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Air pollution is a pressing issue in Delhi, with smog occurrences causing reduced visibility and various respiratory problems. A series of severe SMOG (smoke + fog) episodes between 2013 and 2017 with reduced visibility and exceptionally high PM2.5 concentrations have been reported in Delhi especially around Diwali festival (October–November). The Smog of 2016 is referred as Great Smog of Delhi. This study examined remote sensing data from 2013 to 2017 to investigate smog episodes in Delhi during pre-Diwali, post-Diwali, and Diwali. Satellite-derived parameters viz absorbing aerosol index (AAI), aerosol optical depth (AOD), and ozone monitoring instrument (OMI) along with air pollution data and climatic parameters were used to analyze smog episodes. The results showed that during smog episodes, AOD, AAI and PM2.5 concentrations exceeded permissible limits significantly at all stations across Delhi during the Diwali festival. The ground-based observations at different locations across Delhi and satellite data-derived datasets confirmed the severity of smog episodes. The findings indicate that burning of fire crackers coupled with agriculture stubble burning and subsequent transport of the smoke from North Western states through the Capital had a greater impact on deteriorating air quality in Delhi than local pollution, especially during unfavorable weather conditions associated with high humidity and weaker winds. The outcomes highlight the significance of remotely sensed information in identifying smog episodes and their severity in Delhi. It also underlines the necessity for efficient interventions to control air pollution, particularly amid festivals like Diwali.Article Highlights: Firecrackers during Diwali augmented by crop burning worsen Delhi's air quality significantly. High humidity and weak winds make smog conditions more severe and widespread. Recurrent smog episodes continued to occur despite the implementation of the Crop Residue Management Policy in 2014. [ABSTRACT FROM AUTHOR]

Aerosols absorption contributes significantly to the total radiative effects of aerosols and so an important component of radiative forcing estimates. Therefore, this study explores the spatiotemporal distribution of ultraviolet aerosol index (UVAI), future trends, potential sources of absorbing aerosols and their relationship with temperature, wind speed, precipitation and total ozone column using Ozone Monitoring Instrument retrieved UVAI and HYSPLIT model over South Asia during October 2004 to March 2022. The mean UVAI within the ranges of 0.56–1.62 are observed over Eastern and Southern Pakistan and Northern India associated with dust and biomass burning aerosols. The interannual variations in UVAI show that the values of UVAI increases from 1.73 to 3.11 during 2018–2021 over the Indo-Gangetic Plain. Contrary to this, UVAI < 0 is observed along the Karakorum and Himalaya range during 2005–2021 indicating presence of non-absorbing aerosols. The interaannual variations in UVAI reveal highest UVAI of 0.64 in December followed by 0.51 in July over South Asia. Seasonally, UVAI shows increasing trend at the rate of 0.9064 DJF−1, 0.3810 JJA−1, 0.2707 SON−1 and 0.0774 MAM−1 over South Asia. A positive correlation of 0.56 is observed between UVAI and wind speed followed by over Southern Pakistan followed 0.43 between UVAI and total ozone column Southern Pakistan and India. The UVAI shows increasing trend at the rate of 0.1409, 0.1124, 0.1224, 0.1015, 0.1242 and 0.2054 per year over Lahore, Karachi, Kanpur, New-Delhi, Varanasi, and Dhaka with maximum UVAI of 5.55, 4.47, 4.51, 4.99, 4.61 and 4.65 respectively during the study period. The anthropogenic productivity analysis reveals that primary industry and secondary industry contributes in lowering UVAI values whereas tertiary industry, energy consumption and gross domestic products increase aerosols loading in South Asia. Moreover, HYSPLIT cluster analysis further reveals the localized and trans-boundary sources of absorbing aerosols over the selected cities. [ABSTRACT FROM AUTHOR]

