Asian Atmospheric Pollution: Sources, Characteristics and Impacts

Asian Atmospheric Pollution: Sources, Characteristics and Impacts provides a concise yet comprehensive treatment of all aspects of pollution and air quality monitoring, across all of Asia. It focuses on key regions of the world and details a variety of sources, their transport mechanism, long term variability and impacts on climate at local and regional scales. It also discusses the feedback on pollutants, on different meteorological parameters like radiative forcing, fog formations, precipitation, cloud characteristics and more. Drawing upon the expertise of multiple well-known authors from different countries to underline some of these key issues, it includes sections dedicated to treatment of pollutant sources, studying of pollutants and trace gases using satellite/station based observations and models, transport mechanisms, seasonal and inter-annual variability and impact on climate, health and biosphere in general.

Asian Atmospheric Pollution: Sources, Characteristics and Impacts is a useful resource for scientists and students to understand the sources and dynamics of atmospheric pollution as well as their transport from one continent to other continents, helping the atmospheric modelling community to model different scenarios of the pollution, gauge its short term and long term impacts across regional to global scales and better understand the ramifications of episodic events.

• Covers all of Asia in detail in terms of pollution
• Focuses not only on local pollution, but on long-term transport of these pollutants and their impacts on other regions as well as the globe
• Includes discussion of both particulate matter and greenhouse gases
• Serves as a single resource on Asian air pollution and Impacts from the most current research across the globe including the US, Asia, Africa and Europe

• Language: English
• Publisher: Elsevier Science
• Release date: Aug 31, 2021
• ISBN: 9780128166949

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Chapter 1: Sources of atmospheric pollution in India

Ramesh P. Singha; Akshansha Chauhanb    a School of Life and Environmental Sciences, Schmid College of Science and Technology, Chapman University, Orange, CA, United States

b Center for Space and Remote Sensing Research, National Central University, Taoyuan, Taiwan

Abstract

India with 28 states and 8 union territories has diversified weather conditions, and is a home to 1.389 billion people. India is surrounded by the Bay of Bengal in the east, the Arabian Sea in the west, and the Indian Ocean in the south. In the northern part, the Indo-Gangetic Plain (IGP) lies between the Indian shield and the Himalayan region. The IGP is one of the agriculturally productive regions with fertile land and good groundwater resources. About 900 million people live in the IGP, the westerly winds are dominant in the northern parts, which brings pollutants from the neighboring countries and the outflow from the IGP reaches over Bangladesh and beyond. The outflow of pollutants also reaches toward the Himalayan regions and the pollutants especially at the time of forest fires impact the IGP region. The northern flank of India is surrounded by the towering Himalayas. The western part is adjacent to the neighboring country Pakistan, and between IGP and the eastern side, Bangladesh is located. In the northern part of India including IGP, all the four seasons (winter, summer, monsoon, and premonsoon) with contrasting weather conditions are observed. The region experiences extreme weather conditions, and all the major cities are known for high atmospheric pollution and poor air quality throughout the year and contrasting seasonal differences. In this chapter, an overview of atmospheric pollution and poor air quality and their dynamics are presented.

Keywords

Atmospheric pollution; Air quality; Sources of pollution; Satellite remote sensing; Coal-based power plants; Brick kilns; Crop residue burnings

1: Introduction

The atmospheric pollution and poor air quality are attributed to the population. India and China, two major countries of the world, occupy about one-third of world population. These countries and other countries such as Pakistan, Bangladesh, and Nepal are the major contributors to atmospheric and air pollution in the Asian countries. In the last two decades, due to rapid economic growth in the Asian countries, the pollution level has increased. In India, the census data is updated every 10 years and the current population of India is about 1.38 billion (up to December 2020); the decadal growth of Indian population is shown in Fig. 1 (source: https://www.censusindia.gov.in). The growing population is the main cause of pollution, all the anthropogenic activities, industrialization, and energy demands are very much associated with the population.

Fig. 1

Fig. 1 Decadal population growth in India ( https://www.censusindia.gov.in ), the current population of India is about 1.38 billion. In 2021, the census data will be updated. Source of data 1900–2011, Census of India: Office of the Registrar General and Census Commissioner, India.

