There is now enough evidence of greater frequencies and extent of fog formation in urban areas. These could easily be linked to rapid increase in aerosol number concentration (ANC) peculiar to ...polluted urban environments. It is therefore pertinent to study ANC and visibility alongside the meteorological parameters in order to investigate the relationships which may possibly exist between these parameters especially during foggy conditions. This study based on field measurements of ANC for aerosol spectrum varying from 0.3 µm to 20 µm attempts to investigates whether a threshold ANC could be associated with a given visibility range during low visibility conditions including dense fog episodes. Thus, the present work explores relationship between ANC size spectrum and visibility (100 m–4500 m) in a polluted urban environment in India with specific reference to episodes of dense fog during winter period. The study depicts a threshold minimum value of ANC during foggy conditions. A power relationship between ANC and visibility is obtained. Further, aerosol number distribution and size distribution function are also studied and empirical relation is compared with previous studies. Further work is suggested to strengthen the findings presented here.
The paper evaluates long-term (2007–2018) temporal and spatial variations in aerosol optical depth (AOD) over four major cities of India, i.e., Delhi, Kolkata, Chennai, and Jaipur, by using ...Collection 6, Moderate Resolution Imaging Spectroradiometer (MODIS) Terra and Aqua Level-3, 1°×1° gridded dataset. Annual analysis reveals a significant increasing trend from 2007 to 2018 and aerosol loading in the Indo-Gangetic Plain (IGP). Interestingly, in Northern India, i.e., Delhi, AOD values peaked during monsoon season (0.95–1.05), whereas over Kolkata, Eastern India, higher AOD is observed in winter season (0.95–1.05). Chennai, Southern India, reflects low to moderate mean AOD during all the seasons. A prominent increase in AOD percentage from 2007 to 2018 is observed over Kolkata (39%), followed by Delhi (27.34%), Chennai (26.30%), and Jaipur (16.53%). Further, cumulative effects of different meteorological parameters along with 12-year mean AOD reflected a peak in aerosol concentration (0.82 ± 0.06) over Delhi, closely followed by Kolkata (0.81 ± 0.08) and then Chennai (0.43 ± 0.03) and Jaipur (0.43 ± 0.03). Results depict a significant increase in AOD due to a wide range of anthropogenic events and call for improved policy programs to tackle the increasing AOD emissions over these megacities in India.
Present study examines how ozone concentration changed under heatwave (HW) condition with emphasis on meteorological parameters in respect to non-heatwave (NHW) days. In this perspective, Weather ...Research and Forecasting model coupled with Chemistry (WRF-Chem) has been used to simulate the surface O3 (SfO3) and maximum temperature (Tmax) during NHW (11th-19th May 2015) and HW days (21st-29th May 2015) over southeast (SE), India. The WRF-Chem simulated meteorological and chemical variables have been evaluated against the ERA5 and CAMS reanalysis dataset. A significant correlation of 55-95% is found for all the meteorological and chemical variables. The influencing parameters shows positive correlation of ozone with temperature, which reaches 75-78 ppbv under HW condition. Day to day trend analysis reveal an increasing pattern of maximum temperature and SfO3 concentration under HW condition. During HW, mixing of ozone-rich air aloft with near-surface air leading a rise in SfO3, as indicated by both ERA5 (with a maximum Planetary Boundary Layer Height (PBLH) of 1000 m) and WRF-Chem simulations (1600 m). Furthermore, the diurnal cycle of SfO3, temperature, PBLH reaches a peak at afternoon, while the other variables like nitrogen oxides (NOx), Relative Humidity (RH) shows a high concentration at night-time. Overall, WRF-Chem model effectively captures the diurnal fluctuations of SfO3, NOx and the meteorological variables during the HW event over the SE, India. Result shows that HW may cause a strong contribution to the rate of increase in SfO3 (22.17%). Thus, it is required to consider contribution of HW driven ozone when developing long-term strategies to mitigate regional ozone pollution.
The present study estimates ground-level Respirable Particulate Matter (RSPM) by the combined use of satellite remote sensing Aerosol Optical Depth (AOD) at 550 nm (AODMODIS or MODIS AOD) and ...ground-based meteorological measurements from April-2010 to March-2014 over Jaipur, semi-arid region in North-western, India.
