Transboundary transport of atmospheric aerosols to Japan is a well-known atmospheric phenomenon. In recent years, air quality has become a higher concern for many people in Japan because of occasional PM2.5 issues due to transboundary transports. Therefore, monitoring air quality in Japan and examining the causes of poor air quality are important for the well-being of the Japanese people, at present and in the future. In this talk, I will introduce two topics related to air quality in Japan from our recent studies. Here, I focus on Northern Japan (i.e., Hokkaido prefecture). These topics are discussed mainly using observations from Hokkaido and NASAs MERRA-2 reanalysis data.
The first topic is the successful detection of an event involving the transport of Asian dust (called Kosa in Japanese) to Sapporo city in Hokkaido on March 7, 2016, though the Japan Meteorological Agency (JMA) did not report any Kosa transport to Japan on that day (https://goo.gl/z8R5he). To do this, we used a special version of low-cost aerosol sensors (Shinyei Technology Co., Ltd.) at Sapporo (Hokkaido University) and Takikawa. The AERONET data at Hokkaido University (https://goo.gl/GGcRbI) and the ground-based lidar data by the National Institute for Environmental Studies (NIES) at Takikawa (e.g., https://goo.gl/iW8IZm) on that day both supported the timing of the Asian dust transport. In addition, provisional PM2.5 data (AEROS: http://soramame.taiki.go.jp/; managed by the Ministry of Environment) and other commercial optical particle counter observations at Hokkaido University showed time-lagged peaks of this Kosa event at later time than when the data from the aerosol sensors showed the peaks. Our results indicate that the low-cost aerosol sensor would be very useful in detecting correct timings of Kosa transport. However, we need to be careful to use the PM2.5 data when we discuss the right timing of Asian dust transport.
The second topic involves an event on July 26, 2014, when Sapporo city warned its citizens for the first time of a severe increase in PM2.5. The city’s examination report concluded that this increase was caused by the transport of smoke created by Siberian wildfires (https://goo.gl/u1doYi). This motivated us to investigate the number of times large biomass burnings over East Eurasia has brought this type of smoke to Hokkaido, as well as the causes of these burnings. The calculated PM2.5 data, based on the MERRA-2 data, well reproduced the timely variation of the observed PM2.5 in Sapporo in July 2014. The observed increase-timings of black carbon (BC) and organic carbons (OC) were also well explained by the reanalysis data, though all the PM2.5, BC, and OC from the MERRA-2 data overestimated the observations. Since 2003, similar transports of smoke to Sapporo have been seen three times (May 2003, April 2008, and July 2014). Upon further analysis of regional relationships between MODIS snow cover fraction and MERRA-2 variables over East Eurasia, we found that these fires were all related to abnormally small amounts of snow (i.e., negative anomalies from the climatologies in 2003-2014), which happened a couple of months before the main fire months. Our results indicate that early-time snow reductions over East Eurasia may cause dryer and warmer conditions in the following months, which can create the conditions that are preferable for generating fires. Eventually, the emitted smoke from these fires can have an impact on air quality in northern Japan.
613 Seminar Series Committee: