Variability of SO₂, CO, and light hydrocarbons over a megacity in Eastern India: effects of emissions and transport

A 1-D model to retrieve the vertical profiles of minor atmospheric constituents for cloud microphysical modelling: III. Disturbed weather situations

A hybrid Monte-Carlo Gear solver developed earlier has been improvised to retrieve the vertical profiles of CH4 and N2O during disturbed weather situations such as western disturbances, tropical cyclones, and heavy rainfall events over the megacities: Delhi, Kolkata, Chennai, and Mumbai. Due to rapid changes in the temperature during the passage of these systems over megacities, the percentage differences of CH4 and N2O number concentrations were more compared to the Community Long-term Infrared Microwave Coupled Atmospheric Product System (CLIMCAPS). Therefore, the hybrid solver has been modified by improving maximum likelihood estimates of vertical temperature profiles. The number concentrations of CH4 and N2O during these weather events since 2012 are obtained from the CLIMCAPS dataset for bias correction. It is found that the modified methodology has improved the retrieval of CH4 and N2O vertical profiles by reducing the error percentages during daytime and nighttime over these megacities. The percentage error in estimated number concentrations of CH4 and N2O significantly reduced during (i) the passage of the western disturbance and rainy days of August 2020 over Delhi; (ii) the rainy days of June 2020 over Kolkata; (iii) the influence of supercyclonic storm Amphan (24 and 25 Nov 2020) over Chennai and (iv) rainy days of July 2020 over Mumbai. Implementing this solver in the global model may retrieve the number concentrations more accurately.

Interpreting the COVID effect on atmospheric constituents over the Indian region during the lockdown: chemistry, meteorology, and seasonality

Most of the published articles which document changes in atmospheric compositions during the various lockdown and unlock phases of COVID-19 pandemic have made a direct comparison to a reference point (which may be 1 year apart) for attribution of the COVID-mediated lockdown impact on atmospheric composition. In the present study, we offer a better attribution of the lockdown impacts by also considering the effect of meteorology and seasonality. We decrease the temporal distance between the impacted and reference points by considering the difference of adjacent periods first and then comparing the impacted point to the mean of several reference points in the previous years. Additionally, we conduct a multi-station analysis to get a holistic effect of the different climatic and emission regimes. In several places in eastern and coastal India, the seasonally induced changes already pointed to a decrease in PM concentrations based on the previous year data; hence, the actual decrease due to lockdown would be much less than that observed just on the basis of difference of concentrations between subsequent periods. In contrast, northern Indian stations would normally show an increase in PM concentration at the time of the year when lockdown was effected; hence, actual lockdown-induced change would be in surplus of the observed change. The impact of wind-borne transport of pollutants to the study sites dominates over the dilution effects. Box model simulations point to a VOC-sensitive composition.

Characteristics and health risk assessment of fine particulate matter and surface ozone: results from Bengaluru, India

Urban air pollution is a complex problem, which requires a multi-pronged approach to understand its dynamics. In the current study, various aspects of air pollution over Bengaluru city were studied utilizing simultaneous reference-grade measurements (during the period July 2019 to June 2020) of fine particulate matter mass concentration (PM_2.5), aerosol black carbon mass concentrations (BC), and surface ozone (O₃) concentrations. The study period mean PM_2.5, BC, and O₃ were observed to be 26.8 ± 11.5 µg m^-3, 5.6 ± 2.8 µg m^-3, and 25.5 ± 12.4 ppb, respectively. Statistical methods such as principal component analysis, moving average subtraction method, conditional bivariate probability function, and concentration weighted trajectory analysis were performed to understand the dynamics of air pollution over Bengaluru and its long-range transportation pathways. Some of the major findings from the statistical analyses include (i) contrasting association in BC versus O₃ and PM_2.5 versus O₃; (ii) around one-fourth of the observed receptor site BC was contributed by local sources/emissions; and (iii) the source locations potentially contributing to BC and PM_2.5 were spatially different. In Bengaluru, long-term exposure to PM_2.5 resulted in around 3413, 3393, 1016, and 147 attributable deaths for the health endpoints chronic obstructive pulmonary disorder, ischemic heart disease, stroke, and lung cancer, respectively. Long-term exposure to O₃ resulted in around 155 attributable deaths for respiratory diseases, as estimated by the AirQ + model. Finally, the limitations of the study in terms of data availability and analysis have been detailed.