Fig. 2 shows Google image of India, surrounded by ocean on three sides, the northern parts of India is surrounded by the towering Himalayas and Nepal. The northwest side of India is surrounded by Pakistan and Afghanistan, and the northeastern parts of India are surrounded by Bangladesh, Myanmar, Thailand, and Vietnam (Fig. 2). The emissions by human and anthropogenic activities, vehicles, industries, coal-based power plants, and brick kilns contained only over India; the outflow of emissions influence Indian coastal areas, surrounding ocean water, and neighboring Bangladesh, whereas the emissions from the neighboring countries adjacent to western parts of India and southeastern neighboring countries influence the atmospheric pollution loading over India. During winter season, the anthropogenic activities in Pakistan affect the atmospheric pollutants over the Indo-Gangetic Plains (IGP) and depending on the meteorological conditions, pollutants move in the IGP which is a valley due to low terrains. During premonsoon season, the long-range transport of dust brings dust over the IGP, affecting the weather conditions and visibility.

Fig. 2

Fig. 2 Google image showing India surrounded by ocean on three sides. The northern parts are surrounded by the towering Himalayas and Nepal. The northwest side of India is surrounded by Pakistan and Afghanistan, the northeastern parts of India is surrounded by Bangladesh, Myanmar, Thailand, and Vietnam.

The atmospheric pollution and poor air quality especially in the northern parts of India become apparent especially during winter season. The northern parts of India, especially the IGP, are densely populated; human activities are the sources of atmospheric pollution. Besides population, the following activities are the sources of atmospheric pollution in India:

–anthropogenic activities

–biofuel cooking

–biomass burning

–brick kilns

–burning of dead bodies

–burning of wood especially during winter season

–coal-based thermal power plants.

–crop residue burning

–cyclone activities in the Bay of Bengal

–diesel boats in the rivers

–diesel generators

–factories

–forest fires

–garbage burning

–grass burning in the hilly areas

–heating of houses

–mining especially in the eastern parts of the IGP

–rice mills

–road construction activities

–road dust and long-range transport of dust

–underground coal fires

–vehicular emissions

In recent years, the agricultural activities have grown due to the growing demand for food, which have also contributed to atmospheric pollution and poor air quality. Following are the adverse impacts of pollution:

–poor air quality

–deteriorating human health

–changing weather conditions

–uneven distribution of monsoon rainfall

–rapid snow/glaciers melting

–poor visibility

–impact on ocean ecology

–low agricultural productivity

–danger of acid rain

The atmospheric pollution and air quality also causes ozone depletion, reduction in biodiversity, economic losses, precipitation, changes in monsoon, and air and land pollution, which lead to Global Change and Global warming (Fig. 3). The poor visibility during winter season, especially in the northern parts of India, when the buses and trains are reported running late, attracts attention of common people. The poor visibility is caused by dense haze, fog, and smog especially in Kanpur city (Kanpur longitude 80.20°E and latitude 26.26°N), which is in the center of the IGP. This city is one of the industrial cities known for textile industries. The Indian Institute of Technology Kanpur, one of the excellent academic institutions, was started in collaboration with the American universities in 1962. Kanpur city with 3.2 million people is situated in the southern flank of the central part of the IGP. The IGP is one of the agriculturally productive regions with largest drainage in the world and is bordered by the towering Himalayas in the north and Vindhya-Satpura ranges in the south. The IGP is traversed by two main rivers, Ganga and Yamuna and their tributaries. In the last four decades, due to growing urbanization and economic growth, the rural population tend to move to the urban areas, especially in India, China, and other Asian countries.

Fig. 3

Fig. 3 Impacts of the atmospheric and air pollution. Courtesy: A.K. Prasad.

Due to growing population, especially in the IGP, in the last four decades, all kinds of demands have increased many folds for the people living in India to have good and comfortable life along with the industries and dense transport network. As a result of the migration of people from rural to urban areas, urban areas expanded, industries developed, and dense road work and dense transport increased, which resulted in an increase in atmospheric pollution and the urban and surrounding areas suffered from poor air quality. The dense fog, smog, and haze over the IGP were first time observed by the ADEOS POLDER satellite (Goloub et al., 2001). The limited POLDER data clearly shows very high aerosol optical depth (Fig. 4) over the IGP especially during winter season (Goloub et al., 2001). The large amount of aerosol loading over the IGP is the cause of dense fog, haze, and smog during winter season; during this period visibility is very low resulting in trains running late or the cancellation of trains (Goloub et al., 2001; Di Girolamo et al., 2004; Massie et al., 2004; Gautam et al., 2007, 2013; Prasad and Singh, 2007a).

Fig. 4

Fig. 4 ADEOS-1 Polder image showing pollution over the northern parts of India ( Goloub et al., 2001).

With the booming of the economic conditions, people started having two and four wheelers and slowly density of vehicles on the road increased many folds in the last decades. The normal time to commute a small distance of 17 km from the Indian Institute of Technology Kanpur campus to the Kanpur Railway station during daytime increased from 20 min to even 90 min by car.