Particulate pollution has become a major issue in developing countries including Pakistan. Aerosols are causing severe impacts on climate and human health. To understand the effects of aerosols on the environment and human health, we must first understand their optical and physical properties. In this paper, we used ozone monitoring instrument (OMI) retrieved ultraviolet aerosol index (UVAI) to analyze spatial and temporal distribution, annual and seasonal trends of absorbing aerosols, and their relationship with meteorological parameters (e.g., temperature, relative humidity, and wind speed) over Pakistan from October 2004 to December 2021. Significant spatiotemporal changes in UVAI values were found with high values in southern and central regions and low values in northern regions of Pakistan. The mean UVAI over Pakistan showed an increasing trend of 2.89% year−1. Seasonally, UVAI increases at the rate of 3.97% winter−1, 3.24% autumn−1, 0.81% summer−1, and 0.71% spring−1. A strong positive correlation of UVAI with precipitation and temperature (~ 0.6) is observed in the central and southern regions of Pakistan. A negative and positive correlation of −0.3223 and 0.4284 of UVAI with CO2 emissions and primary industry is observed in Pakistan, respectively. We also found potential sources of aerosols over major cities of Pakistan using the Hybrid Single Particle Langrangian Integrated Trajectory (HYSPLIT) model. It determines that the dominant aerosols over Karachi are natural aerosols like sea salt and dust particles and anthropogenic aerosols are dominant over Lahore. Moreover, the natural and anthropogenic factors influencing absorbing aerosols are also discussed herein. Considering the outcomes of this study different methods would be used to reduce the concentration of particulate pollution like afforestation, efficient fuel energy consumption, promotion of public transport networks, etc. [ABSTRACT FROM AUTHOR]

The lockdown of COVID-19 pandemic has affected air quality due to the changes in human activities. Researchers worldwide observed reductions in NO2 concentrations due to lockdown and related diminished human activities, notably the reduced industrial and vehicular use. However, limited information was available for the MENA Region. In this study, the impact of lockdown due to COVID-19 on NO2 in two MENA major cities: Cairo, Egypt and Riyadh, Saudi Arabia was assessed. NO2 column was retrieved from the Ozone Monitoring Instrument (OMI) on Aura for April 2017 to 2020. The monthly mean value of NO2 concentrations of April 2017–2019 was used as a baseline. NO2 concentration in April 2020 was compared to the baseline to assess the impact of lockdown on NO2. The results demonstrated that the lockdown was associated with a reduction in NO2 in both cities. NO2 decreases by 40.3% and 23% in Riyadh and Cairo. By comparing the decrease of NO2 at weekends and weekdays, it was found that in Cairo, the decrease in weekdays (16.3%) was lower than weekends (31.9%). While in Riyadh, the decrease in weekdays (43.9%) was higher than weekends (29.3%). Variation in the reduction rates appears to be related to the different lockdown regimens taken by the two countries, among other factors. The findings of the present investigation alert countries in the region about the impact of human activities on urban air population and urge them to take appropriate mitigation measures to maintain good ambient air quality to protect human health and the environment.

The novel infectious disease (COVID-19) took only a few weeks from its official inception in December 2019 to become a global pandemic in early 2020. Countries across the world went to lockdown, and various strict measures were implemented to reduce the further spread of the infection. Although, the strict lockdown measures were aimed at stopping the spread of COVID-19, however, Its positive implications were also observed for the environmental conditions across the global regions. The present study attempted to explore the eco-restoration of coastal marine system in response to reduced deposition of atmospheric nitrogen (NO2) emission during the substantial shift in human activities across the global metropolitan cities. Remotely data of NO2 emission were taken from Ozone Monitoring Instrument and the coastal water quality along the marine system was estimated from MODIS-Aqua Level-3 using Semi-Analytic Sediment Model (SASM). The changes in tropospheric NO2 in 2020s were also compared with the long-term average changes over the baseline period 2015 − 2019. A significant reduction in anthropogenic mobility (85 − 90%) has been observed in almost all countries over different places, especially grocery, parks, workplaces, and transit stations. A massive reduction in tropospheric NO2 was detected in Wuhan (53%), Berlin (42%), London (41%), Karachi (40%), Paris (38%), Santiago (35%), and Chennai (34%) during the strict lockdown period of the early 2020 as compared to the last five years. However, after the partial lockdown was lifted, tropospheric NO2 values bounced back and slightly increased over Karachi (6%) and Bremen (12%). For water turbidity, the rate of reduction was found to be the highest along the different coastal regions of the Mediterranean Sea and Black Sea (51%), West Atlantic Ocean (32%), East Atlantic Ocean (29%), and Indian Ocean (21%) from Apr to Jun 2020. The monthly comparison of overland-runoff in 2020 compared to 2019 across the different costal watersheds indicates that the observed decline in turbidity might have been due to the reduced deposition of atmospheric nitrogen. The findings of this study suggest that the recent decline in tropospheric NO2 and water turbidity might be associated with reduced emissions from fossil fuels and road transports followed by COVID-19 forced restrictions in the twenty-first century. The inferences made here highlight the hope of improving the global environmental quality by reducing greenhouse gas emissions using innovative periodic confinement measures on heavy transport and industries while securing public health and socioeconomics.

