The present study summarizes two decades (2000–2019) of climatology and trends in aerosol loading and optical properties using a high spatial resolution data obtained from NASA's MODIS MAIAC and MISR ...aerosol products supplemented by moderate resolution aerosol data from OMI sensor over South Asia (SA). MISR AOD showed good agreement against AERONET AOD with 68.68% of the retrievals falling within the expected error and high Pearson's correlation coefficient (R = 0.83). The 20 years geometric mean of MAIAC and MISR AOD revealed higher loading of aerosols over the Indo-Gangetic Plain (IGP) and Eastern coast of India by 30% to 44% compared to the mean AOD over the entire SA. The highest mean AOD under cloud-free conditions was noted during monsoon season, followed by pre-monsoon, post-monsoon, and winter. The high contribution of coarse-mode AOD (cAOD) mainly from natural aerosol emission and small-mode AOD (sAOD) from local anthropogenic emissions are the main driver to high AOD in monsoon and pre-monsoon seasons. Besides, the presence of high humidity during the monsoon season favors the hygroscopic growth of the particles and leads to higher AOD values over SA. The high spatial resolutions of MODIS/MAIAC and MISR aerosol products enabled the identification of previously unobserved aerosol hotspots over Bihar, West Bengal, and the eastern Indian coastal state of Odisha, which is mainly dominated by small aerosol particles. The contributions of smaller aerosol particles to the total aerosol loading were found to be higher during post-monsoon and winter over most states in India, Nepal, and Bangladesh. In contrast, the contribution of coarser particles was higher over Pakistan during pre-monsoon and monsoon seasons. Smaller particles were predominantly retrieved over the Indian states dominated by mining industries, including Jharkhand and Odisha. A typical dominance of absorbing carbonaceous aerosols was also noted over the northwestern region of IGP during post-monsoon, which otherwise was mainly affected by mixed dust aerosols and carbonaceous aerosols in pre-monsoon and monsoon seasons. A statistically significant positive temporal trend in AOD was observed for the whole study period, over most of the SA region, which was influenced by the increase in small particles over India and Bangladesh. Urban/industrial weakly absorbing aerosols were found to be the main contributor to a similarly positive trend over Central India and East coast Indian states. Overall, recent advancements in high spatial resolution satellite-based aerosol optical properties showed good potential to identify the aerosol hotspots and constrain aerosol types across a highly polluted SA region.
•The latest MISR V23 AOD product showed promising agreement with ground observations.•Significant positive trends in MISR and MAIAC AOD are identified over South Asia.•Climatological trends recognize the Eastern Indian coast as a new aerosol hotspot.•Small aerosol particles contribute to >54% of the total AOD in all seasons.•Anthropogenic sources are the major contributor to high aerosol loading over SA.
For atmospheric sulfuric acid (SA) concentrations the presence of dimethylamine (DMA) at mixing ratios of several parts per trillion by volume can explain observed boundary layer new particle ...formation rates. However, the concentration and molecular composition of the neutral (uncharged) clusters have not been reported so far due to the lack of suitable instrumentation. Here we report on experiments from the Cosmics Leaving Outdoor Droplets chamber at the European Organization for Nuclear Research revealing the formation of neutral particles containing up to 14 SA and 16 DMA molecules, corresponding to a mobility diameter of about 2 nm, under atmospherically relevant conditions. These measurements bridge the gap between the molecular and particle perspectives of nucleation, revealing the fundamental processes involved in particle formation and growth. The neutral clusters are found to form at or close to the kinetic limit where particle formation is limited only by the collision rate of SA molecules. Even though the neutral particles are stable against evaporation from the SA dimer onward, the formation rates of particles at 1.7-nm size, which contain about 10 SA molecules, are up to 4 orders of magnitude smaller compared with those of the dimer due to coagulation and wall loss of particles before they reach 1.7 nm in diameter. This demonstrates that neither the atmospheric particle formation rate nor its dependence on SA can simply be interpreted in terms of cluster evaporation or the molecular composition of a critical nucleus.