The growing population, the land use/land cover, and density of industries in the northern parts of India, especially in the IGP, increased many folds in the last 40 years, as a result the pollution level enhanced which was reflected from the cloudy conditions due to high air pollution during daytime and due to poor visibility less than 5 m due to dense fog in the late evening (after 10 pm) during winter season. The fog, haze, and smog are very dynamic in nature, and swing in the IGP valley from west to east depending on the meteorological conditions (Fig. 5).

Fig. 5

Fig. 5 MODIS images from December 20–23, 2002 showing movement of fog over the Indo-Gangetic Plains depending on the favorable meteorological conditions. Source: NASA Worldview.

In the northern parts of India, generally, westerly winds are dominant, which brings pollutants from the western parts of India and from the neighboring countries in the western side. During winter season smoke plumes from crop burning in the western parts and during premonsoon season, long-range transport of dust blankets over the IGP and beyond, and at many places in the IGP (Fig. 6). The whole northern parts are one of the most polluted areas. The lead (Pb) concentration in the atmosphere over the IGP is found to be very high; recently, Salam et al. (2008) found a decreasing trend in Dhaka due to the ban on the use of leaded fuel. The overall trace metal concentrations of Pb, Zn, Cu, Fe, As, and Cd in Dhaka was higher than those found in European (e.g., Spain, Norway) and East Asian (e.g., Taiwan) locations, but lower than those measured in the Southeast Asia.

Fig. 6

Fig. 6 Spatial variations of wind rose diagrams showing wind directions in major cities—the rose diagram. The rose diagram was overlaid on MODIS Terra satellite image of January 1, 2007. Courtesy: A.K. Prasad.

During winter season the fog, smog, and haze move in the IGP valley, causing poor visibility. The human activities in the IGP cause huge amount of particulate matters and trace gas emissions (Di Girolamo et al., 2004; Jethva et al., 2005; Prasad et al., 2006a; Gautam et al., 2007, 2010; Nair et al., 2007; Kar et al., 2008, 2010; Balakrishnan et al., 2011; Shaiganfar et al., 2011; Ghude et al., 2011, 2012; Ghosh et al., 2013). In general, the atmospheric aerosol loading is very high in the Asian countries. The indoor and outdoor human activities (Fig. 7) in the Asian countries including India are the main causes of the atmospheric aerosol loading and poor air quality. In the last two decades, several ground-based aerosol monitoring stations have been established in East and Southeast Asia, and the long-term measurements of aerosol climatology have been reported by Merrill and Kim (2004) for East Asia and India (Di Girolamo et al., 2004; Dey and Di Girolamo, 2010). Fig. 7 shows the cause of indoor and outdoor atmospheric pollution in rural areas. To curb the air pollution due to biofuel burning in villages, the Government of India under Ujjawala Yojana promoted the use of liquefied petroleum gas (LPG) for cooking to improve the air quality.

Fig. 7

Fig. 7 (A) Burning of wood and coal for cooking purpose in the rural area. (B) The right panel image shows the production of jaggery at a local crusher in Indian village.

Extensive use of biofuels in the rural area, biomass burning, and emissions from power plants and industries are the sources for the formation of more CO, NOx, O3, HC, and other secondary pollutants in this region (Prasad et al., 2006b; Badarinath et al., 2009). The pollution level has increased over the IGP, which has a direct impact on climatic conditions, enhances haze, fog, and cloudy conditions especially during the winter season (Di Girolamo et al., 2004). The major pollutants in the IGP are sulfate aerosols due to growing anthropogenic activities (Sharma et al., 2003). In the northern parts of India, suspended particulate matter concentration is higher during the summer season than during the winter season, reducing the neutralization capacity of the atmosphere (Sharma et al., 1994). The recent Central Pollution Control Board (CPCB) measurements have shown very high annual average concentrations (> 210 mg/m³, in the critical range compared to the air quality standard in India) of particulate matter of diameter less than 10 mm (PM10) in the atmosphere of the major cities of the IGP (http://www.cpcbenvis.nic.in/annual_report/AnnualReport_7_annualreport2002-03.pdf). In addition to the urban-industrial pollution, desert dust is another major source of aerosols over the IGP (Dey et al., 2004; Prasad and Singh, 2007a).