The satellite MODIS Level 2.0 AOD is used in developing multi-regression statistical models to estimate RSPM values over the study area. The relationship between particulate matter (PM) and AOD depends on size distribution, particle composition and vertical profile of aerosols. Thus, for optimal representation of MODIS AOD, the factors like Height of Planetary Boundary Layer (HPBL) and meteorological parameters has been considered in all regression models in the present study as surrogates. The performance of regression models is analyzed on the basis of descriptive statistical measures i.e. Normalised Mean Square Error (NMSE), Correlation (R), Factor of two observations (FA2), and Fractional Bias (FB). The nonlinear multi-regression model (MODEL V) performed better than other models for our study period and region on the basis of statistical analysis (R = 0.80, NMSE = 0.01, FB = 0.0, FA2 = 100). The coefficients obtained from MODEL V were again used over Jodhpur and found to perform better than other models.
The study is further extended to find out the Air Quality Index (AQI) category over Jaipur. The average RSPM obtained from Rajasthan Pollution Control Board (RPCB) observations and those of model estimated values come under the “Moderately Polluted” category as per Indian air quality standards.
•Linear, Multi-linear, Log-linear regression models were used.•The relationship is computed between RSPM, MODIS AOD 550 nm, and meteorological parameters.•Temperature and humidity were negatively correlated with RSPM.•AOD and Wind speed were positively correlated with RSPM.•Model using the log-linear regression performs better than other models.
Urban areas are facing increasing fog frequencies that may result due to increased air pollution emanating from variety of sources. The increased pollution levels may lead to the atmospheric ...reactions resulting into the formation of secondary pollutants that may also lead to increased aerosol number concentrations (ANC) in the atmosphere. This could cause enhanced water aerosols in the presence of favourable meteorological conditions and high relative humidity. This study deals with the atmospheric pollution and visibility during winter season of megacity Delhi in order to assess the relationship between the two specifically during fog episodes. Thus, this study analyses the levels of air pollutants, aerosol spectrum and meteorological conditions during one week each in the winter season of the years 2004 and 2006 in order to have an improved understanding of their role in fog formation in mega-city Delhi. More than 300 h of measurements which included episodes of dense, thick and moderate fogs of about 25 h, were studied. The measurements cover most of the accumulation mode and greater size spectrum of aerosols. Thus, the analysis is performed for the entire period, specifically, before the fog sets up, during and afterwards. In general, the relatively small variations in number concentration show larger variations in visibility prior and post dense fog formation than during dense fog episodes. Preliminary analysis of monthly averaged RSPM (Respirable Suspended particulate Matter or PM₁₀) concentration values for four winter months for a period of 6 years (1996-2001) and visibility did not show a good correlation with total occurrences of fog. However, daily averaged RSPM concentration showed a good correlation with the occurrences of thick fog. Diurnal variation of Sulfur-dioxide and Nitrogen dioxide were found to have inverse relationship with visibility during fog which may be due to formation of secondary pollutants such as sulfate and to a lesser extent nitrates. Amongst, the daily averaged concentrations of all the criteria pollutants, RSPM was found to be best correlated with the fog in comparison to other pollutants.
Accurately determining the spatiotemporal variability of ozone on a regional to intercontinental scale is essential for air quality studies. In the present study, a first systematic evaluation and ...analysis of long-term (2009–2020) gridded datasets (0.5° × 0.625°) of total columnar ozone (TCO) retrieved from Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2
TCO
) is evaluated for the Indian region. The MERRA-2
TCO
is first validated with observations (IMD
TCO
) and then further compared with the Atmospheric Infrared Sounder (AIRS
TCO
) satellite datasets. For an in-depth comparison and statistical analysis, the dataset has been segregated into seven distinct regions, i.e., Western Himalaya (WH), North East (NE), North Central (NC), North West (NW), West Peninsula India (WPI), East Peninsula India (EPI), and South Peninsula India (SPI). Descriptive statistics (NMSE, FB, R, FA2, and d) reveals a significant correlation of MERRA-2
TCO
against IMD
TCO
for Delhi with NMSE (0.0013), FB (− 0.029) and Varanasi NMSE (0.0008), FB (− 0.014). The results of simple linear regression analysis show an increasing TCO trend value of 0.31% and 0.44% per decade in both the cities, respectively. A comparison of MERRA-2
TCO
with AIRS
TCO
shows a significant correlation of 0.62–0.87 in different regions of India. Furthermore, in support of Brewer’s circulation pattern, an increasing shift of columnar ozone from low (SPI) to high (WH) latitudinal regions is observed. Our results show that the MERRA-2 ozone dataset can be effectively used for ozone air quality studies over India and this analysis may strengthen the need for independent, high-quality, and consistent ozone measurements with small uncertainties.
