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Delhi, a tropical Indian megacity, experiences one of the most severe air pollution in the world, linked with diverse anthropogenic and biomass burning emissions. First phase of COVID-19 lockdown in India, implemented during 25 March to 14 April 2020 resulted in a dramatic near-zeroing of various activities (e.g. traffic, industries, constructions), except the "essential services". Here, we analysed variations in the fine particulate matter (PM 2.5 ) over the Delhi-National Capital Region. Measurements revealed large reductions (by 40-70%) in PM 2.5 during the first week of lockdown (25-31 March 2020) as compared to the pre-lockdown conditions. However, O 3 pollution remained high during the lockdown due to non-linear chemistry and dynamics under low aerosol loading. Notably, events of enhanced PM 2.5 levels (300-400 µg m -3 ) were observed during night and early morning hours in the first week of April after air temperatures fell close to the dew-point (~ 15-17 °C). A haze formation mechanism is suggested through uplifting of fine particles, which is reinforced by condensation of moisture following the sunrise. The study highlights a highly complex interplay between the baseline pollution and meteorology leading to counter intuitive enhancements in pollution, besides an overall improvement in air quality during the COVID-19 lockdown in this part of the world.

The spatial–temporal variations of fine particulate matter (PM2.5) in Akure, a city in southwestern Nigeria, are examined based on multi-year continuous observations using low-cost PM2.5 sensors at six different sites. The average annual concentration of PM2.5 across these sites was measured at 41.0 µg/m3, which surpassed both the Nigerian national air quality standard and the World Health Organization air quality guideline level. PM2.5 levels were significantly higher during the dry season (November–March), often exceeding hazardous levels (over 350 µg/m3), than during the wet season. The analyses of trends in air mass trajectories and satellite data on fire occurrences imply that the transport of dust and accumulation of PM2.5 originating from local/regional open burning activities played crucial roles in increased PM2.5 concentrations during the dry season. Further, site-to-site variations in the PM2.5 levels were observed, with relatively high concentrations at less urbanized sites, likely due to high local emissions from solid fuel combustion, waste burning, and unpaved road dust. Diurnal patterns showed morning and evening peaks at less urbanized sites, accounting for an estimated 51–77% of local emissions. These results highlight the importance of local emission sources in driving spatial–temporal PM2.5 variations within the city and the need for targeted mitigation strategies to address the significant air pollution challenges in Akure and similar regional cities in West Africa. [ABSTRACT FROM AUTHOR]

A horizontally pointing lidar is planned for deployment with other instruments in Fukushima, Japan, to continuously monitor and characterize the optical properties of radioactive aerosols and dust in an uninhabited area. Prior to installation, the performance of the lidar is tested at Chiba University. Data from the continuous operation of the lidar from August 2021 to February 2022 are analyzed for extinction and volume linear depolarization ratio. These are compared with the weather sensor and particulate matter (PM 2.5) measurements to quantify the relationships between atmospheric conditions and optical properties of near-ground aerosols. The results show that the lidar data's extinction coefficient and depolarization ratio can have a quantifiable relationship with relative humidity (RH), absolute humidity, rain rate, wind speed, wind direction and PM 2.5 concentration. Analysis of the 7-month data shows that the optical properties of aerosol and dust depend on the combined effects of the weather parameters. An increase in RH or PM 2.5 concentration does not imply an increase in radioactive aerosols. The average extinction coefficient and depolarization ratio of aerosols and dust, originating from the land and ocean, show different values and opposing trends, which can aid in determining the occurrence of ground-based radioactive dust and aerosols. The information obtained from analyzing the inter-relationship among lidar, weather parameters and PM 2.5 concentration is essential in assessing the occurrence of radioactive aerosols and characterizing local aerosol–weather relationships in a radioactive area. This result provides essential information in describing radioactive aerosols in Fukushima. [ABSTRACT FROM AUTHOR]

A horizontally pointing lidar is planned for deployment with other instruments in Fukushima, Japan, to continuously monitor and characterize the optical properties of radioactive aerosols and dust in an uninhabited area. Prior to installation, the performance of the lidar is tested at Chiba University. Data from the continuous operation of the lidar from August 2021 to February 2022 are analyzed for extinction and depolarization ratio. These are compared with the weather sensor and particulate matter (PM2.5) measurements to quantify the relationship between atmospheric conditions and optical properties of near-ground aerosols. The results show that lidar data's extinction coefficient and depolarization ratio can have a quantifiable relationship with relative humidity (RH), absolute humidity, rain rate, wind speed, wind direction, and PM2.5 concentration. Analysis of the seven-month data shows that the optical properties of aerosol and dust depend on the combined effects of the weather parameters. An increase in RH or PM2.5 concentration does not imply an increase in radioactive aerosols. The average extinction coefficient and depolarization ratio of aerosols and dust originating from the land and ocean show different values and opposing trends which can aid in determining the occurrence of ground-based radioactive dust and aerosols. The information obtained from analyzing the interrelationship among lidar, weather parameters, and PM2.5 concentration is essential in assessing the occurrence of radioactive aerosols and characterizing local aerosol-weather relationships in a radioactive area. This result provides essential information in describing radioactive aerosols in Fukushima. [ABSTRACT FROM AUTHOR]