Several studies have been carried out using satellite observations and chemical transport model simulations to characterize O3 (both surface and atmospheric) over the IGP (Di Girolamo et al., 2004; Jain et al., 2005; Ghude et al., 2006, 2008; Kunhikrishnan et al., 2006; Beig and Ali, 2006; Roy et al., 2008; Ojha et al., 2012). Beig and Brasseur (2006) established an emission inventory of tropospheric ozone over IGP using a chemical transport model and have studied changes in pollutant trace gases. Kar et al. (2008, 2010) used multisatellite data to study carbon monoxide (CO) and tropospheric ozone (TO) distributions particularly over the eastern parts of IGP. Ghude et al. (2011) studied regional CO emissions and transport during the summer/winter monsoon over the Indian subcontinent using long-term satellite data. Detailed analysis of data from 16 flights with the CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container, https://www.caribic-atmospheric.com) aircraft between Frankfurt and Chennai, India have been carried out during a short period from April to December 2008 (Schuck et al., 2010). An enhancement of CH4 mixing ratios and elevated levels of N2O and CO were observed throughout the monsoon seasons south of 40°N at the altitudes between 8 and 12.5 km over the Indian continent.

The IGP is also polluted by the long-range transport of air mass from the western countries. Sometimes the source of the pollutants is local from the Thar Desert located in the western parts of India and from the Arabian Peninsula over the land through Afghanistan and Pakistan, sometimes the airmass enters the western parts of India crossing over the Arabian Sea from the Arabia Peninsula (Prasad and Singh, 2007a; Singh et al., 2008). The pollutants in the IGP, depending on the meteorological parameters (wind direction and speed, relative humidity, air temperatures), reach up to the eastern parts of the IGP and further reach over Bangladesh and the central parts of India (Dey et al., 2004; Singh et al., 2004; Prasad and Singh, 2007a; Aloysius et al., 2008; Sarkar et al., 2019; Chauhan and Singh, 2020; Singh and Chauhan, 2020; Chauhan et al., 2020). The pollutant outflow from the IGP reach over the neighboring country Bangladesh and beyond over the northeastern state, Assam, and the Bay of Bengal; the intensity and the extent depend on the meteorological conditions which in turn depend on season.

Understanding the dynamic behavior of atmospheric aerosols over the IGP is a great challenge since numerous parameters control the dynamics of aerosols. The ground observation of aerosol optical parameters is almost nonexistent prior to January 2001. In January 2001, under a joint collaboration between IIT (Indian Institute of Technology) Kanpur and NASA, a ground based AERONET station was established and AOD parameters were made available to scientists (Singh et al., 2004). The AERONET provides quality data, which was freely used by Indian and international scientists, which have helped the scientific community to understand the aerosol properties, radiative budget, dynamics of pollution, fog formation, long-range transport of dust, and outflow of the pollutants from IGP.

2: Brick kilns

In many of the Asian countries, including India, China, Pakistan, Nepal, and Bangladesh, buildings are built with bricks. The brick molds are made using alluvial soils and are baked in coal-fired brick kilns, such brick kilns are densely located in the IGP. The Indian coals are of poor quality and their use causes intense emissions of CO2. The emissions are dispersed in the local area due to low height of chimney and such brick kilns are located closely, sometimes five kilns are found within 2 km radius. These brick kilns emit huge amount of black carbon (BC) (UNEP, 2011; Arif et al., 2018a). The CO2 emissions from brick kilns are a threat to local people and have long-term impacts on climate change from local to regional levels. Fig. 8 shows the emission of black plume from dense brick kilns in the IGP. Brick kilns are also known as the source of SO2 emissions, and the amount is estimated to increase many folds by 2040 than what was found in 2015 due to the growing use of coal in brick kilns (Arif et al., 2018a).

Fig. 8

Fig. 8 (A) Brick kilns located in the northern parts of India, along the Varanasi—Singrauli road. The black plumes from closely spaced brick kilns, which are one of the sources of atmospheric pollution. The smoke plume directly poses threat to people living close to these brick kilns. (B) Pile of heated dust bricks is placed just in front of the brick kiln. Panels (A) and (B): Photo taken by Ramesh Singh.

3: Coal-based thermal power plants

In India and China, coal-based thermal power plants are the major sources for electric power generation. A dense network of power plants in China and India is shown in Fig. 9A and B. Prasad et al. (2006a) using satellite data found high aerosol optical depth over these power plants which are considered as one of the major sources of atmospheric pollution. These power plants are also the source of very high concentrations of black carbon and NO2 (Prasad et al., 2012; Singh et al., 2018; Kumar, 2021).