Performance analysis and optimization of solar-powered E-rickshaw for environmental sustainability in rural transportation

The last mile connectivity through public transport is a challenging task in India. However, according to the Society of Indian Automotive Manufacturers (SIAM) statistics, three-wheelers sales increased by 10.27% in the year financial year of 2018-2019 compared to the previous financial year. In this growth, it is recorded that the passenger carrier three-wheeler sales increased by 10.62% and goods carrier three-wheeler grew by 8.75% in the year 2019 compared to the previous year. The existing design consideration in the three-wheeler development shows poor performance in the real-world scenario because the three-wheeler's open drive compartment creates more aerodynamic drag to the vehicle. This increases the amount of energy consumption to achieve the same amount of range (km/L). Three-wheeler's extra energy consumption will directly increase the amount of exhaust emission in internal combustion engines and electrical energy consumption in electric vehicles. The present paper attempts in designing a solar-powered electrical auto-rickshaw for rural transportation. The paper aims to obtain an optimal solar module placement angle and analyzes the solar-powered electrical auto-rickshaw performance by incorporating the National Advisory Committee for Aeronautics (NACA) aerodynamic design principles. The optimal solar module placement angle is identified by analyzing the various configurations like front alone tilt at 16°-degree, rear alone tilt at the 5°-degree and combined front at 16°-degree, and rear at 5°-degree to reduce the aerodynamic drag effect. The paper also aims to identify the effect of the optimal angle on vehicle speed, and solar power generation to enhance the performance and energy efficiency for achieving environmentally sustainable transportation.

Pandemic induced lockdown as a boon to the Environment: trends in air pollution concentration across India

The present paper designed to understand the variations in the atmospheric pollutants viz. PM₁₀, PM_2.5, SO₂, NO₂, and CO during the COVID-19 pandemic over eight most polluted Indian cities (Mumbai, Delhi, Bangalore, Hyderabad, Lucknow, Chandigarh, Kolkata, and Ahmedabad). A significant reduction in the PM_2.5 (63%), PM₁₀ (56%), NO₂ (50%), SO₂ (9%), and CO (59%) were observed over Major Dhyan Chand Stadium. At Chhatrapati Shivaji International Airport, a decline of 44% in PM_2.5 and 50% in PM₁₀ was seen just a week during the initial phase of the lockdown. Gaseous pollutants (NO₂, SO₂ & CO) dropped up-to 36, 16, and 41%, respectively. The Air Quality Index (AQI) shows a dramatic change from 7% to 67% during observation at Chandigarh and Ballygunge during the inspection. Whereas, Ahmedabad, Worli, Income Tax Office, Talkatora, Lalbagh, and Ballygaunge have showed a significant change in AQI from 25.76% to 68.55%. However, Zoo Park, CST, Central School, and Victoria show relatively low variation in AQI in the range of 3.0% to 14.50% as compare to 2019 after lockdown. Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) analysis suggested that long range transportation of pollutants were also a part and parcel contributing to changes in AQI which were majorly coming from the regions of Iran, Afghanistan, Saudi Arabia, as well as a regional grant from Indian Gangatic plains and Delhi Non-capital region.

Multi-Model Evaluation of Meteorological Drivers, Air Pollutants and Quantification of Emission Sources over the Upper Brahmaputra Basin

