RESUMEN

With the rapidly changing aerosol emissions due to the increase in urbanization, energy consumption, population density, and industrialization in the past two decades across the globe, there is an evolution of different chemical properties of aerosols that are yet not quantified properly. Therefore, a rigorous attempt is made in this study to obtain the long-term changing patterns in the contribution of different aerosol types/species, to the total aerosol loading. This study is carried out only over those regions exhibiting either increasing or decreasing trends in the aerosol optical depth (AOD) parameter on a global scale. Applying the multivariate linear regression trend analysis on Modern-Era Retrospective Analysis for Research and Application version 2 (MERRA-2) aerosol species dataset obtained between 2001 and 2020, we found that despite the overall statistically significant decrease in total columnar AOD trend values over North-Eastern America, and Eastern and Central China regions, an increase in the dust and organic carbon aerosols is observed, respectively. As the uneven vertical distribution of aerosols can alter the direct radiative effects, the extinction profiles of different aerosol types obtained using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) dataset between 2006 and 2020, are further partitioned, for the first time, based on their presence in different altitudes (i.e., within the atmospheric boundary layer and free-troposphere) as well as measurement timing (i.e., daytime and night-time) regimes. The detailed analysis showed that there exists an overall higher contribution of aerosols persisting in the free troposphere region which in turn can have a long-term effect on climate due to their higher residence time, particularly absorbing aerosols. As the trends are mostly associated with the changes in energy use, regional regulatory policies, and/or changing background meteorology conditions, therefore this study also elaborates on the effectiveness of these factors with the changes obtained in different aerosol species/types over the region.

RESUMEN

Phase-wise variations in different aerosol (BC, AOD, PM1, PM2.5 and PM10), radiation (direct and diffused) and trace gases (NO, NO2, CO, O3, SO2, CO2 and CH4) and their associated chemistry during the COVID-19 lockdown have been investigated over a tropical rural site Gadanki (13.5° N, 79.2° E), India. Unlike most of the other reported studies on COVID-19 lockdown, this study provides variations over a unique tropical rural environment located at a scientifically strategic location in the Southern Indian peninsula. Striking differences in the time series and diurnal variability have been observed in different phases of the lockdown. The levels of most species that are primarily emitted from anthropogenic activities reduced significantly during the lockdown which also impacted the levels and diurnal variability of secondary species like O3. When compared with the same periods in 2019, short-lived trace gas species such as NO, NO2, SO2 which have direct anthropogenic emission influence have shown the reduction over 50%, whereas species like CO and O3 which have direct as well as indirect impacts of anthropogenic emissions have shown reductions up to 10%. Long-lived species (CO2 and CH4) have shown negligible difference (<1%). BC and AOD have shown reductions over 20%. Particulate Matter (1, 2.5 and 10) reductions have been in the range of 40 to 50% when compared to the pre-lockdown period. The changes in shortwave downward radiation at the surface, diffuse component due to the scattering and diffuse fraction have been +2.2%, -4.1% and -2.4%, respectively, in comparison with 2019. In contrast with the studies over urban environments, air quality category over the rural environment remained same during the lockdown despite reduction in pollutants level. All the variations observed for different species and their associated chemistry provides an excellent demonstration of rural atmospheric chemistry and its intrinsic links with the precursor concentrations and dynamics.

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RESUMEN

Analysis of the climatology of aerosol properties is performed over Hanle (4500 m) and Merak (4310 m), two remote-background sites in the western trans-Himalayas, based on eleven years (2008-2018) of sun/sky radiometer (POM-01, Prede) measurements. The two sites present very similar atmospheric conditions and aerosol properties allowing us to examine them as continuous single-data series. The annual average aerosol optical depth at 500 nm (AOD500) is 0.04 ± 0.03, associated with an Ångström exponent (AE440-870) of 0.58 ± 0.35 and a single scattering albedo (SSA500) of 0.95 ± 0.05. AOD500 exhibits higher values in May (~0.07) and lower in winter (~0.03), while AE400-870 minimizes in spring, indicating influence by coarse-mode dust aerosols, either emitted regionally or long-range transported. The de-convolution of AOD500 into fine and coarse modes justifies the aerosol seasonality and sources, while the marginal diurnal variation in all aerosol properties reveals a weak influence from local sources, except for some few aerosol episodes. The aerosol-volume size distribution presents a mode value at ~10 µm with secondary peaks at accumulation (~ 2 µm) and fine modes (~0.03 µm) and low variability between the seasons. A classification of the aerosol types based on the fine-mode fraction (FMF) vs. SSA500 relationship reveals the dominance of aerosols in the FMF range of 0.4-0.6, characterized as mixed (39%), followed by fine aerosols with high scattering efficiency (26%), while particles related to dust contribute ~21%, with low fractions of fine-absorbing aerosols (~13%). The aerosol radiative forcing (ARF) estimates reveal a small cooling effect at the top of the atmosphere (-1.3 Wm-2), while at the surface, the ARF ranges from -2 Wm-2 to -6 Wm-2 on monthly basis. The monthly-mean atmospheric radiative forcing (~1 to 4 Wm-2) leads to heating rates of 0.04 to 0.13 K day-1. These ARF values are higher than the global averages and may cause climate implications over the trans-Himalayan region.

RESUMEN

Efforts to understand the chemical composition of Asian Tropopause Aerosol Layer (ATAL) in the Upper Troposphere Lower Stratosphere (UTLS) region have revealed the dominance of nitrates in the samples collected from ATAL layer during the recent balloon campaigns. Potential sources have been thought to be in-situ formation, convective uplift and long-range transport. Rainwater chemical composition consists water-soluble chemical ions that are wet scavenged during rain events and gives an indirect indication of lower atmospheric pollutants. Keeping this in focus, total monsoon precipitation chemistry at Gadanki (13.5°N, 79.2°E) has been studied to understand the convective uplift possibilities to the UTLS region. About 32 rainwater samples collected during July to December 2017 were analysed for their chemical composition using Ion Chromatography. Total 16 ions comprising of 5 anions (F-, Cl-, NO3-, SO42- and PO43-), 6 cations (Na+, K+, Ca2+, Mg2+, Li+ and NH4+) and 5 trace metals (Cd2+, Ni2+, Co2+, Mn2+ and Zn2+) have been detected in different rainwater samples. Rainwater chemical composition data has been subjected to the Principal Component Analysis (PCA) to understand the correlations between different chemical species and to identify the possible sources of origin qualitatively. It has been observed that the chemical composition of the rainwater is very different from the chemical composition of the ATAL layer indicating non-existence of convective transport of lower level pollutants to the UTLS region at Gadanki. This observation is also well supported by the vertical distribution of CALIPSO derived aerosol types and ERA interim vertical pressure velocities during the sampling period.

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