Fig. 9

Fig. 9 (A) Distribution of a total of 1959 coal-fired power plants in India. Of these, some plants are closed, some are operational, and some are under construction. (B) Location of a total of 5416 coal-fired thermal power plants in China, including closed, operational, and new proposed locations. Panel (A): https://endcoal.org/tracker/, accessed on December 26, 2020. Panel (B): https://endcoal.org/tracker/, accessed on December 26, 2020.

Thermal power plants are also the major source of NO2 and SO2 and other gases (Prasad et al., 2006a, 2012; Singh et al., 2018; Romana et al., 2020). Singh et al. (2018) observed elevated concentrations of black carbon in and around coal-based power plants in Singrauli areas. Arif et al. (2018b, 2020) found high indoor concentrations of black carbon in the eastern parts of the IGP where coal mining activities are very high. China has coal-based power plants of capacity 1,022,877 MW, whereas India has about 1.44 times lower capacity (228,157 MW) coal-based power plants. China and India are the major populated countries in Asia. Both countries are known to be highly atmospheric polluted countries in the world especially Beijing and New Delhi, capitals of China and India, respectively (Zheng et al., 2017). The rapid urbanization and industrialization led to a rise in air pollution in recent years (Guo et al., 2011; He et al., 2019; Zhao et al., 2019). China has been suffering from serious air pollution which is the main cause of dense haze and fog in China (Luo et al., 2018; Tong et al., 2018a,b) during winter season. In the past two decades, such dense haze and fog were very common; late running and cancellation of flights were common due to poor visibility.

In recent years, after 2011, China made efforts to cut down atmospheric pollution by closing and shifting some of the industries from Beijing, consequently the atmospheric pollution reduced in China (Li et al., 2020). These efforts have been made by the Chinese Government due to adverse effects of air pollution on human health and daily life. Chinese government has implemented continuous emission control measures. Since 2011, the anthropogenic emission sources and their amount in China have undergone dramatic changes due to both the rapid transition of economic structures and environmental policies (Li et al., 2019, 2020). The coal-based power plants appear as hot spots for NOx emissions in satellite images (Fig. 1 of NOx, Chapter authored by Vinod Kumar, in this book). Singrauli area is hot spot for NOx emission where several coal power plants (Fig. 10A) are located (Prasad et al., 2006a). The BC emissions and ground measurement of aerosol optical depth were found to be elevated compared to the surrounding areas, coal mines (Fig. 10B) exist in the proximity of power plants. The ground measurements of AOD and black carbon (BC) measurements were carried out in the Singrauli area (Sarvan Kumar took the measurements of AOD using Microtops sun photometer instrument). The coal is used in these power plants. The emissions are from power plants and coal mining activities; the Singrauli area is one of the highly polluted areas (Singh et al., 2018) (Fig. 10B).

Fig. 10

Fig. 10 (A) Sarvan Kumar taking measurements using Microtops sun photometer close to coal-based power plants in Singrauli area. (B) The image of atmospheric pollution from Singrauli coal mining area. (C) Locality of poor people close to coal-based power plants in Singrauli. (D) The poor people use free coal for cooking purposes. The burning of coal is polluting the surroundings and within such an intense smoke people live in this area. Panels (A) and (B): Photo taken by Ramesh Singh.

During winter season, the Singrauli area appears to be covered with smoke and BC and thick smoke/fog can be seen (Fig. 10B). High atmospheric pollution and BC emissions from coal power plants and dust emissions are clearly apparent. The green vegetations, mud houses, and vehicles are covered by thick layer of fly ash and road dusts. The vegetation cover in the surrounding areas of the power plants is impacted. The emissions from power plants are the source of acid rain. Not much information is available about the acid rain, detailed measurements, chemical analysis, and impact studies will provide a better understanding of the short- and long-term changes associated with the power plant emissions. Fig. 10C shows locality of poor people covered by layers of fly ash and road dusts. People living in such a highly polluted environment (Fig. 10D) suffer from all kinds of diseases.

4: IOC fire of October 29, 2009

Accidental and natural fires due to unknown reasons are common and sometimes it becomes difficult to control such fires and takes 1 or 2 days. A huge fire occurred at Indian Oil Corporation (IOC) (Fig. 11A) located at Sitapur near Jaipur city on October 29, 2009 around 6:00 p.m. High flames up to 70 m were seen and emission of black plumes were observed over the next few days.

Fig. 11Fig. 11Fig. 11

Fig. 11 (A) Photo of Jaipur IOC fire. (B) Terra satellite image of October 30, 2009. The inset image shows dispersion of heavy plume in southeast direction. The plume continued for 2 days. (C) Higher value of TOMS-derived aerosol index and ozone column compared to the average value of AI and ozone column for the months January to May during 1979–93. Panel (A): Photo taken on October 29, 2009. Panel (B): https://worldview.earthdata.nasa.gov/. Panel (C): Plot generated by A.K. Prasad using TOMS AI and Ozone Column Data.

