Glyoxal is one of the smallest dicarbonyl compounds existing in both the gas phase and in an aerosol. The primary sources of glyoxal have been known to be the photochemical products of the non-methane hydrocarbons. Since the heterogeneous reactions of glyoxal play an important role in the formation of secondary organic aerosols, the studies of the formation process and sources of glyoxal have been reported. However, the reports for the ambient measurements of glyoxal are limited. In this study, the ambient measurements of gaseous glyoxal by incoherent broad band cavity enhanced absorption spectroscopy (IBBCEAS), a novel technique for the measurements of trace species, were carried out in the field museum of Tama hills (FM Tama) maintained and operated by the Tokyo University of Agriculture and Technology during the summer season, July 31–Aug. 7, 2015. During the measurement periods, the average concentration of gaseous glyoxal was 0.24±0.18 ppbv, comparable to the previous measurements in urban areas. From the correlation with gaseous glyoxal and trace species, it is indicated that the sources of glyoxal around the measurement point were photochemical products.

The PM_2.5 concentration decreases between 2013 and 2016 over Japan were analyzed by observation and a chemical transport model. During this period, the annual mean PM_2.5 decreased in Japan and the number of PM_2.5 sub-standard days underwent a dramatic reduction. Our analysis confirmed that the PM_2.5 in northern China, SO₂ and NO₂ vertical column density over Central East China by satellite showed about a 10%/y reduction and this happened due to the anthropogenic emission reductions (almost 10%/y reduction). A Source-receptor analysis by a chemical transport model showed that a 20% reduction of the Chinese PM_2.5 concentration will decrease the annual mean PM_2.5 in Fukuoka by 12%. Our analysis indicated that if the current emission reduction rate continues over China, the high concentration of transboundary PM_2.5 problem in Japan will very quickly improve.