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To better understand seasonal variations in the components of PM_〈2.5〉 and related trace gases, and the impacts of long-range transport from the Asian continent to Japan, we analyzed long-term, simultaneous observations of fineand coarse-mode nitrate, related aerosol components (SO_4^〈2-〉, NH_4^+, BC, OC), and trace gases (CO, NH_3, HNO_3) around the Chikushi Campus of Kyushu University, Fukuoka (33.52°N, 130.47°E), from August 2014 to October 2015. Daily and monthly mean aerosol concentrations were analyzed to assess the main seasonal variation in pollution. We found that fine aerosols (fSO_4^〈2-〉, fNO_3^-, and fNH_4^+) explained most of the seasonal change in PM_〈2.5〉. Polarization optical particle counter measurements were useful for detecting the onset of dust transport from the Asian continent, and we observed high concentrations of coarse-mode NO_3^- (cNO_3^-) during dust period, which indicated the formation of dust nitrate during transport. We also analyzed diurnal variation in the basic aerosol components for different seasons, weekday/weekend effects (for CO, BC, and NH3), and sensitivity on days with and without precipitation (for CO, BC, NH_3, PM_〈2.5〉, and PMc). Observational data for HNO_3, fNO_3^-, and cNO_3^- demonstrated that cNO_3^- accounted for the largest proportion of total nitrate (defined as the sum of fNO_3^-, cNO_3^-, and HNO_3), constituting 40–55% of the total nitrate during the winter, whereas HNO_3 gas constituted approximately 40% of the total nitrate in summer and fNO_3^- peaked during the winter.

Atmospheric ammonia (NH_3) plays an important role in the formation and understanding of secondary inorganic aerosols, but has not been examined using chemical transport models (CTMs) and atmospheric levels have not been compared with satellite observations. Here, we analyzed the seasonal variation in atmospheric NH_3 using long-term hourly NH_3/NH_4^+ measurements made at the Chikushi Campus of Kyushu University in Fukuoka, nationwide filter pack (FP) network observations over Japan, GEOS-Chem CTM results, and Infrared Atmospheric Sounding Interferometer (IASI) satellite retrievals over East Asia. We found that the IASI NH_3 retrieval over central and north China had a strong correlation with the CTM results (R = 0.74). There was a similar correlation over south China, but the IASI NH_3 retrieval was only 48% of the CTM value. CTM results over Japan reproduced the major seasonal variations compared with surface observations, but IASI observations over Japan were below or near the detection limit and it was difficult to obtain a reasonable correlation with measurements.

We improved two-wavelength polarization Mie-scattering lidars at several main sites of the Asian dust and aerosol lidar observation network (AD-Net) by adding a nitrogen Raman scatter measurement channel at 607 nm and have conducted ground-based network observation with the improved Mie–Raman lidars (MRL) in East Asia since 2009. This MRL provides 1 α+ 2 β +1 δ data at nighttime: extinction coefficient ( α 532 ), backscatter coefficient ( β 532 ), and depolarization ratio ( δ 532 ) of particles at 532 nm and an attenuated backscatter coefficient at 1064 nm ( β at ,1064 ). Furthermore, we developed a Multi-wavelength Mie-Raman lidar (MMRL) providing 2 α +3 β +2 δ data ( α at 355 and 532 nm; β at 355 and 532; β at at 1064 nm; and δ at 355 and 532 nm) and constructed MMRLs at several main sites of the AD-Net. We identified an aerosol-rich layer and height of the planetary boundary layer (PBL) using β at ,1064 data, and derived aerosol optical properties (AOPs, for example, α a , β a , δ a , and lidar ratio ( S a )). We demonstrated that AOPs cloud be derived with appropriate accuracy. Seasonal means of AOPs in the PBL were evaluated for each MRL observation site using three-year data from 2010 through 2012; the AOPs changed according to each season and region. For example, S a ,532 at Fukue, Japan, were 44±15 sr in winter and 49±17 in summer; those at Seoul, Korea, were 56±18 sr in winter and 62±15 sr in summer. We developed an algorithm to estimate extinction coefficients at 532 nm for black carbon, dust, sea-salt, and air-pollution aerosols consisting of a mixture of sulfate, nitrate, and organic-carbon substances using the 1 α 532 +2 β 532 and 1064 +1 δ 532 data. With this method, we assume an external mixture of aerosol components and prescribe their size distributions, refractive indexes, and particle shapes. We applied the algorithm to the observed data to demonstrate the performance of the algorithm and determined the vertical structure for each aerosol component.

Heterogeneous processes play an important role in changing the chemical, physical, optical, and radiative characters of dust particles at regional and global scales, especially in East Asia, where both the emissions of mineral dust and anthropogenic pollutants are huge. To investigate the chemical and physical impacts of heterogeneous reactions on dust particles, three dust and/or air pollution episodes were observed and simulated in Beijing, China and Fukuoka, Japan during 27 March and 2 April, 2015. The results confirmed that heterogeneous reactions were the major mechanisms producing coarse mode nitrate reaching 19 μg/m^3 in Beijing and 4 μg/m^3 in Fukuoka. We also found that heterogeneous processes and subsequent hygroscopic growth significantly changed the mixing state and size of dust particles. As a result of the internal mixing of nitrate, sulfate, and aerosol liquid water, the volume concentration of dust doubled when the relative humidity (RH) was relatively high (>80%), and the dust particles tended to be spherical when the volume fraction of dust coatings reached 20%.

Mass concentrations of chemical compounds in both fine (particle diameter, Dp < 2.5 μm) and coarse mode (2.5 < Dp < 10 μm) were measured in urban sites of the Fukuoka area using a continuous dichotomous Aerosol Chemical Speciation Analyzer (ACSA-12) at a time-resolution of 1 h throughout 2014. We found that mass concentrations of particulate matter (PM), sulfate, and water-soluble organic compounds in fine mode showed a predominant peak during the spring, indicative of long-range transport due to the prevailing westerly wind. Nitrate mass in fine mode showed an obvious warm-season-low and cold-season-high pattern; thus, it was difficult to accurately quantify the cross-boundary transport of nitrate because of the gas-aerosol phase equilibrium process, particularly under high temperature conditions. Mineral dust and sea salt were the two most important medians carrying coarse mode nitrates. This study found that the transported anthropogenic pollutants contributed to ambient PM mass in Fukuoka city, although urban emission was not negligible.

[ABSTRACT] We propose a simple method of detecting dust-loaded airmass over the land area, which is based on the difference between Rayleigh-corrected reflectances at 412 nm and 443 nm bands of SeaWiFS data. The method, together with multi-band based cloud masking algorithm, is applied to '98 April SeaWiFS images of continental China, when a major dust event occurred. The resulted "dust aerosol index" imageries are compared with dust amount distribution predicted by a dust transport model, showing good general agreement. The correlation of the satellite-derived index and the predicted dust amount is discussed from the viewpoint of difference in the land cover.

[ABSTRACT] The NOAA/AVHRR images of the brightness temperature difference of 11 and 12μm bands are utilized to detect Asian dust events during 1997-2000, and compared successfully for the events in 1998 and 2000 with the results of an on-line dust tracer model coupled with Regional Atmospheric Modeling System taking into account the surface wind, vegetation and snow coverage. The GMS-5/VISSR images of the same type are also useful to detect the dust events with its high frequency of observation and wide spatial coverage, though the sensitivity to diffused dust is inferior to the AVHRR.