Characteristics of Polycyclic Aromatic Hydrocarbons (PAHs) and Common Air Pollutants at Wajima, a Remote Background Site in Japan

Abstract

Background: Background sites are mainly affected by long-range-transported air pollutants, resulting in potential adverse effects on local atmospheric environments. A 4–5 year observational study was conducted to illustrate the air pollution profile at the Kanazawa University Wajima air monitoring station (KUWAMS), an ideal remote background site in Japan. Methods: Nine polycyclic aromatic hydrocarbons (PAHs) in the particulate phase and various air pollutants were continuously monitored for 4–5 years. Diagnostic ratios of PAHs and back-trajectory analysis were applied to trace the possible sources of the air pollutants collected at the sampling site. Results: The atmospheric concentration of PAHs in the atmosphere at the site decreased from 2014 to 2019, benefit from the predominant air pollution control policy in China and Japan. Common air pollutants including sulfur dioxide (SO2), nitrogen oxides (NOx), ozone, methane (CH4), and non-methane hydrocarbon (NMHC) were detected in low concentrations from 2016 to 2019, while ozone (O3) and particulate matter (PM2.5, PM with a diameter less than 2.5 μm) were present in high levels that exceeded the Japanese standards. Most air pollutants peaked in spring and showed evident diurnal variations in spring and summer. Conclusions: This is the first study to clarify the atmospheric behaviors of multiple air pollutants at a background site in Japan. Significant external air pollutant impact and unneglectable air pollution were demonstrated at KUWAMS, indicating the importance of studying atmospheric pollution at remote sites.

Impact of the COVID-19 Outbreak on the Long-range Transport of Particulate PAHs in East Asia

“…The filter was replaced once a week from November 2, 2019, to April 25, 2020. Based on the prevailing period of the East Asian winter monsoon, this sampling period was defined as the cold season, which extended from November to May in the previous observations (Tang et al, 2015;Zhang et al, 2020e).…”

“…Meteorological parameters included temperature, relative humidity (RH), pressure, wind speed, and rainfall. The details of meteorological monitoring are provided elsewhere (Zhang et al, 2020e).…”

“…Airborne particles carrying PAHs can participate in the short-and long-range transport of air masses (Zhang et al, 2020b). Although the physical and chemical behavior of PAHs during transport may lead to the loss of PAHs in particles, the enhanced health risks caused by PAHs transported to the recipient site cannot be ignored (Lee et al, 1995;Sheu et al, 1997;Zhang et al, 2020e).…”

“…These activities not only increase the load of atmospheric PAHs in China but also worsen air pollution in downwind countries and regions (Pan et al, 2015;Inomata et al, 2017;Li et al, 2018). The observations over 15 years at Kanazawa University Wajima Air Monitoring Station (KUWAMS), a remote background site in Japan, provide hard evidence of the transport of pollutants (Tang et al, 2005;Yang et al, 2007;Tang et al, , 2015Zhang et al, 2020e). Driven by the East Asian monsoon system, polluted air masses in northern China can be transported to Japan with Northwest winds from November to May of the following year (the cold season); between June and October (the warm season), the airflow is driven by southerly winds from the North Pacific (Tang et al, 2015).…”

“…1) (Tang et al, 2015;Zhang et al, 2020e), with increased PAHs in the cold season and decreased PAHs in the warm season. In addition, the mitigation of air pollution in response to control measures taken by China, for example, the interim control measures for the 2008 Beijing Olympic Games (BMEPB, 2008), the Air Pollution Prevention and Control Action Plan implemented from 2013 to 2017 (State Council, PRC, 2013), and the clean energy heating project launched in northern China since 2017 (NDRC, 2017), has been reflected in the long-term observations at KUWAMS (Tang et al, , 2015Zhang et al, 2020e). Although KUWAMS is sometimes affected by polluted air masses in Japan, the level of atmospheric PAHs in Japanese cities is two orders of magnitude lower than that in China (Morisaki et al, 2016).…”