The lockdown of COVID-19 pandemic has affected air quality due to the changes in human activities. Researchers worldwide observed reductions in NO 2 concentrations due to lockdown and related diminished human activities, notably the reduced industrial and vehicular use. However, limited information was available for the MENA Region. In this study, the impact of lockdown due to COVID-19 on NO 2 in two MENA major cities: Cairo, Egypt and Riyadh, Saudi Arabia was assessed. NO 2 column was retrieved from the Ozone Monitoring Instrument (OMI) on Aura for April 2017 to 2020. The monthly mean value of NO 2 concentrations of April 2017–2019 was used as a baseline. NO 2 concentration in April 2020 was compared to the baseline to assess the impact of lockdown on NO 2. The results demonstrated that the lockdown was associated with a reduction in NO 2 in both cities. NO 2 decreases by 40.3% and 23% in Riyadh and Cairo. By comparing the decrease of NO 2 at weekends and weekdays, it was found that in Cairo, the decrease in weekdays (16.3%) was lower than weekends (31.9%). While in Riyadh, the decrease in weekdays (43.9%) was higher than weekends (29.3%). Variation in the reduction rates appears to be related to the different lockdown regimens taken by the two countries, among other factors. The findings of the present investigation alert countries in the region about the impact of human activities on urban air population and urge them to take appropriate mitigation measures to maintain good ambient air quality to protect human health and the environment. [ABSTRACT FROM AUTHOR]

The formation of tropospheric ozone is influenced by emissions of volatile organic compounds (VOCs) and nitrogen oxides (NOx), and different regimes of sensitivity to the ozone formation have been identified depending on the concentrations of both groups of compounds. We studied the ozone formation sensitivity in the Mexico City Metropolitan Area (MCMA) using the formaldehyde to nitrogen dioxide ratio (FNR) as a proxy for the VOCs and NOx concentrations, with data retrieved from the Ozone Monitoring Instrument (OMI). To determine the different sensitivity regimes, we compared two previously established threshold values of FNR, which differ from each other in the range of ratios on which the regime transition occurs. The evaluation from 2006 to 2016 showed that the FNR gradually changed, causing variations in the ozone formation sensitivity. While in 2006, more regions were under NOx-limited/transitional regimes, in 2016, the VOC-limited conditions prevailed in most of the city. The analysis disclosed that this change is due to increasing NOx emissions in some regions of MCMA and decreasing VOC emissions in other areas. The observed trend is different from that in major cities in other parts of the world, such as the United States, where ozone formation sensitivity has moved towards NOx-limited conditions. Therefore, reducing VOC emissions would be a suitable approach for decreasing tropospheric ozone concentrations in the MCMA.

Aerosol index (AI) is qualitatively indicating the presence of suspended aerosol particles in the air. The major sources of these particles are desert dust, biomass burning, and volcanic ash plumes. The AI observations derived from the ozone monitoring instrument (OMI) on Aura satellite were analyzed over Iraq for the period 2005–2018. The results showed that the long-term spatiotemporal distribution of AI was significantly variable, with lower values (< 1.5) at the north mountain area and western highland and higher at the central and southern parts of the country. Two distinct spots of very high AI were observed over the two major source areas of dust storms, in the northwest and south of Iraq. In general, AI was increasing from northwest to south and southeast suggesting that the main source of the aerosols is regionally not locally and coming from west and northwest side. The results also indicated that AI has an annual cycle over the entire country: minimum in winter (< 0.5 during January in the northeast) and maximum in summer (~ 4.0 during June in the south). The analysis of monthly AI revealed that maximum monthly AI (= 4.1) occurred in the northwestern town of Anah and the minimum AI (~ 0) happened in the northern city of Mosul. Statistical test of AI seasonal time series exhibited a significant decreasing trend in AI in the central and southern parts of the country. Analysis of daily AI showed that annual number of days with AI > 2 may reach more than 140 days in Basra and more than 90 in Anah and Baghdad. Comparisons of Moderate Resolution Imaging Spectroradiometer (MODIS) true color images and AI for five different types of dust storms occurred over Iraq showed that AI is maximum at the core of the storm and the gradation of decreasing AI was consistent with the spread of dust out of the core. Maximum AI was > 5.5 during summer Shamal storm, > 3.0 during winter Shamal and frontal cases, and > 2.0 for the Haboob case. The HYSPLIT trajectories calculations showed that the dust plume in the MODIS image was significantly similar to the computed trajectories and the majority of air masses were coming from north and northwest. [ABSTRACT FROM AUTHOR]

