Air Pollution Trends in Japan between 1970 and 2012 and Impact of Urban Air Pollution Countermeasures.

Air pollution trends in Japan between 1970 and 2012 were analyzed, and the impact of air pollution counter-measures was evaluated. Concentrations of CO decreased from 1970 to 2012, and in 2012, the Japanese environmental quality standard (EQS) for CO was satisfied. Concentrations of SO₂ dropped markedly in the 1970s, owing to use of desulfurization technologies and low-sulfur heavy oil. Major reductions in the sulfur content of diesel fuel in the 1990s resulted in further decreases of SO₂ levels. In 2012, the EQS for SO₂ was satisfied at most air quality monitoring stations. Concentrations of NO₂ decreased from 1970 to 1985, but increased from 1985 to 1995. After 1995, NO₂ concentrations decreased, especially after 2006. In 2012, the EQS for NO₂ was satisfied at most air quality monitoring stations, except those alongside roads. The annual mean for the daily maximum concentrations of photochemical oxidants (OX) increased from 1980 to 2010, but after 2006, the 98^th percentile values of the OX concentrations decreased. In 2012, the EQS for OX was not satisfied at most air quality monitoring stations. Non-methane hydrocarbon (NMHC) concentrations generally decreased from 1976 to 2012. In 2011, NMHC concentrations near roads and in the general environment were nearly the same. The concentration of suspended particulate matter (SPM) generally decreased. In 2011, the EQS for SPM was satisfied at 69.2% of ambient air monitoring stations, and 72.9% of roadside air-monitoring stations. Impacts from mineral dust from continental Asia were especially pronounced in the western part of Japan in spring, and year-round variation was large. The concentration of PM_2.5 generally decreased, but the EQS for PM_2.5 is still not satisfied. The air pollution trends were closely synchronized with promulgation of regulations designed to limit pollutant emissions. Trans-boundary OX and PM_2.5 has become a big issue which contains global warming chemical species such as ozone and black carbon (so called SLCP: Short Lived Climate Pollutants). Co-beneficial reduction approach for these pollutants will be important to improve both in regional and global atmospheric environmental conditions. [ABSTRACT FROM AUTHOR]