Asia Center for Air Pollution Research (ACAP)

Japan Environmental Sanitation Center

Major research

Study on air pollution at Niigata-Maki National Acid Deposition Monitoring Station

Recent Major Research Achievements

<Chemical Characteristics and Source Apportionment of PM2.5 and Long-range Transport from Northeast Asia Continent to Niigata>

During the four seasons from May 2015 to February 2017, seasonal intensive sampling was conducted for two weeks at the Niigata-Maki National Acid Deposition Monitoring Station.

Daily mean concentrations of PM2.5 ranged from 4.2 µg m-3 to 33.4 µg m-3 during the observation period, which was lower than Japanese Air Quality Standard for PM2.5 (35 µg m-3). The higher concentrations of SO42-, NH4 + and organic carbon (OC) were observed in spring and summer, which may result from the photochemical activity and secondary OC production.

The major chemical components of PM2.5 were SO42-, NO3-, NH4 +, OC, elemental carbon (EC) and crustal elements. Compared with data at other urban sites, a lower concentration of EC and NO3- and higher OC/EC ratio were observed at the Niigata-Maki site, which may result from the lower anthropogenic origin such as stationary source or vehicular traffic and showed a character of the rural site.

PM2.5 source apportionment was characterized by positive matrix factorization (PMF) analysis, and the results inferred four major sources: sea salt (10.2%), biomass combustion (18.9%), soil dust (13.2%) and secondary aerosol (44.4%). The potential source contribution function (PSCF) analysis suggested that the major sources of secondary aerosol and sea salts were domestic in southwest Japan and the Sea of Japan, whereas the sources of biomass combustion and soil dust in specific seasons were transported long distance from the Northeast Asian continent (NEA).

Comparing with previous studies in western Japan, this study showed a large domestic contribution of southwest Japan for secondary aerosol, while a larger contribution of the NEA was observed in the previous studies. The significant contribution of biomass combustion from northeast China in autumn, and local area in Niigata and southwest Japan in the other seasons were uniquely observed in this study.

This work was partly supported by JSPS KAKENHI Grant Number 25502005 and Environment Research and Technology Development Fund (5-1306) of the Ministry of the Environment, Japan.

The paper on this study is as follows: Li et al. 2018. Chemical Characteristics and Source Apportionment of PM2.5 and Long-range Transport from Northeast Asia Continent to Niigata in Eastern Japan.
Aerosol and Air Quality Research, 18: 938–956.
http://www.aaqr.org/files/article/6596/9_AAQR-17-05-OA-0181_938-956.pdf

Catchment Studies in Kajikawa Study Site and Lake Ijira Monitoring Site

Recent Major Research Achievements

<Response of river water chemistry to changing the atmospheric environment and sulfur dynamics in a forested catchment in central Japan>

The Lake Ijira catchment (IJR) is located in the downwind region of the Chukyo Industrial Area in central Japan and has historically experienced large-scale deposition of S and nitrogen (N) from the atmosphere. Previous studies have suggested that IJR was acidified and N-saturated, which was triggered by climatic anomalies (cold summer and drought summer) in the mid-1990s. Long-term monitoring data on the river water (RW) chemistry since 1988 were assessed with intensive survey datasets on the input–output material budgets and S isotopic analysis (δ34S).

With a decline in NO3- concentrations, RW pH recovered to its original level, around 7.0, in the early 2000s. Reductions in atmospheric deposition, diminished effects of climatic anomalies, and forest management practices (such as thinning), have all contributed to RW chemistry recovery.

Although the SO42- output significantly exceeded the input, the δ34S analysis showed that geological (rock) S largely contributed (estimated as 75-91%) to the discrepancy of the input–output budget. On the other hand, atmospheric S appeared to accumulate in the soil as organic S. The tree-ring δ34S profile recorded historical changes in the atmospheric inputs in the Chukyo region.

RW chemistry has sensitively responded to changes in the atmospheric environment, including the atmospheric deposition of S and N and climatic anomalies, and as future changes are likely, long-term monitoring is essential.

This study was conducted using monitoring data obtained from the MOEJ and the related research outputs. Sulfur isotopic analysis of tree disks was conducted with the support of the Joint Research Grant for the Environmental Isotope Study of Research Institute for Humanity and Nature.

