Air Pollution in Japan and the World

Abstract

This chapter explores air pollution issues in Japan and the world. It reviews pollution problems caused by air pollutants such as sulfur dioxide (SO₂) and suspended particulate matter (SPM). The chapter also discusses Japanese air pollution policy measures, including sulfur charges and vehicle type regulations, from an economic perspective. The discussion then moves to air pollution in the world. Household air pollution in developing economies and related issues are discussed in the broader context of SDGs.

1 Introduction

Since the coronavirus pandemic began in 2020, so many lives have been lost and economic activities were severely affected by the large-scale restrictions such as lockdowns and travel bans. Meanwhile, these measures brought some positive impacts on the environment. The U.S. EPA AirData shows that the air quality in Los Angeles was the cleanest in decades during the pandemic’s first year (CNN, April 7, 2020¹). Likewise, the level of air pollutants in Southeast Asia decreased by 40%, according to the World Meteorological Organization (UN News, September 3, 2021²). The improvement in air quality was dramatic but might be short-lived. Air pollution remains a serious problem especially in non-OECD developing economies. According to the OECD estimates (2014), the economic costs of health damage by air pollution in China and India are $1.4 trillion and $0.5 trillion, respectively, and these combined costs are greater than those of all OECD countries ($1.7 trillion).

The OECD’s estimates, updated in 2016, indicate that the world’s economic losses from air pollution would increase to $18–25 trillion by 2060. The welfare losses from premature deaths caused by air pollution are estimated to be about $3.4–3.5 trillion by 2060 in the OECD countries, a sharp rise from $1.4 trillion in 2015, and an even greater number of losses is expected in non-OECD countries. Air pollution has been serious especially in non-OECD Asia over the last ten years. Beijing is known as a city with one of the highest levels of air pollution mainly due to coal combustion that causes PM_2.5 emissions. High concentrations of PM_2.5 have been observed in Seoul as well. Mumbai and Delhi are among the top list of cities with the worst air quality. The air in Ulaanbaatar, the capital of Mongolia, is severely polluted in winter due to the burning of coal for heat at home.

Polluted air caused environmental and health risks also in Japan during its rapid economic growth in the 1960s and 1970s (see Chap. 2 for details). The pollution levels started to drop significantly after regulatory policies were implemented in the mid-1970s. Presuming that Japan’s experience of overcoming the problem serves as a reference for developing countries facing air pollution, we will review some of the key policies and regulatory standards adopted by the Japanese government. In the following section, we will provide background information about air pollution by identifying its sources, causes, and health effects. We will then review air pollution problems in Japan and discuss the nation’s countermeasures and the extent to which they contributed to improving the air quality. Finally, we will turn to the current situations in non-OECD countries, especially in Asia where air pollution is a serious concern both in outdoor and indoor environments.

2 Sources, Causes, and Health Effects of Air Pollution

Air pollution is primarily caused by the combustion of fossil fuels (e.g., coal, oil, and natural gas) that contain sulfur. When these fuels are burned, sulfur is oxidized to form sulfur dioxide (SO₂), one of the primary air pollutants that causes health problems such as bronchitis and asthma. Fossil fuel combustion also produces nitrogen oxides (NOx), another primary air pollutant, which is formed by the oxidation of nitrogen in the fuels. NOx is generated also when automobile engines and boilers in factories are heated, causing nitrogen and oxygen in the air to combine. Usually existing in the air as nitrogen monoxide and nitrogen dioxide, NOx causes harmful effects on lungs. It reacts with organic compounds emitted from factories and automobiles in the presence of ultraviolet light (UV) in sunlight and forms photochemical oxidants. They cause photochemical smog that results in health hazards such as headaches, breathing difficulties, and painful irritation of the eyes and throat.

