The planet has supported the production of ample oxygen and combustion fires since the time of adequate vegetation. Fire regimes are highly influenced by ecosystem composition, viz., fire frequency, spatial continuity, size, seasonality, types of fire (surface or ground fire, crown fire), fire severity, and intensity [16,17]. Industrial combustion, domestic combustion, societal combustion, agricultural combustion, and support services are the significant influencers of combustion due to human involvement with some risks and benefits [18]. The most tenacious combustion occurrence is smoldering combustion, as it is the most destructive fire process, which is a slow and low-temperature activity and a flameless burning process. Smoldering combustion is emerging as an industrial and environmental challenge; smoldering fires are a rising concern globally. During the smoldering process, sometimes, the flames’ disappearance follows a greater extension, devouring amounts of fuel and liberating toxic gases in the environment. Sturdy buoyant forces are involved in these kinds of fires, where firebrands initiated by bark and twigs are elevated and carried long distances (hundreds of meters) by the wind in downward directions, igniting several fire scenes [19]. There are research gaps in smoldering combustion, which can also be a beneficiary process for human beings. To have detailed knowledge, one can make use of recent reviews [20,21,22,23,24]. Globally 26–29% of forest loss is because of forest fires during the 2001–2019 period, which is higher compared to the 2001–2015 (21–25%) and 2003–2014 (12–18%) periods. Due to fire incidents, boreal forests have a high segment of forest loss (69–73%), following subtropical (19–22%), temperate (17–21%), tropical (6–9%), and rainforests (7–9%). Australia has an increasing trend in forest loss in the tropical, subtropical, and temperate areas, and in Eurasia, boreal forests demonstrate a high loss proportion [25,26,27]. In India, about 52,785 and 345,989 forest fires were analyzed from Nov 2020 to June 2021, i.e., the forest fire period, using a moderate resolution imaging spectroradiometer sensor and Suomi National Polar Orbiting Partnership Visible Infrared Imaging Radiometer suite. In Indian forests throughout the fire season, 54.4% see occasional fire, with 7.49% moderately frequent fires and 2.40% high incidence levels, and 35.71% remains non-exposed [28]. Recent fire events in Brazil, Australia, and California have again drawn full attention towards forest fires, chiefly the Amazonian fires, where whether forests or deforested areas were burning was not clear [29,30]. On the other hand, the waste and recycling industry is on the verge of providing energy, recycling, sorting, and yielding waste fires, which is an epidemic, as reviewed by Fogelman (2018). Germany, the UK, Sweden, Austria, and Italy are some of the major countries in Europe with the most incidents of waste fires [31,32]. However, major health risks were also observed with the waste fire incidents that have occurred in the cities of the USA and Thailand [33,34]. Stubble burning is the major contributor of air pollution by emissions of CH₄ SO_x, PM of 10 (PM₁₀) and 2.5 (PM_2.5) microns, nitrogen oxides (NO_x), CO₂, and CO in mostly South Asian countries such as India, Nepal, Bangladesh, and Pakistan and also in China (Figure 1). Globally, around one-fourth of biomass burning activities (household cooking, countryside communal refuse ignition, wildfires) are constituted by stubble burning regimes including forest fires comprehensively [35]. Due to changes in patterns of cropping and harvesting and water scarcity, agricultural fires are increasing in India [36]. Despite various interventions and the banning of these crop residue burning practices, this burning regime is still extensive. It has engendered about 44,000–98,000 deaths in 2003–2019, with the exposure of PM substances in the atmosphere where Haryana, Punjab, and Uttar Pradesh are the major contributors (Figure 2). India has a rich diversity of crops including rice, wheat, coarse cereals, pulses, oil seeds, sugarcane, cotton, jute and mesta, but rice and wheat, being rich producers, have a more diversified impact as their residues are burnt in large amounts for cropping processes. Sugarcane’s residues are also burnt in large amounts in India. About 6600 Mt of these crops residue were burnt during 2003–2016 [37]. There is a literature gap in studies of stubble burning and Diwali fireworks as these two events coincide with each other in India. Thus, the effect of the festival fireworks is somehow the same; stubble burning as SO₂ and PM_2.5 (900 μg/m³) are the major pollutants emitted during the fireworks process [38]. Combustion effluents are generated in response to the behavior of the burning process and product toxicity, which further resides in the fire plot (orientation and fuel’s shape), material composition, oxygen concentration, and temperature. These combustion effluents are gases, vapors, and liquids, and solid particles mix in varying ratios of combustion conditions to the material’s organic and elemental composition [39]. The effluents produced in the environment after burning the products are irritable and asphyxiant to humans. Asphyxiate gases, irritable gases, and complex molecules are some significant types of combustion effluents (Figure 3).