The huge fire killed few and injured a dozen of people. Soon after this huge fire, people living in the adjoining areas escaped and a spurt of patients complaining respiratory problems were reported, who were taken to the nearest hospital for medical care. The people living in the surrounding villages suffered eye irritation and rashes and were also rushed to the nearest hospital for emergency care. Huge amount of carbon soot was seen in the atmosphere, which was deposited in the field and houses. Huge emission of toxic gases such as CO, CO2, SO2, NOx was due to the burning of oil; these gases modify the atmospheric composition initially over the IOC region and with time dispersed in the direction of wind toward southeastern parts affecting major cities (Kota, Gwalior, etc.) (Fig. 11B). Soon after the fire, cloudy conditions were observed over Delhi, which is northeast of IOC, with a thick smog, which interrupted road and air traffic for a couple of days. Detailed analysis of multisatellite data (MODIS, AIRS, OMI AURA, AMSER) were carried out. Terra MODIS image (1 km and 250 m resolution) clearly shows the dispersion of plume. The plume dispersed in the southeast direction due to the dominance of northwesterly wind in the region. Numerous atmospheric (aerosol optical depth, angstrom coefficient, water vapor and CO mixing ratio, total ozone column) and meteorological parameters (air temperature, relative humidity) were changed associated with this fire. The AIRS data show increase in the concentrations of carbon monoxide and changes in atmospheric parameters around 500 hPa pressure level in the nearby cities due to winds in the southeastern areas affecting major cities such as Kota, Gwalior, etc., located in downwind sides.

It has also been found that after the fire the temperature increased significantly near Jaipur and reached to a maximum of 44°C. Even the adjoining regions such as Agra, Delhi, and Kota also suffered due to rise in the temperature. The suspended particles in the air, which are responsible for health problems, did not move away due to steady air movement, and in turn affected many people who are prone to allergy, asthma, and heart decease. On November 6, 2009, Delhi was badly affected by fog and visibility reduced to 500 m. Scientists have claimed that the thick fog layer is due to suspended particles and the IOC fire may be an important reason for such unusual fog layers. People living in the areas complained about eye irritation on November 6, 2009. During 10 days of fire, huge amount of sulfur oxide suffused in the air along with several other lethal gases within a 10–20 km radius. Such accidental fires occur in different parts of India, which have short-term impacts. Like these fires, crop residue burning is common in the western parts of India and the impacts are visible over some of the major cities in IGP. A detailed discussion on crop residue burning is included in this chapter.

The long-range transport of smoke was observed over the Himalayan foothill region in 1991. A huge oil well fire in Kuwait occurred in February 1991. Thick dark smoke clouds associated with this burning oil well have been seen in data from weather satellite METEOSAT (Limaye et al., 1991). The thick smoke plume dispersed over a wide area and further the plume even reached the Himalayan foothills. Due to the long-range transport of smoke plume, the aerosol index was observed to be higher than the average value of January to May 1979–93. Similarly, the total ozone column also enhanced due to smoke plume compared to the average ozone column value for the months January to May during 1979–93 (Fig. 11C).

5: Forest fires in the Himalayan region

All along the Himalayan region, thick forests are located, these forests suffer from fires due to strong wind, dry conditions, heat waves, and strong lightning especially when the vegetations are dry (Vadrevu, 2012). Forest fires are caused by both natural (dry seasons and lightning) and human-induced (burning of forest for crop) causes. The uneven distribution of the rainfall and dry weather conditions are the major causes of rise in forest fire episodes. The dense forest in the Himalayan region, dry vegetation, and favorable meteorological conditions (relative humidity, air temperature, and wind speed) during the summer season are the causes of forest fires that severely affect the air quality (Chand et al., 2007; Kumar et al., 2019). Sometimes people living in the mountain areas burn surrounding vegetations to regenerate green vegetation to use as fodder for animals. In some cases, such small fires spread in the area and the surrounding areas are covered with thick smoke and clouds. Depending on the wind direction, the smoke spreads over the foothill areas affecting the air quality.

Sometimes forest fires are very wild and continue for a week or two due to poor logistics (facilities, roads and due to hilly terrains).

The forest fires cause atmospheric pollution. In recent years, increase in the frequency of the forest fire episodes has been observed globally. The 2020 California and Australian forest fires and the 2021 Nagaland Forest Fire and Odisha forest Fire of India are some of the important forest fires. Forest fires are responsible for the emission of 3.33 Tkg of carbon per year and 8 Bkg of nitrogen emission per year (Van-der Werf et al., 2004).