SPM, VOCs, and PM_2.5 also cause air pollution and respiratory diseases. SPM, or suspended particulate matter, is particulate pollution suspended in the air whose size is 0.01 mm or less. It comes from a wide variety of sources, including soot from fuel burning in factories and natural sources such as yellow dust from China. Volatile organic compounds (VOCs), such as xylene, toluene, and ethyl acetate, are a general term for organic compounds that are volatile and become gaseous in the atmosphere. VOCs produce SPM and photochemical oxidants, which are, again, major causes of air pollution and health effects. Sources of VOCs emissions include automobile exhaust gases and the evaporation of fuels, solvents, and paints from factories. PM_2.5 refers to fine particles whose diameters are 2.5 μm or smaller. Soot, dust, and sulfur oxides generated in factories are the major causes of the particles.

These harmful pollutants were widespread in Japan when heavy chemical industry played the leading role in industrialization. SO₂ caused the Yokkaichi asthma outbreak, one of the major pollution diseases that occurred in the 1960s.³ Photochemical smog was formed frequently in the 1970s, especially in the Kanto⁴ and Kinki⁵ regions. Although the occurrences of smog have decreased at present, the problem has not been resolved completely; photochemical smog alerts were issued as recent as in 2021. SPM and PM_2.5 blowing in from China have still been observed widely across Japan, triggering some concerns for allergies and respiratory problems.

3 Air Pollution and Policy Measures in Japan

Given its impact on the environment and public health, air pollution is listed first of the seven major types of pollution in the Basic Environmental Law that serves as the national guidelines for formulating environmental policies in Japan. Air pollution severely affected the lives of Japanese residents, especially those who lived in industrial areas or near streets with heavy traffic. Residents of Yokkaichi suffered from respiratory ailments such as chronic bronchitis, bronchial asthma, and pulmonary emphysema due to the burning of petroleum and crude oil at oil refineries and petrochemical factories. The polluted air throughout Japan led to numerous civil lawsuits against firms by victims seeking compensation from the polluter for damages that exceed the “tolerable limit.” (ERCA 1997).

The victim’s transaction costs (i.e., costs associated with bargaining with the polluter)⁶ were significant back then because the civil law stipulated that the obligation to pay compensation for damage arises only when the polluter was found to have been intentional or negligent. That is, compensation would not be paid to the victim unless it was proven that his or her health damage was caused by the polluter’s willful misconduct or negligence. Many victims still opted to file lawsuits. In response to an ever-increasing number of pollution victims and lawsuits, the government enacted the Pollution-Related Health Damage Compensation Law in 1973 as a relief measure for the victims. Consequently, transaction costs of the victims were significantly lowered as they no longer had to prove the polluter’s misconduct or negligence.

With the aim to implement countermeasures effectively and comprehensively, the government also established the Environmental Agency, which is the former body of the Ministry of the Environment (MOE) in 1971. Air quality standards were introduced subsequently in 1973 and thereafter. For example, standards for SO₂ concentrations were set that the daily average for hourly values shall not exceed 0.04 ppm, and the hourly value must be 0.1 ppm or less.

Figure 8.1 shows fluctuations in SO₂ concentrations in Japan from 1972 to 2017. SO₂ concentrations have been measured and monitored by the MOE at two types of stations: general ambient air monitoring stations (hereafter called “general stations”), indicated in the figure by the dashed line, and roadside air pollution monitoring stations (hereafter called “roadside stations”), represented in the figure by the solid line. General stations are installed in residential areas to monitor general air quality. Roadside stations are installed at intersections and nearby major roads to measure the level of pollution caused by vehicle emissions. As shown in the figure, the SO₂ levels dropped after the standards were introduced in 1973 and then significantly improved by the 1990s.

Fig. 8.1

Source MOE “FY2019 Environmental Health Surveillance for Air Pollution,” adopted by the authors

SO₂ concentrations in Japan.

Subsequently, the standards for NO₂ were introduced in 1978, limiting the daily average for hourly values to be within or below the 0.04–0.06 ppm zone. Figure 8.2 shows fluctuations in NO₂ concentrations in Japan from 1970 to 2015. Just like SO₂, NO₂ levels are measured at general stations (represented in the figure by the dashed line) and roadside stations (represented by the solid line). Unlike what we observed for SO₂ in Fig. 8.1, NO₂ concentrations did not improve dramatically, and they remained relatively high even in the 1990s. We will come back to discuss this point further later in this chapter.

