Aerosols heat up the Himalayan climate

Seasonal variation of particle number concentration in a busy urban street with exposure assessment and deposition in human respiratory tract

Ultrafine particles (UFP) associated with air quality and health impacts are a major concern in growing urban regions. Concentrations of UFP (particles of size between 10 and 100 nm) and accumulation mode (Nacc) (particles of size >100 and up to 1000 nm), are analyzed over a highly polluted megacity, Delhi, in conjunction with vehicular flow density, during peak (morning, and evening) and non-peak hours. UFP contributes ≥60% to total particle concentration during autumn and monsoon. UFP concentrations are about 50,000 particles per cm3 in winter which reduces to about 25,000 particles during monsoon. Nacc are about 20,000 (winter) and 10,000 (monsoon) particles per cm3. UFP concentration and Nacc during peak hours are at least twice higher than those obtained in non-peak hours, confirming the dominant influence of emissions from vehicular exhaust in the study region. Seasonal analysis of UFP size distribution reveals that direct emissions dominate the particle concentrations during winter and autumn, whereas new particle formation mechanism contributes the highest in spring and summer. Assessment of inhalable particle number concentration and particle deposition in the human respiratory tract using Multiple Path Particle Dosimetry (MPPD) model, performed for the first time, shows that the order in which these particles deposit in the human respiratory tract is alveoli > bronchiole > bronchus. The deposition ranges between 10 and 18 million nanoparticles during different hours of the day, whereas the estimated inhalable particle concentration (IPN) varies between 0.5 and 1 billion. Results on the IPN during activities classified from light (walking), medium, heavy, very heavy to severe (long-distance running) provide insights into health effects on vulnerable populations. These quantitative results obtained over a megacity on hourly and seasonal variations of nanoparticles along with IPN and deposition rates for different activities are important, and are invaluable inputs for developing mitigation policies aimed to improve air quality and public health, both of which are major concerns in South Asia.

Unveiling global land fine- and coarse-mode aerosol dynamics from 2005 to 2020 using enhanced satellite-based monthly inversion data

Accurate fine-mode and coarse-mode aerosol knowledge is crucial for understanding their impacts on the climate and Earth's ecosystems. However, current satellite-based Fine-Mode Aerosol Optical Depth (FAOD) and Coarse-Mode Aerosol Optical Depth (CAOD) methods have drawbacks including inaccuracies, low spatial coverage, and limited temporal duration. To overcome these issues, we developed new global-scale FAOD and CAOD from 2005 to 2020 using a novel deep learning model capable of the synergistic retrieval of two aerosol sizes. After validation with the aerosol robotic network (AERONET) and sky radiometer network (SKYNET), the new monthly FAOD and CAOD showed significant improvements in accuracy and spatial coverage. From 2005 to 2020, the new data showed that China had the greatest decrease in FAOD and CAOD. In contrast, India and South Latin America had a significant increase in FAOD versus North Africa in CAOD. FAOD in the regions of Argentina, Paraguay, and Uruguay in South America have shown an upward trend. The results reveal that FAOD and CAOD display distinct patterns of change in the same regions, particularly on the west coast of the United States where FAOD is increasing, while CAOD is decreasing. Aside from the year 2020 due to the global COVID-19 pandemic, the analysis showed that although China has seen at least an +85% increase in energy consumption and urban expansion in 2019 compared to 2005 due to the needs of development and construction, the implementation of China's air pollution control policies has led to a significant decrease in FAOD (-46%) and CAOD (-65%) after 2013. This research enriches our comprehension of global fine and coarse aerosol patterns, additional investigations are needed to determine the potential global implications of these changes.

Implications of equivalent black carbon heterogeneity in south Indian high-altitude eco-sensitive region

Large-scale representative source apportionment studies are uncommon, undermining source contribution studies in India, particularly in high-altitude locations. Kodaikanal is a high-altitude region in India's Western Ghats, with spatial heterogeneity of sources altering chemical complexity; thus, the associated implications are unknown. We conducted the campaign study REBER (Research on Equivalent Black Carbon Monitoring in an Eco-sensitive Region) at three Kodaikanal sites to understand local point sources, characteristics, and distribution of eBC during the winter-to-summer monsoon transition. For two main reasons: to understand the seasonal change of BC since the transition period has the lowest wind speeds and the highest particulate concentrations and is prone to high pollution events most often during seasonal transition months, and to study local pollution since the meridional monsoon and zonal winds in study region weaken whereby the transport of pollutants from ocean to land and vice versa is minimal. The results showed that the eBC mass concentration was 85% higher than in the previous study conducted by Bhaskar et al. (2018) during the monsoon transition period. To determine the ratio of fossil fuel and wood-burning sources, a real-time apportionment model of atmospheric eBC is used. The percentage of wood burning in the background location ranges from 21.12 to 88.98%. Wood burning leads in residential sites with 57.5 ± 7.3%, whereas fossil fuel contribution dominates traffic sites with 69.84 ± 10.2%. Fossil fuel contributions are significant in different characteristics of environments, ranging from 42.5 to 69.84%. The results of the conditional bivariate probability function (CBPF) analysis pointed out a competition between anthropogenic and natural sources to contribute as local sources to the monitoring stations. A scanning electron microscope (SEM) paired with an energy dispersive X-ray (EDX) analysis found that the particle size was 93% relatively large compared to other hill stations in India. The variation in the chemical constituents indicates that the particles originated from various sources.