A case of forest fire which occurred on April 12–15, 2016 can be clearly seen in MODIS true color image (Fig. 12), which shows smoke from the forest fire along the Himalayan foothill region. The smoke plume is dispersed toward the higher altitude in the Himalayan region and to the northeastern parts of India. The red and blue lines show the 48-h forward trajectory obtained using HYSPLIT trajectory model. The red dots show the MODIS fire and thermal anomaly. In India, forest fires occur mostly in the western Himalayan region due to human activities, such as cultivation in forest, trekking, camping, lightning, cooking, and other carelessness. Forest fires are responsible for the large-scale emission of various gases such as CO2, CO, CH4, H2, CH3Cl, NO, HCN, CH3CN, COS, and atmospheric aerosols (Crutzen et al., 1979). The natural forest fires are important for the ecosystem of the forest but depending on the meteorological conditions, the fire can be unmanageable and can devastate the whole ecosystem (Yell, 2010; Moritz et al., 2014; Alexandre et al., 2015). Uncontrolled large-scale and intense forest fires can make noteworthy impacts over a large region (Salis et al., 2014). Large fires also affect a large population residing close to the landscape damaged by it (Vitousek et al., 1997; Weng, 2007; Hendrychová and Kabrna, 2016). Mega fires can change the local climate for short and long terms. Depending on the scale of the fire, ecosystem, nutrient cycles, the rate and amount of gas emissions and PM concentrations (Chuvieco and Martin, 1994; Tansey et al., 2002; Adams, 2013; Hurteau et al., 2014; Rocca et al., 2014) are impacted. The large- and mega-scale forest fires have various effects from loss of human life to damage to property, and changes in fundamental characteristics to loss of the whole ecosystem (Yell, 2010; Moritz et al., 2014; Newman et al., 2014). The change in land cover due to fires can be more critical if it reaches the urban area or densely populated region (Adams, 2013; Moritz et al., 2014).

Fig. 12

Fig. 12 MODIS true color image taken on April 12–15, 2016 showing smoke from the forest fire in the Himalayan foothill region. The smoke plume can be clearly seen which has dispersed toward the higher altitudes in the Himalayan region and to northeastern parts of India. The red and blue lines show the 48-h forward trajectory obtained using HYSPLIT model. The red dots show the MODIS fire and thermal anomaly.

6: Air pollution associated with civil aviation

With the growing industrialization and economic developments all over the world, the civil aviation industries have grown. In Asian countries, including India, number of flight routes has grown in the last two decades and major cities have been connected through domestic flights. India is connected with different countries through international flights. A number of airplane companies are covering flight routes connecting major cities in different countries in different continents. The air jets routes can be seen in the sky especially during winter season, it is easy to see the jet routes, and one can see contrails. Soon after the flight passes, narrow contrails spread, showing wider contrails depending on the meteorological conditions. The airplanes fly at an altitude of 10–11 km, the airplanes take off and land at the airport. The emissions from large airplanes are higher than that from smaller airplanes. The MOZAIC program was initiated in 1993 by European scientists, aircraft manufactures, and commercial airlines to understand anthropogenic and air traffic emissions and their impact on the atmosphere. Efforts were made since 1993 to carry out continuous and automated measurements of temperature, pressure, wind, relative humidity, water vapor mixing ratio, and ozone from these aircrafts (Airbus A340 aircraft) along five long-range aircraft routes (Marenco et al., 1998). All these sensors are deployed onboard airplanes and operate continuously from taking off from the airport to landing at the airport. O3 is measured with a modified commercial dual beam UV-absorption photometer. The overall uncertainty is estimated to be about ± 2 ppbv + 2% of the observed reading, which corresponds to ± 2 ppbv for 10 ppbv O3 mixing ratio and ± 4 ppbv for 100 ppbv O3 mixing ratio (Thouret et al., 1998). Temperature is measured with a platinum sensor with an estimated uncertainty of + 0.01°C (Helten et al., 1998). MOZAIC measures relative humidity (RH) with respect to liquid water with compact airborne humidity sensing devices (Helten et al., 1998). In the middle troposphere, the overall uncertainty lies within ± 4% RH and around ± 7% RH between 9 and 13 km. Beginning of 2001, regular measurements of CO and nitrogen oxide (NOx) were also added into this program (Nedelec et al., 2003). The CO instrument has a 30-s response time (300-m vertical resolution) and an accuracy of about ± 5ppbv (± 5%) (Nedelec et al., 2003). MOZAIC observations are available since mid-1994 and cover large parts of Europe, North America, and East Asia; the measurements of each flight are divided into three sets: ascent, cruise, and descent.

Sahu et al. (2009) used MOZAIC aircraft data for the period 1996–2001 over Delhi and have observed strong seasonal variations in tropospheric ozone (TO) and water vapor. However, considerable uncertainties remain in the vertical characteristics of O3, CO, NOx, HC, CH4 over IGP. The close relationship between the source-sinks of the pollutants (O3 and CO) and effects of meteorology in the mixing ratios are important to understand the detailed characteristics and dynamics. Simultaneous measurements of O3, water vapor, and CO vertical profiles over Delhi are analyzed using aircraft Measurements of Ozone and Water Vapor by Airbus In-service Aircraft (MOZAIC) program (http://mozaic.aero.obs-mip.fr). They have also compared MOZAIC measurements of CO vertical mixing ratios from MOPITT (Measurements of Pollution in the Troposphere) with AIRS (Atmospheric Infrared Sounder) data. Coupled Model Intercomparison Project Phase 5 (CMIP5) model simulations are also evaluated against MOZAIC measured O3 profiles in different seasons. The role of meteorology in the distribution of O3 and CO over Delhi has also been investigated using long-term reanalysis data over India.

Bhattacharjee et al. (2015) analyzed more than 300 MOZAIC aircraft vertical profiles (combining individual ascending and descending flights) over Delhi during the period 2003–06. Number of profiles (combining ascending and descending flights) were highest in the month of September (45 in total), followed by the month of June (36) and the month of October (30), the number of profiles were lowest during the month of April (8 in total), December (18), and November (19) during the period 2003–06. CO data are available for 65% of the total ascending profiles and 81% of the total descending profiles. Both ascending and descending profiles have measurements at the pressure levels 980 to about 220 mb at narrow regular pressure intervals (12–15 mb). Since the profile data intervals are frequent, each of the daily measurements was averaged at 50 mb equal intervals (at an altitude equivalent to the pressure level 1000–200 mb). From these data, they examined monthly and seasonal vertical variations of various parameters for both ascending and descending flights.

Vertical distributions of O3, CO, and H2O mixing ratios for both ascending and descending flights at Delhi international airport were investigated. O3 mixing ratio was found to be highest during premonsoon season (March-April-May: MAM) at the pressure levels 900–450 mb (between boundary layer and mid-troposphere) compared to all other seasons. During premonsoon season, meteorological conditions over Delhi were generally higher sunlight (~ 250 h per month), warm temperature (37–40°C), and low humidity (~ 30%); these conditions favor the formation of tropospheric O3 through photolysis reactions. During premonsoon season higher value of CO was observed, which shows that higher mixing ratio of precursors and favorable meteorological conditions both contribute to higher production of O3. At the time of onset of monsoon (beginning from the end of July), moisture in the atmosphere is higher (Singh et al., 2004; Prasad and Singh, 2007a, 2007b, 2009; Kumar et al., 2013); O3 is destroyed by OH radical and washed out of the atmosphere. O3 is low during monsoon season compared to premonsoon (MAM) because of low sunlight availability (~ 217 h per month) and lower temperature (~ 20°C). During winter season, the atmospheric conditions are stable over Delhi below the boundary layer which restricts mixing near surface air and provide higher concentration of ground level pollutants. Bhattacharjee et al. (2015) have carried out detailed studies about the dynamics of vertical profiles of O3 over Delhi. During premonsoon season (MAM), ozone concentration over Delhi was higher at the pressure levels 900–400 mb than the postmonsoon (ON) and winter season (DJF) concentrations at the same altitude. At the pressure levels 900–400 mb, O3 varies in the range 55–57 ppbv during premonsoon season (MAM), 47–50 ppbv during winter season (DJF), and 52–53 ppbv during postmonsoon season (ON). O3 increases from 55–57 ppbv (below 400 mb) to around 80 ppbv during premonsoon season (MAM) in the upper troposphere (at pressure levels 200–400 mb). An enhancement of O3 was observed in both ascending and descending flights from MOZAIC data, the findings of Bhattacharjee et al. (2015) was also obtained from aircraft, balloon, and satellite observations (Gupta et al., 2007; Sahu et al., 2009; Fadnavis et al., 2010, 2011; Ganguly and Tzanis, 2011) over Delhi and northern parts of India during winter-premonsoon season. The enhancement of ozone in the upper troposphere was likely due to the stratospheric influence/stratosphere-troposphere exchange