Fig. 8.2

Source MOE “FY2019 Environmental Health Surveillance for Air Pollution,” adopted by the authors

NO₂ concentrations in Japan.

Standards were also introduced for photochemical oxidants and SPM in 1973. Hourly values of photochemical oxidants shall not exceed 0.06 ppm. With regard to SPM, the daily average for hourly values shall not exceed 0.10 mg/m³ and hourly values shall not exceed 0.20 mg/m³. Much later in 2009, standards were adopted for PM_2.5: the annual standard is less than or equal to 15.0 μg/m³, and the 24-h standard (i.e., the annual 98th percentile values at designated monitoring sites) shall be less than or equal to 35 μg/m³.

Figure 8.3 shows fluctuations in SPM and PM_2.5 concentrations from 1974 to 2019. Similar to what we observe for NO₂, both SPM and PM_2.5 levels did not drop significantly even after the standards were introduced.

Fig. 8.3

Source MOE “FY 2019 Environmental Health Surveillance for Air Pollution,” adopted by the authors

SPM and PM_2.5 concentrations in Japan.

As we see in Figs. 8.1, 8.2, and 8.3, the levels of all pollutants were higher at roadside stations than general stations, indicating that air pollution is more severe in stations that are closer to emission sources. Achievement rates for photochemical oxidants are extremely low; only 0.2% of the monitoring stations (2 of 1,166 stations) managed to meet the standard. However, emissions of VOCs, which cause the generation of SPM and photochemical oxidants, have been decreasing over years. VOCs emissions are regulated under the air pollution control law, by which large sources of VOCs are designated as “VOCs emissions facilities” and emissions standards are set in accordance with facility type and size.

4 Air Pollution Policies in Japan

4.1 Point Sources

In conjunction with the air quality standards, the government and regulatory authorities imposed direct control measures. For example, based on the assumption that high concentrations of pollutants are responsible for the air pollution, the government introduced the K-value regulation by which industries were required to install taller smokestacks or increase the rate at which smoke from the stacks rose to dilute the concentrations. The regulation was named so because a “K-value” (where the letter K stands for the ground level concentration of SOx and its value varies from area to area (ERCA, 1997) ) was included in the formula that determines the height of the stack and the velocity. The effect of making the stacks taller was limiting, given the number of factories at the time; even if individual stacks were made taller, there were too many stacks to reduce the concentrations.

Regulations were also introduced on the sulfur content of fossil fuels to control SO₂ and dust emissions. Accordingly, industries were regulated with regard to the types of fuels to use and prompted to switch to low-sulfur fuels, a more expensive alternative. They were also encouraged to adopt flue gas desulfurization (FGD), a piece of equipment that absorbs and removes SO₂ by chemical reaction before it is released from stacks. While not popular at first due to the high initial cost, FGD has made significant improvements and then became widely adopted afterwards (Fig. 8.4). It is commonly used in factories and power plants even today.

Fig. 8.4

Source MOE “FY2004 Environmental Health Surveillance for Air Pollution”

Number of FGD installed in facilities.

Many firms have implemented FGD also because they are charged with the SO₂ levy if their emissions are greater than the specified level. Because they are monitored emissions and imposed the levy accordingly, they have the incentive to adopt FGD and lower their emissions. The levy serves as an environmental tax on SO₂ emissions, as it is charged to polluters based on their emissions volume and used to finance the compensation of the air pollution victims. The levy was introduced to 12 regions initially in 1974 and then expanded to 41 regions in 1978. The rate differs across regions. A fee per unit of pollution discharged is higher for facilities in regions where the concentrations are higher. The levy was imposed on more than 8,000 facilities and the cumulative total of compensation reached 100 billion JPY by 1978 (ERCA 1997).