Combustion, on the one hand, is full of risks and, on the other hand, is equally responsible for a number of benefits. The combustion process involves generating energy, heat, light, chemical species, mechanical work, and plasma. During the reaction between diesel fuel, hydrocarbons, oxygen, carbon dioxide, and water are produced, resulting in combustion. This conversion of diesel fuel to energy is obligatory for power buses; further, it also helps in exhausting the greenhouse gases responsible for climatic change and toxic air pollutants which smudge the atmosphere [40]. A total of 25% of the world’s power is provided by internal combustion engines (ICE), which are operated by fossil fuel oils. ICEs are enhanced by the conversion of catalysis beneficial to uniting emission standards with a coating of a metal catalyst to ceramic structure in order to reduce pollutants and intensify combustion. ICEs are still the transportation industry’s future, so there should be future efforts to reduce greenhouse gas emissions in the environment, which will be discussed in the coming sections [41]. Hydrogen-fueled (HF) ICE (HF-ICE) can be a potent approach for ecological road mobility elucidations, which will also meet the neutrality objective of the EU’s 2050 CO₂. These HF-ICE are advantageous over diesel engines in automobile industries as they have virtually no emissions and lofty efficiency. So, HF-ICE should be taken into consideration, noting both its advantages and its limitations [42]. Rice husk combustion (1 tonne/h) can boost an average net of 600–700 KWh electricity for any power plant with less NOx and CO effluent emission (below 250 ppm). Moreover, rice husk ash can recover bio-silica of 99.7% purity. So, rice husk combustion can be utilized for energy development [43]. Coal is the ally of the world for electricity production compared to other sources, producing 40% of the world’s supply. Abundance, affordability, standard technology, reliability, efficiency, and safety are the key benefits of coal-fired power plants [44]. The year 2021 has seen increased energy generation by coal-fired power plants by 8%, which has technically reversed the decline over the past two years. European Union (20%) > United States (16%) > India (13%) is the increasing demand trend for coal-fired stations [45].

Incorporating agricultural stalks (decomposition) into the soil can increase its fertility and level of nutrients, organic matter, microbial activity, and water-holding capacity. Bio-decomposition and vermicomposting are some of the decomposition techniques for crop residue management that are helpful in the generation of bio-compost and bio-fertilizers, respectively, which can be further used in agricultural practices. Biochar production by the conversion of biomass by thermal combustion can be used for reducing carbon footprints during rice production [46]. Crop residue waste can be used to produce biogas, bio-hydrogen, and bioethanol; 12 TWh of electricity can be generated in biomass power plants with crop residue usage [47]. In Iran, a study evaluated that 2082 Mm³ (hydrogen), 6542 Mm³ (biogas), and 2443 M liter (butanol) could be yielded by 24.3 Mt of crop residue [48]. Crop residues can be used for bioenergy production and thus will be helpful for waste and air pollution management.

During the combustion of various materials, many effluents are dispersed in the environment, which can have an affect depending on the exposure duration, receptor susceptibility, and transmission process. These combustion effluents consist of solid gases, vapors, and liquid droplets with a particular size range. After cooling fire effluents, a chemical composition still exists where vapors form in submicron fields by condensation into liquid droplets and solid particles. Inhalation hazards during a fire by the occupants in remote areas are prevented when acid gases, organic particulates, and vapors are retained on building surfaces and elevated after fire risks [49]. The effluents are emitted into the air, water, and terrestrial environments. PAHs, hydrocarbons, VOCs, metals, dioxins, suspended solids, and ammonia are key concerning effluents produced during the firing process [50]. Burning stubble, such as sugarcane, can accumulate mercury in the soil and streams. Mercury can be toxic to humans and wildlife and cause developmental problems in fetuses. Stubble burning is the source of major gaseous pollutants, i.e., GHGS, NOx, SOx, and PM (PM₁₀ and PM_2.5), causing major human and environmental health issues. Approximately 63 Mt of crop stubble can emit CO (3.4 Mt), CO₂ (91 Mt), CH₄ (0.6 Mt), NOx (0.1 Mt), and PM (1.2 Mt) into the environment [4]. A recent study likely reported CO₂ (176 teragrams (Tg)), CO (10 Tg), CH₄ (314 gigagrams (Gg)), N₂O (8.1 Gg), NH₃ (151 Gg), non-methane volatile organic compounds (NMVOC, 814 Gg), PM_2.5 (453 Gg), and PM₁₀ (936 Gg) emissions from crop residue burning in northwestern India [51]. These stubble burning pollutants are transported from the Indian Punjab region to Pakistan, and vice versa. According to the air’s trajectory analysis, it was found that with compact bumps from the adjacent countries, transnational dispersal of pollutants exists across Bangladesh, India, Pakistan, and Nepal [52,53]. According to the world bank data, USD 8.1 trillion yearly is the cost of health damages originating by air pollution, which corresponds to 6.1% of the gross domestic product (GDP) globally [54]. In India, USD 28·8 billion of economic losses were recorded in 2019, and this cumulative deprivation of USD 36·8 billion was 1.36% of India’s GDP [55].