Environmental Research Letters (Jan 2024)
Dramatic improvement of aerosol pollution status over the East Asian ocean: from the establishment of Japanese environmental quality standard for PM2.5 in 2009 to its achievement in 2021
Abstract
The severe aerosol pollution in East Asia has been a focus of much research. In Japan, the environmental quality standard (EQS) for PM _2.5 was established in 2009 (daily average, 35 μ g m ^−3 ; annual average, 15 μ g m ^−3 ), and its achievement rate was below 50% during the early 2010s. Then, the PM _2.5 concentration gradually decreased, the achievement rate improved, and the EQS for PM _2.5 was finally achieved (100%) in fiscal year (FY) 2021. Because transboundary aerosol pollution is an important factor in Japanese air quality, here we analysed the long-term dataset of the satellite-measured fine-mode aerosol optical depth (AOD _f ) over the East Asian ocean to reveal the changes in the transboundary aerosol over East Asia. Overall, a decrease in AOD _f was seen over the entire East Asian ocean during the period analysed. A gradual declining trend in AOD _f was measured (−4% to −5%/year over the adjacent ocean around Japan) and corresponded well to the trend in PM _2.5 concentration observed in Japan (−5.3%/year) during FY2010–FY2021. Due to the domestic contribution in Japan, the negative trend was slightly greater for Japanese PM _2.5 concentration than for AOD _f over the adjacent ocean around Japan, and we concluded that the main reason for the dramatic air quality improvement in PM _2.5 in Japan was driven by the improvement of transboundary aerosol pollution over East Asia. In addition, the 12 year analysis period (FY2010 to FY2021) was divided into three parts: stagnation (FY2010 to FY2014), in which PM _2.5 and AOD _f remained the same as they were in FY2010; improvement (FY2015 to FY2018), in which PM _2.5 and AOD _f declined dramatically; and achievement (FY2019 to FY2021), in which PM _2.5 and AOD _f declined further.
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