Figure 8.5 shows changes in the declared amount of the levy. We can see that the amount increased in the 1970s and 1980s when the economic growth rate was relatively high. According to ERCA (1997), the imposition of the levy encouraged facilities to install FGD and thereby contributed to improving air quality in Japan. As air pollution improved, the number of victims and the amount of compensation decreased; as shown in Fig. 8.5, the total amount of compensation payments has been declining constantly since 1990.

Fig. 8.5

Source ERCA (1997), “The Declared Number and Amount of the Pollution Load Levy”

Changes in the levy amount.

Although the emissions decreased with more FGDs being adopted in facilities, the number of pollution patients did not decrease immediately. To compensate the same number of patients as before, the levy rate had to be increased over time. It was 15.84 JPY in Osaka when introduced first in 1974 and then surged up to 532.90 JPY by 1987. Good progress was made but nevertheless, the regulatory measures on individual firms were not sufficient to resolve the air pollution problems. The government thus introduced the total emission control and allocated emission allowances to facilities in severely polluted regions. Being vintage differentiated regulation, it imposes more stringent requirements on later entrants than on existing facilities.

4.2 Mobile Sources: Vehicle Emission Standards and Vehicle Type Regulations

Apart from regulations on point sources, measures were also imposed on mobile sources (e.g., gasoline and diesel vehicles), which accounted for a substantial proportion of air pollution. For example, the SO₂ levy is charged to vehicle owners as well in the form of the automobile tonnage tax, as it was stipulated that 80% of the health compensation should be financed through the levy on point sources and the remaining 20% on mobile sources when the Pollution-Related Health Damage Compensation Law was introduced. The tax is based on the weight of the vehicle, not on the distance traveled or the amount of gasoline consumed by the vehicle.

As noted earlier, while SO₂ concentrations dropped significantly (Fig. 8.1), other pollutants such as NOx and SPM did not decrease to the target levels (Figs. 8.2 and 8.3). Given that automobiles were responsible for more than half of the total NOx emissions, the government introduced a regulation known as the vehicle unit regulation. It applied exclusively to brand new vehicles and controlled chemical substance emissions per kilometer of vehicle travel by imposing an emission intensity limit (i.e., an upper limit on emissions generated per unit of activity).

Accordingly, standards for mobile sources were set for carbon monoxide (CO) in 1966, then for nitrogen oxide (NOx) and hydrocarbons (HC) in 1973, and finally for suspended particulate matter (SPM) in 1993, with the target level for each pollutant becoming tighter over years. Figure 8.6 shows the achievement rate for NOx standards where the vertical axis shows the rate of achievement. We can see that the standards were not met even by the 1990s and that the rate was particularly low at roadside stations.

Fig. 8.6

Source MOE “Annual Reports of Environmental Health Surveillance for Air Pollution,” adopted by the authors

Achievement rate for NOx standards in regions subject to the automobile NOx law.

Figure 8.7 shows the upper limit of NOx emissions per year on a scale of 0–1.2, with 1 being the emissions volume before the standard was implemented. We can see that the emission limit has been significantly tightened over years and currently it is 0.05 as of 2021. One caveat in the regulation was that it applied exclusively to new vehicles to be sold, while there were many “old” vehicles on the road to which the standards did not apply. Because vehicles are, once sold as new, usually used for more than 10 years, the regulation did not contribute to decreasing emissions from vehicles already in use that have higher environmental impacts.

Fig. 8.7

Source The Osaka Prefectural Government, “FY2013 Osaka Environmental White Paper,” The Ministry of Land, Infrastructure, Transport and Tourism, “Emission Regulations on New Vehicles,” adopted by the authors

Changes in NOx emission limits.

