local peculiarities of climate change are mainly determined by the PBL height due to the high sensitivity of thin stably stratified PBLs to the thermal effects. Deep convective PBLs are not very sensitive to weak thermal effects, but they significantly affect the formation of convective cloudiness and the climate system as a whole by means of the turbulent entrainment of the thermal energy, humidity, aerosols, and other admixtures through the upper boundary. The PBL height and turbulent entrainment must be calculated when simulating and forecasting air pollution, abnormal frosts and heat, and other hazardous phenomena. In this paper we discuss the state-of-the-art knowledge in the area of PBL height simulation and suggest a new model of turbulent entrainment for convective PBLs. [ABSTRACT FROM AUTHOR]

Abstract: This study used sunphotometer, lidar, and surface particulate matter measurements to assess MODIS AOD products for air quality monitoring in Taiwan. The MODIS AOD retrievals revealed a satisfactory validation against AERONET measurements with correlation coefficient ∼0.91 during Terra and ∼0.83 during Aqua overpasses in the period of 2006–2008. The correlations in cold season (September–February) ∼0.85–0.96 appear to be slightly higher than those in warm season (March–August) ∼0.78–0.87. The relationships derived between PM2.5 and AOD from both MODIS and AEROENT show a strong seasonality as a result of aerosol vertical distribution. The high correlations (∼0.88–0.93) obtained in autumn between PM2.5 and AOD normalized by boundary layer height (or equivalent haze layer height) are attributed to stable and well-mixed boundary layers as opposed to the summer lows (∼0.12–0.67) resulted from strong convection associated with unstable weather systems. With the long-range transport of Asian dust and pollution in winter and spring under prevalent northeasterly and biomass burning from Southeast Asia in spring under prevalent southwesterly flows, better correlation is derived from the normalization by haze layer height than boundary layer height owing to abundance of aerosols aloft above boundary layer. The former is shown with correlation coefficients in the range of ∼0.76–0.87 and ∼0.77–0.80 and the latter ∼0.56–0.79 and ∼0.39–0.54 for winter and spring, respectively. The results of MODIS that uphold the relationships derived from AERONET in autumn, winter, and spring suggest MODIS AOD products have the level of quality as sunphotometer measurements for monitoring local PM2.5 in Taiwan. [Copyright &y& Elsevier]

The turbulent mixing and dispersion of air pollutants is strongly dependent on the vertical structure of the wind, which constitutes one of the major challenges affecting the determination of boundary layer height (BLH). Here, an adaptive method is proposed to estimate BLH from measurements of radar wind profilers (RWPs) in Beijing (BJ), Nanjing (NJ), Chongqing (CQ), and Wulumuqi (WQ), China, during the summer of 2019. Validation against simultaneous BLH estimates from radiosondes (RSs) yielded a correlation coefficient of 0.66, indicating that the method can be used to derive BLH from RWPs. Diurnal variations of BLH and the ventilation coefficient (VC) at four sites were then examined. A distinct diurnal cycle of BLH was observed over all four cities; BLH gradually increased from sunset, reached a maximum in the afternoon, and then dropped sharply after sunset. The maximum hourly average BLH (1.426 ± 0.46 km) occurred in WQ, consistent with the maximum hourly mean VC larger than 5000 m2/s observed there. By comparison, the diurnal variation of VC was not strong, with values ranging between 2000 and 3000 m2/s, likely owing to the high-humidity environment. Furthermore, surface sensible heat flux, latent heat flux, and dry mass of particulate matter with aerodynamic diameter ≤2.5 µm (PM2.5) concentrations were found to somehow affect the vertical structure of wind and thermodynamic features, leading to a difference between RS and RWP BLH estimates. This indicates that the atmospheric environment can affect BLH estimates using RWP data. The BLH results from RWPs were better in some specific cases. These findings show great potential of RWP measurements in air quality research, and will provide key data references for policy-making toward emission reductions. [ABSTRACT FROM AUTHOR]