Significance A significant fraction of atmospheric aerosols is formed from the condensation of low-volatility vapors. These newly formed particles can grow, become seeds for cloud particles, and influence climate. New particle formation in the planetary boundary layer generally proceeds via the neutral channel. However, unambiguous identification of neutral nucleating clusters has so far not been possible under atmospherically relevant conditions. We explored the system of sulfuric acid, water, and dimethylamine in a well-controlled laboratory experiment and measured the time-resolved concentrations of neutral clusters. Clusters containing up to 14 sulfuric acid and 16 dimethylamine molecules were observed. Our results demonstrate that a cluster containing as few as two sulfuric acid and one or two dimethylamine molecules is already stable against evaporation.
A lightweight unmanned aerial vehicle (UAV) was outfitted with miniaturized sensors to investigate the vertical distribution patterns and sources of fine aerosol particles (PM2.5) within the 1 000 m ...lower troposphere. A total of 16 UAV flights were conducted in the Yangtze River Delta (YRD) region, China, from the summer to winter in 2014. The associated ground-level measurements from two environmental monitoring stations were also used for background analysis. The results show that ground-level PM2.5 concentrations demonstrated a decreasing trend from Feb. to Jul. and an increasing trend from Aug. to Jan. (the following year). Higher PM2.5 concentrations during the day were mainly observed in the morning (Local Time, LT 05-09) in the spring and summer. However, higher PM2.5 concentrations occurred mainly in the late afternoon and evening (LT 16-20) in the autumn and winter, excluding severe haze pollution days when higher PM2.5 concentrations were also observed during the morning periods. Lower tropospheric PM2.5 concentrations exhibited similar diurnal vertical distribution patterns from the summer to winter. The PM2.5 concentrations decreased with height in the morning, with significantly large vertical gradients from the summer to winter. By contrast, the aerosol particles were well mixed with PM2.5 concentrations of lower than 35 μg⋅m−3 in the early afternoon (LT 12-16) due to sufficient expansions of the planetary boundary layer. The mean vertical PM2.5 concentrations within the 1 000 m lower troposphere in the morning were much larger in the winter (∼87.5 μg⋅m−3) than in the summer and autumn (∼20 μg⋅m−3). However, subtle differences of ∼11 μg⋅m−3 in the mean vertical PM2.5 concentrations were observed in the early afternoon from the summer to winter. The vertical distribution patterns of black carbon and its relationships with PM2.5 indicated that the lower tropospheric aerosol particles might be mainly derived from fossil-fuel combustion sources. In addition, a 48-h backward trajectory analysis of air parcels showed that the lower tropospheric aerosol particles were mainly from emissions of local sources in the YRD region in the summer and autumn. By sharp contrast, the aerosol particles of this region in the winter were mainly of long-range transport sources from the north and northwest China due to the impact of Asian winter monsoon.
•The lightweight UAV platform is relatively reliable.•Vertical distribution patterns of PM2.5 are similar in different seasons.•Lower tropospheric PM2.5 in the afternoon increase slightly in the winter.•Aerosol particles of the YRD originate from different regions in different seasons.
Biological aerosols play an important role in atmospheric chemistry, clouds, climate, and public health. Here, we studied the morphology and composition of primary biological aerosol particles ...(PBAPs) collected in the Lesser Khingan Mountain boreal forest of China in summertime using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). C, N, O, P, K, and Si were detected in most of the PBAPs, and P represented a major marker to discriminate the PBAPs. Of all detected particles >100 nm in diameter, 13% by number were identified as PBAPs. We found that one type of PBAPs mostly appeared as similar rod-like shapes with an aspect ratio > 1.5. Size distribution of the rod-like PBAPs displays two typical peaks at 1.4 μm and 3.5 μm, which likely are bacteria and fungal particles. The second most PBAPs were identified as fungal spores with ovoid, sub-globular or elongated shapes with a smooth surface and small protuberances with their dominant size range of 2–5 μm. Moreover, we found some large brochosomal clusters containing hundreds of brochosomes with a size range of 200–700 nm and a shape like a truncated icosahedron. We estimated that mass concentration of PBAPs approximately 1.9 μg m−3 and contributed 47% of the in situ PM2.5–10 mass. The detection frequency and concentration of PBAPs were higher at night than in the daytime, suggesting that the relative humidity dramatically enhanced the PBAPs emissions in the boreal forest. Our study also showed that the fresh PBAPs displayed weak hygroscopicity with a growth factor of ~1.09 at RH = 94%. TEM analysis revealed that about 20% of the rod-like PBAPs were internally mixed with metal, mineral dust, and inorganic salts in the boreal forest air. This work for the first time provides the overview of individual PBAPs from nanoscale to microscale in Chinese boreal forest air.