To cope with this problem, the government enforced the Automobile NOx Law⁷ in 1992. Under this law, vehicles were banned from passing inspection and renewing their registration after certain years of usage. It is called vehicle type regulation because terminal years were determined by vehicle type. Because it is illegal to register vehicles that have failed inspection, the law directly regulated the use of old vehicles that generate higher levels of pollution. The vehicle type regulation was the nation’s first and it was considered an innovative measure at the time across the world, as it was one of the first policies that restricted the use of older vehicles to curb their emissions. Implemented in 196 municipalities in 6 prefectures (Tokyo, Saitama, Kanagawa, Chiba, Osaka, and Hyogo) where air pollution was particularly severe, the regulation aimed at promoting the replacement of old vehicles in use with new ones with better emissions standards. However, its effectiveness was limited, as shown in Fig. 8.6; the rate of achieving the target NOx (PM) level was only 43% (36%) at roadside stations in metropolitan areas in 1998.

Given that NOx concentrations did not decrease significantly and also, given the need to control PM emissions, which remained unregulated until the vehicle unit regulation was implemented in 1993, the Automobile NOx Law was revised and replaced in 2001 by the Automobile NOx/PM Law (Iwata and Arimura 2009).⁸ The revision aimed at improving the concentration levels of NOx and PM. Under the new law, specified areas were extended into the Nagoya region, consisting of 276 municipalities in total. Just like its predecessor, the Automobile NOx/PM Law includes vehicle type regulation that designates the maximum age limits on vehicles.⁹ The measure, together with the mandatory installation of PM removal equipment (DPF) in Tokyo and other regions, effectively improved both the concentration levels and achievement rates of NOx and PM₁₀ emissions (Arimura and Iwata 2015b).

4.3 Economic Analysis of Air Pollution Regulations: A Case of the Vehicle Type Regulation

Once imposed, policy measures should be assessed on their outcomes and modified as necessary to improve their effectiveness, but how can they be evaluated from an economic perspective? To demonstrate an example of economic analysis of air pollution policies, this section will present findings in Arimura and Iwata (2015a) that examine the costs and benefits of the vehicle type regulation. The regulation was implemented under the Automobile NOx/PM Law to prohibit the use and registration of vehicles, particularly freight trucks, that fail to meet specified emission standards. It sets terminal years for old vehicles in the regulated area and enforces their earlier replacement with new ones.

To comply with the regulation, vehicle owners (e.g., firms in the logistics industry) must secure financing for the earlier replacement of their old vehicles. The net present values differ depending on when they replace their vehicles, say, now as opposed to five years from now. The difference can be considered as the cost of complying with the regulation. In Arimura and Iwata (2015a), the regulation’s costs are calculated by the bottom-up estimating method. That is, they first estimate the costs for individual vehicles and then aggregate the costs for all vehicles subject to the regulation to arrive at the total costs associated with implementing the regulation.

According to their estimation, the cost of a standard freight truck ranges from 150,000 to 430,000 JPY and the total costs of compliance (i.e., the costs for all regulated vehicles, including small cargo, passenger cars, and special vehicles) is 521 billion JPY. The regulation’s benefits are estimated in their study by summing reductions in the external costs of both NOx and PM emissions, which was achieved by the mandatory replacement of old vehicles. According to their estimation, the benefits resulted from reducing NOx and PM₁₀ emissions were 138.9 billion JPY and 1,063.4 billion JPY, respectively. The net benefits (i.e., the sum of the benefits minus the total costs) was estimated to be 681.2 billion JPY, indicating that the policy implementation resulted in a considerable net benefit to society.

It should be noted, however, that the regulation might not have been the most desirable policy option; as discussed in Chap. 2, the regulations are inefficient because the marginal abatement costs differ across polluters. The vehicle type regulation is an example of command-and-control regulations. The authors thus examine a case with an optimal policy that maximizes social surplus, namely an environmental tax, and compared its net benefit with that of the regulation. It was found that the net benefit of the tax imposition would be 1,388.4 billion JPY, almost double that of the regulation. One might argue that taxation is not a practical option because significant burden would be borne by affected parties. In response to this concern, the authors show that even a minor modification to the existing policy can make a substantial change; simply shortening the age limits of vehicles by one year would increase the net benefit by 10%. Findings in their study demonstrate that economic assessments of policy options provide policy makers with key information about them, including which option maximizes net benefit to society and whether the existing policy is implemented efficiently.