The temporal distributions of meteorological drivers and air pollutants over Dibrugarh, a location in the upper Brahmaputra basin, are studied using observations, models and reanalysis data. The study aims to assess the performance of the Weather Research and Forecasting model coupled with chemistry (WRF-Chem), the WRF coupled with Sulfur Transport dEposition Model (WRF-STEM), and Copernicus Atmosphere Monitoring Service (CAMS) model over Dibrugarh for the first time. The meteorological variables and air pollutants viz., black carbon(BC), carbon monoxide(CO), sulphur dioxide(SO2), Ozone(O3), and oxides of Nitrogen(NOx) obtained from WRF-Chem, WRF-STEM and CAMS are evaluated with observations. The source region tagged CO simulated by WRF-STEM delineate the regional contribution of CO. The principal source region of anthropogenic CO over Dibrugarh is North-Eastern India with a 59% contribution followed by that from China (17%), Indo-Gangetic Plains (14%), Bangladesh (6%), other parts of India (3%) and other regions (1%). Further, the BC-CO regression analysis is used to delineate the local emission sources. The BC-CO correlations estimated from models (0.99 for WRF-Chem, 0.96 for WRF-STEM, 0.89 for CAMS), and reanalysis (0.8 for Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA2) are maximum in pre-monsoon whereas surface observations show highest correlations (0.81) in winter. In pre-monsoon season, 90% of the modeled CO is due to biomass burning over Dibrugarh.

Ambient black carbon, PM2.5 and PM10 at Patna: Influence of anthropogenic emissions and brick kilns

Particulate Matters like Black Carbon, PM_2.5 and PM₁₀ present in the atmosphere not only poses a threat to human health but also contributes to near-term regional and global atmospheric warming. There has been a large concern of this kind of pollutants in Indo-Gangetic Plains (IGP). Hence, an attempt has been made to see the impact in one of the highly developing city of IGP as Patna. This city has been ranked among the top 100 air polluted cities in the world. To establish the role of BC, PM_2.5, and PM₁₀ on local air quality, continuous measurements were conducted at seven locations of Patna from January to December 2015. The seasonal mass concentration of BC were 13.92±3.48μgm^-3 in the winter, 9.65±3.0μgm^-3 in the pre-monsoon, 5.83±1.90μgm^-3 in the monsoon and 7.86±3.66μgm^-3 in the post-monsoon. Similarly, the seasonal concentrations of PM_2.5 (PM₁₀) were 68.86±18.83μgm^-3 (108.13±21.49μgm^-3) in the winter; 64.62±18.76μgm^-3 (93.45±18.42μgm^-3) in the pre-monsoon; 37.83±11.27μgm^-3 (62.82±14.81μgm^-3) in the monsoon and 40.14±16.66μgm^-3 (64.72±22.40μgm^-3) in the post-monsoon. About 76.67% of PM_2.5 and 87.78% of PM₁₀ concentrations were greater than NAAQ Standards in the winter on a daily basis and 46.74% and 36.96% in the pre-monsoon season. The backward trajectory analysis was also carried out through HYSPLIT model which suggests that the additional source of these pollutants during the winter and pre-monsoon season from the northwest and northern region of Patna. The ratios of PM₁₀/PM_2.5 observed at brick kilns cluster monitoring locations during the brick manufacturing period were significantly higher (0.87-4.48μgμgm^-3) than other monitoring sites and increase the level of these pollutants over the city.

Ambient particulate matter and carbon monoxide at an urban site of India: Influence of anthropogenic emissions and dust storms

Continuous measurements of PM_2.5, PM₁₀ and CO were conducted at an urban site of Udaipur in India from April 2011 to March 2012. The annual mean concentrations of PM_2.5, PM₁₀ and CO were 42 ± 17 μg m^-3, 114 ± 31 μg m^-3 and 343 ± 136 ppbv, respectively. Concentrations of both particulate and CO showed high values during winter/pre-monsoon (dry) period and lowest in the monsoon season (wet). Local anthropogenic emission and long-range transport from open biomass burning sources along with favourable synoptic meteorology led to elevated levels of pollutants in the dry season. However, higher values of PM₁₀/PM_2.5 ratio during pre-monsoon season were caused by the episodes of dust storm. In the monsoon season, flow of cleaner air, rainfall and negligible emissions from biomass burning resulted in the lowest levels of pollutants. The concentrations of PM_2.5, PM₁₀ and CO showed highest values during morning and evening rush hours, while lowest in the afternoon hours. In winter season, reductions of PM_2.5, CO and PM₁₀ during weekends were highest of 15%, 13% and 9%, respectively. In each season, the highest PM_2.5/PM₁₀ ratio coincided with the highest concentrations of pollutants (CO and NO_X) indicating predominant emissions from anthropogenic sources. Exceptionally high concentrations of PM₁₀ during the episode of dust storm were due to transport from the Arabian Peninsula and Thar Desert. Up to ∼32% enhancements of PM₁₀ were observed during strong dust storms. Relatively low levels of O₃ and NO_x during the storm periods indicate the role of heterogeneous removal.