The genesis, dynamics, and impacts of a severe dust storm over the central Himalaya during June 13–17, 2018 have been investigated using in situ measurements, satellite data, and model reanalysis. A low‐pressure system over northern India and prevalence of strong winds (∼20 ms−1) triggered the dust storm leading to poor visibility conditions and five‐fold enhancement in the fine particulate matter (PM2.5) over the central Himalaya. Enhancements in Aerosol Optical Depth (AOD) were observed to be stronger over the Himalayan foothills site (Lumbini) than that over the Indo‐Gangetic Plain (IGP) site‐Gandhi College. The sharp reductions in Angstrom exponent (α) from about 1.2 to 0.3 indicated the dominance of coarse‐mode aerosols during the dust episode. Model results show an enhancement in the dust from 1.5 to 2.5 Tg (∼70%) over the northern Indian subcontinent, with about half of the contribution from the regional source (Thar Desert). Interestingly, dust storm also had significant impacts on turbulent kinetic energy (2.9–9.6 m2 s−2), vertical momentum flux (0.9–3.3 Nm−2), and sensible heat flux (34.8 to −33.9 Wm−2), suggesting turbulent mixing of aerosols and cooling near the surface over the Himalayas. Our study highlights that the large‐scale dust storms exposed to additional dust and pollution from regional sources can profoundly impact the air quality, heat fluxes, and radiative balance over the northern Indian subcontinent. The study would also help in evaluating the results of climate models and to assess the impacts of dust on the hydrological processes and melting Himalayan glaciers. Key Points: A detailed investigation on the genesis, dynamics, and impacts of a severe dust storm over northern Indian subcontinent has been conductedAnalysis on the relative effects of long‐range transport and regional dust emissions affecting northern Indian subcontinent regionThe impacts of dust storm on characteristics of aerosols and the surface layer have been analyzed [ABSTRACT FROM AUTHOR]

In sub-Saharan African countries, exposure to air pollutants, such as fine particulate matter (PM 2.5), in the residential sector is a serious environmental issue which causes health problems. Identifying the driving factors of such air pollutants is significant to formulate policies to reduce emissions and achieve a sustainable society. This study examined five socioeconomic drivers (emission intensity, the share of each energy source, energy intensity, household size, and the number of households) for energy-related air pollutants (PM 2.5 , nitrogen oxide, and non-methane volatile organic compounds) from the residential sector in Ghana and Nigeria from 1990 to 2018 using index decomposition analysis. Furthermore, we compared the similarities and differences in the driving factors of the two countries that showed different emission trends. We identified factors contributing to increasing/decreasing emissions in the two countries. In particular, the household effect is an increasing factor for both countries, while the household size effect is a decreasing factor. By contrast, the emission intensity, energy type, and energy intensity factors affect differently for the two countries. This finding suggests that energy-related policy considerably impacts the trends of air pollutant emissions from the residential sector. • Household pollutant emissions in Ghana and Nigeria are decomposed into five factors. • The household effect is their common increasing factors. • The household size effect is the common decreasing factors. • The emission intensity, energy type, and energy intensity effects affect differently. • Differences in their energy-related policies affect pollutant emission trends. [ABSTRACT FROM AUTHOR]

A new palm-sized optical PM2.5sensor has been developed and its performance evaluated. The PM2.5mass concentration was calculated from the distribution of light scattering intensity by considering the relationship between scattering intensity and particle size. The results of laboratory tests suggested that the sensor can detect particles with diameters as small as ∼0.3 µm and can measure PM2.5mass concentrations as high as ∼600 µg/m3. Year-round ambient observations were conducted at four urban and suburban sites in Fukuoka, Kadoma, Kasugai, and Tokyo, Japan. Daily averaged PM2.5mass concentration data from our sensors were in good agreement with corresponding data from the collocated standard instrument at the Kadoma site, with slopes of 1.07–1.16 and correlation coefficients (R) of 0.90–0.91, and with those of the nearest observatories of the Ministry of the Environment of Japan, at 1.7–4.1 km away from our observation sites, with slopes of 0.97–1.23 and R of 0.89–0.95. Slightly greater slopes were observed in winter than in summer, except at Tokyo, which was possibly due to the photochemical formation of relatively small secondary particles. Under high relative humidity conditions (>70%), the sensor has a tendency to overestimate the PM2.5mass concentrations compared to those measured by the standard instruments, except at Fukuoka, which is probably due to the hygroscopic growth of particles. This study demonstrates that the sensor can provide reasonable PM2.5mass concentration data in urban and suburban environments and is applicable to studies on the environmental and health effects of PM2.5. Copyright © 2018 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

To investigate transport and chemical compositions of fine aerosols in the East Asian region, aerosol chemical components and their mixing states were measured at Fukue Island in the spring of 2010. Off-line chemical analyses using an ion chromatographic analyzer and an inductively coupled plasma–mass spectrometer for the aerosols sampled by a high volume sampler have also been conducted. The mixing state and temporal variation of number concentrations of the particles containing lead (Pb) and vanadium (V) were studied by using a laser ionization single–particle aerosol mass spectrometer (LISPA-MS). The temporal variation of number concentrations of particles containing Pb measured by the LISPA-MS is well consistent with those obtained by the chemical analysis of the aerosols sampled by the high volume sampler. The Pb-containing particles were classified into four types from the statistical analysis on the basis of the single-particle mass spectra with assists of laboratory experiments. It is estimated that 52% of observed particles containing Pb were originated from coal combustion. The concentration-weighted trajectory (CWT) analysis suggests that these particles are mainly transported from China continent. The V-containing particles were classified into three types. The 41% of V-containing particles were internally mixed with sea salt and the result of CWT analysis suggests that the potentially anthropogenic V-containing particles possibility emitted from ships are mixing with sea salt in the region that is highly loaded with sea salt in the Pacific Ocean. [ABSTRACT FROM AUTHOR]