Box 8.1. Pollution Control Agreements in Japan

Pollution control agreements (PCAs) are voluntary environmental agreements (VEAs) between a local government and facilities. Japanese VEAs are one of the world’s oldest experiments in voluntary policy. The first agreement was in 1952, when Shimane Prefecture signed a memorandum of understanding with the Masuda Mill of Daiwa Boseki Co., Ltd. (now Daiwabo Holdings Co., Ltd.) and the Gotsu Mill of Sanyo Pulp Co., Ltd. (now Nippon Paper Industries Co., Ltd.). In 1964, Yokohama City and Electric Power Development Co. (now known as J-Power) concluded an agreement stipulating specific and detailed numerical values. This agreement triggered the nationwide spread of PCAs.

Unlike pollution regulations based on laws and ordinances, PCAs are based on voluntary agreements; however, they are beneficial to both local governments and businesses. Local governments can take tailored and detailed pollution prevention measures that fit the needs and conditions of the regions. PCAs can also implement stricter standards (i.e., agreed values) that exceed the laws but legality will not be questioned, compared with regulations. For business operators, concluding PCAs with local governments enables them to build relationships with governments and communities and reduces resident opposition to business activities.

A detailed explanation and discussion of the Japanese PCAs can be found in Welch and Hibiki (2002) and Welch and Hibiki (2003).

(by A. Hibiki)

5 Air Pollution in Developing Countries

Although air pollution has improved significantly in Japan, it still poses environment and health risks globally. International Energy Agency (IEA 2023) estimates health damage from air pollution as the world strives for carbon neutrality by 2050 (see Chap. 9 for further discussion). It reports that even under the scenario of carbon neutrality, ambient air pollution caused 4.4 million premature deaths in 2022 and will cause 4.3 million premature deaths in 2025, as shown in Table 8.1. IEA also predicts that even if the world achieves carbon neutrality in 2050 and reduces the usage of fossil fuel drastically, 0.7 million people will die prematurely due to ambient air pollution. European Environmental Agency estimates that fine particulate matter (PM_2.5) and NOx caused 253,000 deaths and 52,000 deaths, respectively, in EU-27 countries in 2021.¹⁰ The problem is even more severe in emerging market and developing countries, especially in Asia. According to State of Global Air,¹¹ 1.85 million deaths in China and 1.67 million deaths in India in 2019 are attributable to ambient air pollution.

Table 8.1 Air pollution damage under net zero scenario

Among various pollutants, PM_2.5 in particular poses the greatest threat to human health (UNEP 2018). McDuffie et al. (2021) found that 1.05 million deaths worldwide could have been avoided in 2017 if fossil combustion had been eliminated, which would have resulted in the reduction of PM_2.5 emissions by 27%. As we will show in Chap. 9, coal has the highest carbon intensity per unit of energy among fossil fuels. Coal combustion for energy production and industry as well as for residential heating is the largest source of air pollution in China, accounting for 40% of PM_2.5 concentrations in 2013 (ADB 2021).

The heavy reliance on coal and biomass to meet energy needs also causes air pollution and particulate matter emissions in developing countries. For example, while India has implemented policies to shift to renewable energy, its primary energy mix is dominated by fossil fuels, with coal contributing 44%, oil 25%, and biomass 13% (ADB 2021), which increases the risk of worsening air quality in the country. According to the Paris Agreement scenario (see Chap. 9 for details), Southeast Asian countries such as Indonesia, the Philippines, and Vietnam also continue to increase coal usage to meet their energy needs (IEA 2022).

India and China have some of the most polluted cities in the world. Average annual exposure to fine particulate matter in cities such as New Delhi and Ahmedabad in India and Shijiazhuang in China is more than ten times the WHO’s annual mean value: ten micrograms per cubic meter (ADB 2021). Although efforts have been made to reduce air pollution caused by vehicle emissions, inefficient diesel and two-stroke engines are still used, contributing to NOx and particulate matter emissions. In addition, the number of vehicles increased in urban areas while road capacity remains the same, resulting in more pollutant emissions per kilometer (ADB 2021).

