Observed and modeled aerosol compositions at Fukue island in the spring of 2018

Continuous measurement of trace gases and PM2.5 aerosols has been conducted at Fukue Island, which is a remote island in western Japan, since February 2009 (Kanaya et al., 2016). The observation site was located at the Fukue Island Atmospheric Environment Monitoring Station (Fukue site; 32.75° N, 128.68° E). The mixing ratio of CO was measured using a nondispersive infrared (NDIR) CO monitor (model 48C, Thermo Scientific, Inc., USA), and mass concentrations of BC were measured using a Multi Angle Absorption Photometer (MAAP, model 5012, Thermo Scientific, Inc., USA). Details of the CO and BC measurements are outlined in Kanaya et al. (2016; 2020), some of which revealed that the elevated concentrations of CO, and BC at the observation site were mainly affected by the transboundary transport of polluted air masses from the Asian continent (i.e., long-range transport) with negligible impact of local emission sources (e.g., Kanaya et al., 2016). Elemental compositions of PM2.5 aerosols were measured using a Continuous Particulate Monitor with the XRF analysis (PX-375, Horiba Ltd., Kyoto, Japan). The instrumental design is described in Asano et al. (2017). However, the instrument can be briefly described as follows: PX-375 consists of a collection unit for aerosol particles on a filter, the measurement unit for the mass of the collected aerosol particles, and an XRF analysis chamber; the filter tape used for the particle collection was fabricated by Horiba Ltd. (TFH-01, Horiba Ltd.); and TFH-01 is a polytetrafluoroethylene (PTFE) filter with non-woven fabric polyethylene (PE) and polyethylene terephthalate (PET) backing, which was designed to mechanically strengthen the filter structure. The total mass of PM2.5 aerosols collected on the filter was analyzed using a radiocarbon-based beta-ray attenuation method during the particle collection. The 4 hourly PM2.5 mass concentrations measured using the PX-375 were compared with those measured using the SHARP monitor. PX-375-derived PM2.5 mass concentrations were found to be in good agreement (within 10%) with those observed by the SHARP monitor. After sampling, a particle-laden spot on the filter was transferred into the XRF analysis chamber by advancing the filter roll tape and then analyzed by the XRF technique. The ambient air was drawn at 16.7 liters per minute through the PM2.5 cyclone (URG-2000-30EH, URG Corp., North Carolina, USA) into the PX-375 instrument. During the observation period, the PM2.5 aerosol particles were collected for 4 h, and the XRF analyses were performed with 4000 sec of X-ray irradiation at 15 and 50 kV. The typical volume of the sampled air was 4 m3 per particle-laden spot. The limits of detection (LODs) were evaluated by repeated measurements placing the high efficiency particulate air (HEPA) filter in front of the PX-375 to introduce particle-free air into the PX-375. The LODs were defined as three times the standard deviations of the measured values by the PX-375 at the observation site and were evaluated to be 1.57, 0.28, 0.70, 0.69, 25.6, 18.3, 1.95, 8.50, and 9.50 ng m-3 for Fe, Pb, Cu, Mn, K, Cl, Ca, Si, and S as sulfate, respectively. The IMPACT model (Ito and Miyakawa, 2023; and references therein) was deployed to simulate three-dimensional distribution of the atmospheric composition including targeted aerosol species, such as Fe. Ito and Miyakawa (2023) modified the IMPACT model to expand its capability to simulate elements other than Fe, including Pb, Cu, Mn, and Si. They improved the IMPACT model to include metal smelting as an emission source of Fe, which has not well been evaluated in previous studies. The model simulations were performed using a horizontal resolution of 2.0° × 2.5° (latitude × longitude) and 47 vertical layers. An emission inventory, Community Emissions Data System (CEDS, v-2021-02-05, O’Rourke et al., 2021), was used for fine particulate matter and BC emitting from anthropogenic sources. The metal content of PM2.5 aerosols from lithogenic, pyrogenic, and anthropogenic sources was obtained from the compilation of source-specific aerosol measurements (Ito et al., 2018; Kajino et al., 2020; Reff et al., 2009). Because CEDS does not include the emission of BC (a combustion source tracer) from the metal production sector (e.g., the production of iron and steel, aluminum, and other non-ferrous metals), Fe emissions from the metal production sector was estimated by scaling sulfur dioxide (SO2) emission from CEDS based on the relative emissions of Fe to SO2 (Rathod et al., 2020) in each country. 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