The paper on this study is as follows:
Sase H et al. 2019. Response of river water chemistry to changing atmospheric environment and sulfur dynamics in a forested catchment in central Japan.
Biogeochemistry, 142, 357–374.
https://doi.org/10.1007/s10533-019-00540-1

<Export flux of unprocessed atmospheric nitrate from temperate forested catchments: a possible new index for nitrogen saturation>

Based on the collaborative studies with Associate Prof. Fumiko Nakawaga and Prof. Urumu Tsunogai, Nagoya University, the paper on triple oxygen isotopic analysis of nitrate (NO3-), which utilized monitoring samples from Kajikawa study site and Lake Ijira catchment, was published in Biogeosciences on 22 November 2018.

To clarify the biological processing of nitrate within temperate forested catchments using unprocessed atmospheric nitrate exported from each catchment as a tracer, we continuously monitored stream nitrate concentrations and stable isotopic compositions, including 17O excess (Δ17O), in three forested catchments in Kajikawa study site (KJ) and Lake Ijira catchment (IJ1 and IJ2) for more than 2 years.

The estimated annual export flux of unprocessed atmospheric nitrate accounted for 9.4% ± 2.6 %, 6.5% ± 1.8 %, and 2.6%± 0.6% of the annual deposition flux of atmospheric nitrate in KJ, IJ1, and IJ2, respectively. The export flux of unprocessed atmospheric nitrate relative to the deposition flux showed a clear normal correlation with the flux-weighted average concentration of stream nitrate, indicating that reductions in the biological assimilation rates of nitrate in forested soils, rather than increased nitrification rates, are likely responsible for the elevated stream nitrate concentration, probably as a result of nitrogen saturation. The export flux of unprocessed atmospheric nitrate relative to the deposition flux in each forest ecosystem is applicable as an index for nitrogen saturation.

The samples analyzed in this study were collected through the Long-term Monitoring of Transboundary Air Pollution and Acid Deposition by the Ministry of the Environment in Japan. This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science, and Technology of Japan under grant numbers,15H02804, 16K14308, 15K12187, 17H00780, 26241006, and 24651002.

The paper on this study is as follows:
Nakagawa F et al. 2018. Export flux of unprocessed atmospheric nitrate from temperate forested catchments: a possible new index for nitrogen saturation.
Biogeosciences, 15, 7025-7042.
https://www.biogeosciences.net/15/7025/2018/

Joint Research Projects with EANET participating countries

Recent Major Research Achievements

<Alkalinization and acidification of stream water with changes in atmospheric deposition in a tropical dry evergreen forest of northeastern Thailand>

The climate in northeastern Thailand is classified as a tropical savanna climate with distinct dry and wet seasons. In accordance with the climate, seasonality of water/material inputs from the atmosphere may largely affect biogeochemical processes in terrestrial ecosystems. In this study, field surveys on atmospheric deposition and stream water chemistry were conducted over 6 years in an evergreen forest of Sakaerat site in northeastern Thailand.

Atmospheric deposition of ion constituents by throughfall and stemflow was shown to increase in the beginning and end of the wet season, reflecting the precipitation pattern. The pH and electrical conductivity of stream water increased with alkalinity and base cation concentrations (alkalinization) due to mineralization of organic matter by the first rain and retention of anions in the soil during the start of the wet season.

After initial alkalinization, the pH and alkalinity declined rapidly with the highest SO42- concentration displayed in the middle towards the end of the wet season (acidification). The magnitude of peaks in SO42- concentration reflects deposition during the first 2 months of the wet season (March and April) in respective years. Release of SO42- with H+, which is retained in the soil during the early wet season, may cause acidification later in the season.

The deposition and concentration of SO42- declined over 6 years. However, the pH of stream water declined with increasing concentrations of SO42- and other major ions. The release of materials accumulated in the ecosystem was facilitated by the decrease in SO42- concentration/deposition and increased precipitation in the middle–late wet season.

The retention‐release cycle of SO42- largely contributed to both seasonal and inter annual variations in stream water chemistry in the tropical savanna climate studied

The study was supported financially by a Grant‐in‐Aid for Scientific Research on Innovative Areas (20120012) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan; the Environment Research and Technology Development Fund (C‐052, C‐082 and B‐0801) from the Ministry of the Environment of Japan; and a grant from the Asia‐Pacific Network for Global Change Research (APN, ARCP2012‐18NMY‐Sase; ARCP2013‐13CMY‐Sase, Sase et al., 2015).

The paper on this study is as follows: Sase H et al. 2017. Alkalinization and acidification of stream water with changes in atmospheric deposition in a tropical dry evergreen forest of northeastern Thailand. Hydrological Processes, 31, 836–846. https://onlinelibrary.wiley.com/doi/abs/10.1002/hyp.11062