Framing the Problem

• Transboundary nature of PM2.5 pollution in Japan is the most difficult component of the issue to solve, creating wicked nature of the problem. Hence, this is number one in terms of issues associated with PM2.5 pollution.

• Yonago City, Japan (Oct 2015 – July 2016), reveals four major air pollution events with Episode I dominated by nitric aerosols, Episodes II and III by Asian dust, and Episode IV by sulfate aerosols. Global chemical transport models and backward trajectories confirmed these pollutants originated from external sources, highlighting the challenge of cross-border air pollution (Figure 4) (Onishi et.al., 2025).

• Emissions from mainland China may contribute up to 50–60% of the annual mean PM2.5 concentration in Western Japan and approximately 40% in the Kanto region, which can be observed in Figure 5 (Botta & Yamasaki, 2020). 

• As seen in the image below from IQAir's live data on air quality, Japan's location downwind of arid regions and rapidly developing Asian countries has intensified PM2.5 pollution and visibility issues associated with it (Figure 6). Transboundary pollution is reported to exceed local sources, particularly in western Japan, though its impact varies with climate patterns and wind direction (Figure 4) (Onishi et al., 2025).

• While China remains primarily focused on its economic development, rather than international cooperation on limiting PM 2.5, it prioritizes air quality standards within its urban centers due to the serious health hazards from this air pollution (Xie & Liao, 2022).

Q: Why is it Dangerous?

A: Air pollution consists of a combination of pollutants such as nitrogen dioxide (NO2), sulphur oxides (SOx), volatile organic compounds (VOCs), and suspended particulate matter (PM) of different sizes (PM10, PM2.5, coarse particles). Of these, PM2.5 is the most significant threat to the health of those who have been exposed to it. This is due to its microscopic size of just 2.5 microns, which allows it to be easily inhaled into the lungs where it accumulates in the bronchial tubes that lead to each of the lungs, as pictured in Figure 9 (IQAir, 2023). Aside from the deadly nature of the pollutant, Japan has a dense population (>80%) residing near pollution hotspots such as urban regions thus, strengthening the inability to mitigate health-related impacts (Goto et al., 2016). 

• Air quality policies are fragmented across multiple ministries, lacking a formal coordination mechanism, leading to inconsistent regulatory approaches. 

• Despite the Ministry of Environment's budget nearly tripling from 2000 to 2017, resources for air quality remained stagnant. 

• Prefectures and lower levels of government, has limited power over air quality control as central government retains monitoring in response to nuclear matters instead of air quality standards. 

• Mitigating industrial emissions is challenging, as imposing charges on industries to meet air quality standards often leads to increased production costs, hence big industry players are subject to resist policy. 

(Botta & Yamasaki, 2020; Cole, 1994) 

• In the 20th century, Japan underwent rapid industrialization, particularly since the 1950s. Industry flourished at a very rapid pace which caused problems in air quality, including the exponential increase in PM 2.5 (Wakamatsu et al., 2013).

• This expansion of industry, coupled with population growth and increased construction, occurred in the absence of established air quality standards, as the Air Pollution Control Law (APCL) was only introduced later. This lack of regulation contributed significantly to the exacerbation of air pollution, including rising levels of PM 2.5. (Figure 8) (Wakamatsu et al., 2013).

• Scientific data on PM2.5 is crucial as it reflects the severity of the issue, but data limitations can distort findings by overlooking or underestimating key causes. However, compared to other factors discussed above, it is considered the least critical dimension in addressing PM2.5 pollution.

• International efforts to reduce PM2.5 mainly involve data collection from China, Korea, and Japan, but differing domestic air quality standards hinder the development of effective collective agreements (Kim et al., 2021). 

• Outdated datasets compromise accuracy, as many studies still use emission inventories like MEIC 2010 or INTEX-B 2006. This fails to reflect significant reductions in China’s anthropogenic emissions from 2013 to 2017, such as a 59% drop in SO₂ and a 33% decrease in PM2.5 (Liu, Li, & Yao, 2022).

• In Japan, 94.2% of monitoring stations recorded PM2.5 levels exceeding PM10 in at least 1% of records. Among the 1,074 PM2.5 monitoring stations, 20.3% recorded over 1% and 3.4% recorded over 5% of repeated PM2.5 measurements (Liu, Li, & Yao, 2022).

• Many Source-Receptor Relationship (SRR) studies focus on short-term pollution episodes, leading to overestimations of transboundary pollution contributions (Liu, Li, & Yao, 2022).

• Limited spatial coverage in air quality models risks misattributing sources, as pollutants from regions like the Indo-China Peninsula and Central Asia are often overlooked despite their significant contributions to East Asian air pollution (Liu, Li, & Yao, 2022).

Figure 13: Mind map relating to the issue of air pollution in Japan, highlighting the main topics: Impacts, Causes, Initiatives, and Challenges. Missing is the topic of Governance and the organizations involved.