La Dosis Eritemática Diaria (EDD) y el Índice UV (UVI) al mediodía obtenidos con el Ozone Monitoring Instrument (OMI), a bordo del satélite Aura de la NASA, han sido validados para el periodo 2005-2013 utilizando medidas con base en tierra en 5 estaciones diferentes de la costa mediterránea: Murcia, Valencia, Palma de Mallorca, Barcelona y Roma (donde sólo se tienen medidas del UVI al mediodía). Las medidas con base en tierra fueron realizadas con radiómetros YES UVB-1 en Murcia, Valencia, Palma de Mallorca y Barcelona, y con un espectrofotómetro Brewer MKIV en Roma. La evolución de la EDD muestra un claro comportamiento estacional en todas las localidades, tanto para los datos de suelo como para los satelitales, con valores máximos en verano (junio y julio) y valores mínimos en invierno (diciembre y enero). Los resultados de la validación muestran una buena correlación entre los datos satelitales y las medidas con base en tierra, aunque las del OMI sobreestiman las de los instrumentos de suelo. Las diferencias entre ambos conjuntos de medidas es máxima para los meses de primavera y verano y mínima en los meses de otoño e invierno. Un elevado porcentaje de casos (>80%) presenta diferencias mínimas (0 ó 1 unidades) entre el UVI obtenido con el OMI y el obtenido con los instrumentos de suelo para todas las estaciones de medida. En todas ellas se alcanzan valores del UVI altos (6-7) o muy altos (8-10) en un elevado porcentaje de los días del periodo analizado, pero apenas se alcanzan valores del UVI extremos (≥11).

This paper focus on study the variations of monthly tropospheric NO2 concentrations over three Iraqi cities Baghdad (33.3° N, 44.4° E), Basrah (30.56° N, 47.8° E) and Erbil (36.3° N, 44.06° E). Monthly NO2 retrievals from the Ozone Monitoring Instrument (OMI) onboard Aura satellite during the period from October 2004 to March 2013 have been used. The results show a high monthly and annual NO2 concentrations at Baghdad than Basra and Erbil may be attribute to high densely populations and a high economic activity. During the whole period, Baghdad, Basrah and Erbil were exhibited an average of NO2 (8.1±2.5), (3.7±1.3) and (3.3±1.7) in unit 1015 molecules/cm2 respectively. The maximum concentration of NO2 is found in winter season in all year due to enhancement of atmospheric photochemistry. An elevated trend of NO2 concentration is found in study sites where maximum annual increase in NO2 is found at Erbil (11.53 % per year), Basrah (8.59 % per year) and Baghdad (7.42 % per year). A statistical study is needed to evaluate the economic activity in Iraqi cities to understand the reason of growing the air pollution over Iraqi cities.

Abstract Recursive skeletonization factorization techniques can evaluate an accurate approximation to the log-likelihood for irregularly sited two-dimensional spatial data under a Gaussian process in O (n 3 ∕ 2) time and O (n log n) storage. We demonstrate the application of these techniques to data on the surface of a sphere by fitting a Matérn model to approximately 87,000 total column ozone observations obtained from a single orbit of a polar-orbiting satellite. We then demonstrate that this fit can be improved by allowing either the range or scale parameters of the process to vary with latitude, but that the latter form of nonstationarity can be accommodated using skeletonization factorizations that do not need to be redone when optimizing over the parameters describing nonstationarity. [ABSTRACT FROM AUTHOR]

The widespread distribution and strong seasonal pattern of highly concentrated summertime formaldehyde (HCHO) were observed using data from the Ozone Monitoring Instrument (OMI) onboard Aura satellite from 2005 to 2015 in Beijing-Tianjin-Hebei, China. The large-scale HCHO concentrations and its close connection with the surface O3 pollution made the study of summertime HCHO patterns and its major contributors necessary. Accordingly, time series decomposition, Moran's I and Pearson correlation coefficient (PCC) were adopted to investigate the spatiotemporal variations of HCHO. We found that the HCHO columns regionally increased from 2005 to 2010 and decreased in the north (e.g., Chengde) from 2010 to 2015. Additionally, HCHO Vertical Column Densities (VCDs) exhibited higher values in urban areas. Despite the strong possibilities of major biogenic contributions, anthropogenic sources represented larger spatial PCCs and larger total emission rates. Industrial sources exhibited a large increasing emission amount, and the most similar distribution to HCHO was found in residential sources. By comparison, power-based emissions accounted for a relatively small fraction, and transportation emissions declined rapidly. In conclusion, anthropogenic VOCs might contribute to the summertime HCHO concentrations as well as isoprene, and controls on VOCs and HCHO would be greatly assisted by the satellite-based observations. [ABSTRACT FROM AUTHOR]