Secondary Organic Aerosol Formation over Coastal Ocean: Inferences from Atmospheric Water-Soluble Low Molecular Weight Organic Compounds

A lack of consensus on the distributions and formation pathways of secondary organic aerosols (SOA) over oceanic regions downwind of pollution sources limits our ability to assess their climate impact globally. As a case study, we report here on water-soluble SOA components such as dicarboxylic acids, oxocarboxylic acids, and α-dicarbonyls in the continental outflows from the Indo-Gangetic Plain (IGP) and Southeast Asia (SEA) to the Bay of Bengal. Oxalic acid (C₂) is the dominant species followed by succinic (C₄) and glyoxylic acids (ωC₂) in the outflow. Nonsea-salt SO₄^2- also dominates (∼70%) total water-soluble inorganic constituents and correlates well with aerosol liquid water content (LWC) and C₂, indicating their production through aqueous phase photochemical reactions. Furthermore, mass ratios of dicarboxylic acids (C₂/C₄, C₂/ωC₂), and their relative abundances in water-soluble organic carbon and total organic carbon are quite similar between the two continental (IGP and SEA) outflows, indicating the formation of SOA through aqueous phase photochemical reactions in LWC-enriched aerosols, largely controlled by anthropogenic SO₄^2-.

Variability of atmospheric carbonyl sulfide at a semi-arid urban site in western India

Atmospheric carbonyl sulfide (COS) is a major precursor for sulfate aerosols that play a critical role in climate regulation. Recent studies have highlighted the importance of COS measurements as a reliable means to constrain biospheric carbon assimilation. In a scenario of limited availability of COS data around the globe, we present gas-chromatographic measurements of atmospheric COS mixing ratios over Ahmedabad, a semi-arid, urban region in western India. These measurements, being reported for the first time over an Indian site, enable us to understand the diurnal and seasonal variation in atmospheric COS with respect to its natural, anthropogenic and photochemical sources and sinks. The annual mean COS mixing ratio over Ahmedabad is found to be 0.83±0.43ppbv, which is substantially higher than free tropospheric values for the northern hemisphere. Inverse correlation of COS with soil and skin temperature, suggests that the dry soil of the semi-arid study region is a potential sink for atmospheric COS. Positive correlations of COS with NO2 and CO during post-monsoon and the COS/CO slope of 0.78pptv/ppbv reveals influence of diesel combustion and tire wear. The highest concentrations of COS are observed during pre-monsoon; COS/CO2 slope of 44.75pptv/ppmv combined with information from air mass back-trajectories reveal marshy wetlands spanning over 7500km(2) as an important source of COS in Ahmedabad. COS/CO2 slopes decrease drastically (8.28pptv/ppmv) during post-monsoon due to combined impact of biospheric uptake and anthropogenic emissions.

Analysis of ambient formaldehyde in the eastern region of India along Indo-Gangetic Plain

Ambient levels of formaldehyde (HCHO) were measured in the tropical urban mega city of Kolkata from July 2012 to April 2014, based on USEPA Compendium Method TO-11A using 2,4-dinitrophenylhydrazine (2,4-DNPH). The samples were analyzed by isocratic reverse-phase high-performance liquid chromatography (HPLC) with an ultraviolet detector at a wavelength of 360 nm. High values of HCHO were recorded at our site. The highest and average HCHO mixing ratio measured for the entire study period was 803 and 217 ppbv respectively. Seasonal wind regimes have been found to influence the seasonal pattern of HCHO mixing ratio at this site resulting in relatively higher mixing ratio of HCHO during the pre-monsoon periods as compared to the others. Apart from these, sampling-based measurements of CH4 and continuous measurements of ozone (O3) and CO were also performed with the objective to study the interrelationship of HCHO with these species. The results suggest the presence of highly complex chemistry among them.