A major aircraft experiment Transport and Chemical Evolution over the Pacific (TRACE-P) mission over the NW Pacific in March-April 2001 was conducted to better understand how outflow from the Asian ...continent affects the composition of the global atmosphere. In this paper, a global climate model, GEOS-Chem is used to investigate possible black carbon aerosol contributions from TRACE-P region. Our result depicts that absorbing black carbon (“soot”) significantly outflow during lifting to the free troposphere through warm conveyor belt and convection associated with this lifting. The GEOS-Chem simulation results show significant transport of black carbon aerosols from Asian regions to the Western Pacific region during the spring season. As estimated by GEOS-Chem simulations, approximately 25% of the black carbon concentrations over the western pacific originate from SE Asia in the spring.
This paper investigates aerosol properties (physical, optical and radiative) to understand the aerosol climatology (2008–17) over four Aerosol Robotic Network (AERONET) sites situated in different ...continents. For this purpose, the chosen sites are Jaipur, India in Asia, Ilorin, Nigeria in Africa, Birdsville, Queensland in Australia and White Sand, New Mexico in America. The higher AOD were found at Jaipur (AOD≈0.57; α = 0.38) during month of June and at Ilorin (AOD ≈ 1.12 and α ≈ 0.56), Africa during February. The value of SSA are also found higher i.e. 0.94 and 0.96 during the MAM over Jaipur and Ilorin respectively due to dominance of dust aerosols. Ilorin experiences the influence of harmattan winds from November to March and shows significant increase not only in coarse mode but also in fine particles fraction. While the remaining sites i.e. White Sand, America; and Birdsville, Australia are found relatively pristine based on monthly averaged AOD, AE (α) and SSA. The estimated direct radiative forcing using SBDART indicates that Ilorin and Jaipur sites in Africa-Asia exhibit much higher values of TOA and BOA as compared to White Sands and Birdsville in America-Australia. The annual averaged radiative forcing are estimated over Ilorin (38.38 ± 16.89 W m−2) and Jaipur (36 ± 8.34 W m−2). Similarly, high radiative forcing efficiency of 66.86 ± 16.69 W m−2 τ0.55nm−1 and 67.96 ± 20.46 W m−2 τ0.55nm−1 are calculated for Ilorin and Jaipur, respectively. The influence of emission differs in different continents i.e. Africa-Asia to America-Australia sites.
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•Inter-comparison of long-term AOD over desert influenced sites in different continents.•Higher SSA over Jaipur (0.94) and Ilorin (0.96) during MAM due to dustaerosols.•Harmattan winds causes higher AOD (>1.0) and VSD (0.15–0.17) over Ilorin.•ARF shows significant high values over Ilorin and Jaipur sites.•The winds and hence influence of emission differs in Africa-Asia to America-Australia sites.
A modeling effort is considered to understand the effect of dust aerosol storms in the Indian summer monsoon (ISM) onset propagation over the Indian subcontinent. The study found how the dust aerosol ...loading during the pre-monsoon period over the Indian subcontinent positively impacts the advancing ISM onset. The heavy loading of dust aerosol from middle east Asia to the northwest (NW) Indian region boosts the temperature gradient over the mid-troposphere. This sudden rise in the mid-tropospheric atmospheric temperature triggers the low-pressure belt over the monsoon trough. It amplifies the Elevated Heat Pump mechanism and loads enough dust for the dust storm over north India. The formation of the monsoon trough over the Indo-Gangetic Plain (IGP) pulls the moisture-loaded wind towards the Indian subcontinent and the IGP, followed by the onset of monsoon over Kerala within a week. Due to this storm, the intense heat gradient in the troposphere also induces the monsoon propagation and the monsoon advancement from Kerala to BoB within a short time. However, it makes up for the naturally delayed monsoon on time.
Study shows how the pre-monsoon dust storm modulates the Indian summer monsoon (ISM) propagation over the Indian region. The onset of the monsoon was delayed in a particular year, and the pre-monsoon dust storm over northwest India changed the regular monsoon mechanism and generated an entirely different mechanism. The elevated heat pump theory applies that pushes the monsoon advancement faster than usual. A dust storm over north India causes a sudden rise in the mid-tropospheric temperature gradient and more rapid monsoon advancement than usual.
•The initiation of the Indian summer monsoon is predominantly influenced by dust storms during the pre-monsoon period.•A rapid increase in the mid-tropospheric heat gradient aligns ITCZ and Hadley cell before monsoon onset.•Pre-monsoon dust storm, faster monsoon linked to elevated heat pump effect.
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