To combat air pollution in developing countries, it might be effective to introduce a levy on pollutants, as the one imposed in Japan on SO₂ emissions. Emissions trading schemes may also be effective if they target factories and power plants. China and India introduced carbon emissions trading schemes as climate change countermeasures (see Chap. 9 for further discussion). Air quality in Beijing improved significantly after the ETS was implemented. The ETS contributed to decreasing coal consumption and consequently reduced both CO₂ emissions and air pollution. The achievement suggests that policies are more likely to be implemented and practiced effectively if they are air pollution policies complementing climate change measures, or vice versa, if they are climate change policies complementing air pollution measures.

Green vehicles (e.g., electric vehicles and fuel cell vehicles), which were not available when Japan was coping with air pollution, are a powerful substitute for conventional vehicles to curb vehicle emissions. Electric vehicles run on electricity and emit no pollutants when running. The same applies to fuel cell vehicles that uses hydrogen. If electricity is generated from renewable energy sources, CO₂ will not be produced. Promoting the use of electric vehicles can be an effective measure to reduce both air pollution and global warming. Apparently, the rapid shift to electric vehicles is due in large part to the fact that they can serve the double purpose of mitigating pollution and climate change.

6 Household Air Pollution in Developing Countries

Another major concern in developing countries is household air pollution. Continued exposure to household air pollutants is as harmful to public health as outdoor air pollution, as discussed in IEA’s special report on energy and air pollution (2016). Household air pollution results from the use of solid fuels such as firewood and cow dung for cooking and heating. Residents of rural areas in some countries in Asia and Africa rely on solid fuels due to not having access to electricity. Incomplete combustion of those fuels in inefficient cooking stoves contributes to high PM concentrations in the indoor environment and causes respiratory health problems, ultimately leading to premature deaths. The use of candles and kerosene lamps for indoor lighting causes similar problems.

Pollution levels in kitchens in developing Asian countries often exceed the EPA guideline values. For example, the 24-h average PM_2.5 concentration in kitchens in India where solid fuels are used for cooking is reported to be about 609 mg/m³ (Balakrishnan et al. 2013). According to WHO (2018), despite the alarming health risks of household air pollution, about 3 billion people worldwide, mainly in India and China, still rely on solid fuels to meet their household energy needs.

Commercial clean fuels are either expensive or in short supply for about 2.8 billion households worldwide (among which 500 million resides in urban regions), giving them little incentive to switching to cleaner fuels. IEA (2017) estimates that unless drastic changes are made by policy interventions, the number of people relying on polluting cooking fuels will remain largely unchanged until 2030. According to IEA (2016), almost 3 million premature deaths are linked to household air pollution annually, among which 500,000 deaths occurred in sub-Saharan Africa alone. The report predicts that 360,000 people will die prematurely by 2040, even though indoor air pollutant emissions and their damages are on a declining trend.

Improved cook stoves have been adopted as a potential solution, as they halve the consumption of firewood. However, IEA’s special report points out that using improved stoves will not be a fundamental solution as it still contributes to PM_2.5 emissions. Although electrification can be another solution, technical challenges remain because power grids are not well established in developing countries, particularly in rural areas. Even if electric stoves become available, many may prefer cooking with firewood as it is considered to produce better tasting food. Practical challenges persist in the implementation of other alternatives such as solar lanterns that are difficult to cook with due to their low output.

Using firewood for cooking causes problems other than household air pollution and health damage. Deforestation due to excessive firewood harvesting is one such example. Another is gender inequalities; it is women (as well as children) who mainly engage in harvesting and collecting firewood, and the labor-intensive and time-consuming duty hinders women from entering the workforce. Household air pollution is partly attributed to poverty, health, gender, and environmental issues, all of which are included in the 17 Sustainable Development Goals. Transition to clean cooking fuels and technologies is therefore integral to achieving many points of the SDG agenda.