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•Morphology, composition, and size of PBAPs were observed by electron microscope.•Rod-like PBAPs (e.g., bacteria, fungi), fungal spores, and brochosomes were found.•PBAPs tend to emit at night under high humidity rather than in the daytime.
To investigate the interannual evolution of air pollution in summer and the impact of the COVID-19 lockdown on local pollution in Chengdu, China, single aerosol particles were continuously measured ...in three summer periods: the regular period in 2020 (RP2020); the regular period in 2022 (RP2022); and the lockdown period in 2022 (LP2022). It was found that, from RP2020 to RP2022, the mass concentrations of PM2.5, PM10, SO2 and NO2 decreased by 25.6 %, 24.7 %, 28.8 % and 38.5 %, respectively, while the concentration of O3 increased by 11.0 %. Affected by regional transport, there was no significant decrease in the concentrations of various pollutants during LP2022. All single aerosol particles could be classified into seven categories: vehicle emissions (VE), dust, biomass burning (BB), coal combustion (CC), K mixed with sulfate (KSO4), K mixed with nitrate (KNO3) and K mixed with sulfate and nitrate (KSN) particles. From RP2020 to RP2022, the contributions of BB and CC particles decreased by 12.1 % and 0.9 %, respectively, while VE and dust particles increased by 3.6 % and 2.5 %, respectively; and compared to RP2022, the contributions of VE, dust and CC particles in LP2022 decreased by 22.2 %, 11.0 % and 12.7 %, respectively. The high PM2.5 pollution events in RP2020 and RP2022 were mainly caused by combustion sources (BB and CC, 51.6 %) and VE (38.3 %) particles, respectively, while the pollution event in LP2022 was contributed by BB (27.0 %) and secondary inorganic (KSO4, KNO3 and KSN, 60.2 %) particles. The formation mechanisms of different pollution events were further validated by WRF-Chem results. Although the potential source areas of particles showed a shrinking trend from RP2020 to RP2022, regional transport still caused high PM2.5 pollution events during LP2022. Photochemical processes dominated the formation of KSO4 particles, while the KNO3 and KSN particles were mainly generated by liquid-phase reactions, and this effect increased year by year.
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•Surface components of particles during a haze episode are analyzed by TOF-SIMS.•Complex inorganic and organic species are detected on sample surface.•TOF-SIMS chemical mapping and ...SEM imaging facilitate individual particle analysis.•Source apportionment is conducted by TOF-SIMS mass spectra combined with PCA.
The atmospheric aerosol particles have a potential heavy burden on environment, climate, and human health, which were closely related to the surface physicochemical properties. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) technique is a powerful tool to obtain detailed surface chemical information since it has high surface sensitivity for both elements and molecular ions, and high mass resolution. In this work, size-fractioned aerosol particles in the range of 0.43–10 µm during a severe haze episode in Beijing were analyzed by TOF-SIMS, the variation characteristics of chemical species corresponding to particle size and air pollution level was investigated by the normalization of secondary ion intensities, the possible sources were identified through principal component analysis (PCA), and the influence of meteorological factors and air mass transmission were also investigated. The study results showed that the surface chemical components of PM2.5 were more complicated during haze episode than on clean days. A total of 17 organic and inorganic species were detected, including crustal elements, heavy metals, sulfate, nitrate, siliceous compounds, hydrocarbons, oxygen-containing organics, and nitrogen-containing organics. In general, the particle surface mainly contained crustal elements, hydrocarbons, and carbon-containing inorganics. Organic and secondary ions significantly increased in heavy-polluted days, indicating the aging process of particles. Inorganic compounds had a higher percentage in coarse mode, while organic compounds were higher in accumulation mode. PCA results indicated that urban aerosol during this haze episode mainly came from vehicle emissions (24.7%), coal-fired combustion (22.4%), organic aerosol (19.3%), and dust resuspension (19.6%). The northern air mass could facilitate the dilution of air pollutants with the surface secondary formed components of particles significantly decreased.
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