Detectability of the potential climate change effect on transboundary air pollution pathways in the downwind area of China.

Long-term aerosol optical depth (AOD) datasets focused on the Pacific Ocean in the downwind area of China over a 19-year period from 2003 to 2021 were derived from satellite observations, reanalysis datasets, and numerical simulations. Considering the significant year-to-year changes in the amounts of aerosols transported from China to the Pacific Ocean during this period, we proposed a metric named R. This is defined as the AOD over the ocean relative to that near the eastern coast of China within the same latitude band (25-30°N).

Severe level of photochemical oxidants (O) over the western coast of Japan during autumn after typhoon passing.

Photochemical oxidants (O; mainly O) are a concern in East Asia. Because of the prevailing westerly wind in the midlatitudes, O concentration generally shows a high in spring over Kyushu Island, western Japan, and O warnings have been issued in spring. However, the record from 2000 to 2021 of O warning days in Kyushu Island contains one warning case in autumn 2020.

Effectiveness of emission controls implemented since 2000 on ambient ozone concentrations in multiple timescales in Japan: An emission inventory development and simulation study.

It has been reported that ambient ozone concentrations in Japan have not been effectively suppressed by precursor emission controls. In this study, we developed an unprecedented long-term emission inventory of ozone precursors, including nitrogen oxide (NO) and volatile organic compounds (VOCs), in Japan. The developed emission inventory, which explicitly represents changes in emissions caused by emission controls and variation in activities from 2000 to 2019, revealed that emission controls implemented for vehicles, large point sources, and fugitive VOC sources effectively reduced precursor emissions.

How have Divergent Global Emission Trends Influenced Long-range Transported Ozone to North America?

Several locations across the United States in non-compliance with the national standard for ground-level ozone (O) are thought to have sizeable influences from distant extra-regional emission sources or natural stratospheric O, which complicates design of local emission control measures. To quantify the amount of long-range transported O (LRT O), its origin, and change over time, we conduct and analyze detailed sensitivity calculations characterizing the response of O to emissions from different source regions across the Northern Hemisphere in conjunction with multi-decadal simulations of tropospheric O distributions and changes. Model calculations show that the amount of O at any location attributable to sources outside North America varies both spatially and seasonally.

Role of Dust and Iron Solubility in Sulfate Formation during the Long-Range Transport in East Asia Evidenced by O-Excess Signatures.

Numerical models have been developed to elucidate air pollution caused by sulfate aerosols (SO). However, typical models generally underestimate SO, and oxidation processes have not been validated. This study improves the modeling of SO formation processes using the mass-independent oxygen isotopic composition [O-excess; ΔO(SO)], which reflects pathways from sulfur dioxide (SO) to SO, at the background site in Japan throughout 2015.

Quantifying the wet deposition of reactive nitrogen over China: Synthesis of observations and models.

Accurate estimation on reaction nitrogen (N) deposition is highly demanded for assessing the impacts on the environment and human beings. This study investigated the wet deposition of inorganic nitrogen (IN) in mainland China by measurements from over 500 sites from five observational networks/databases and ensemble results of eleven chemical transport models (CTMs). Each data source has its focus and limitations and together formed a comprehensive view over China.

Returning long-range PM transport into the leeward of East Asia in 2021 after Chinese economic recovery from the COVID-19 pandemic.

Changes in the aerosol composition of sulfate (SO) and nitrate (NO) from 2012 to 2019 have been captured as a paradigm shift in the region downwind of China. Specifically, SO dramatically decreased and NO dramatically increased over downwind locations such as western Japan due to the faster reduction of SO emissions than NO emissions and the almost constant trend of NH emissions from China. Emissions from China sharply decreased during COVID-19 lockdowns in February-March 2020, after which China's economic situation seemed to recover going into 2021.

Incorporation of volcanic SO emissions in the Hemispheric CMAQ (H-CMAQ) version 5.2 modeling system and assessing their impacts on sulfate aerosol over the Northern Hemisphere.

The state-of-the-science Community Multiscale Air Quality (CMAQ) Modeling System has recently been extended for hemispheric-scale modeling applications (referred to as H-CMAQ). In this study, satellite-constrained estimation of the degassing SO emissions from 50 volcanoes over the Northern Hemisphere is incorporated into H-CMAQ, and their impact on tropospheric sulfate aerosol ( ) levels is assessed for 2010. The volcanic degassing improves predictions of observations from the Acid Deposition Monitoring Network in East Asia (EANET), the United States Clean Air Status and Trends Network (CASTNET), and the United States Integrated Monitoring of Protected Visual Environments (IMPROVE).

Improving Estimates of Sulfur, Nitrogen, and Ozone Total Deposition through Multi-Model and Measurement-Model Fusion Approaches.

Earth system and environmental impact studies need high quality and up-to-date estimates of atmospheric deposition. This study demonstrates the methodological benefits of multimodel ensemble and measurement-model fusion mapping approaches for atmospheric deposition focusing on 2010, a year for which several studies were conducted. Global model-only deposition assessment can be further improved by integrating new model-measurement techniques, including expanded capabilities of satellite observations of atmospheric composition.

Disentangling the contribution of the transboundary out-flow from the Asian continent to Tokyo, Japan.

We assessed the contribution of transboundary air pollutants (TAPs) transported from China to Tokyo using the Pb/Cu index. We conducted intensive observations over four seasons during 2014-2015 and analyzed ionic components and thirteen elements in size-segregated aerosols collected at the top of a 30-m-high tower in a hilly forested area of the Field Museum Tamakyuryo (FM Tama), in a western suburb of Tokyo. In order to evaluate if the Pb/Cu ratio can be applied in Tokyo as the megacity, the annual average concentration of Pb at Cape Hedo, Kumamoto city, on the west side of Japan, was higher than that of Pb at Tokyo, on the east side; this result indicates that TAPs affect western Japan more than eastern Japan.

Trends of sulfur and nitrogen deposition from 2003 to 2017 in Japanese remote areas.

Emissions of sulfur (S) and nitrogen (N) compounds in East Asia has drastically changed over the last two decades. To assess the influence of the drastic changes in air pollution on ecosystems in Japan, we investigated the trends of S and N deposition during 2003-2017 at remote sites of Acid Deposition Monitoring Network in East Asia (EANET). We measured wet deposition and inferentially estimated dry deposition of S and N using monitoring data from 2003 to 2017 at eight sites.

Nitrogen burden from atmospheric deposition in East Asian oceans in 2010 based on high-resolution regional numerical modeling.

East Asian oceans are possibly affected by a high nitrogen (N) burden because of the intense anthropogenic emissions in this region. Based on high-resolution regional chemical transport modeling with horizontal grid scales of 36 and 12 km, we investigated the N burden into East Asian oceans via atmospheric deposition in 2010. We found a high N burden of 2-9 kg N ha yr over the Yellow Sea, East China Sea (ECS), and Sea of Japan.

Impacts of COVID-19 lockdown, Spring Festival and meteorology on the NO variations in early 2020 over China based on in-situ observations, satellite retrievals and model simulations.

The lockdown measures due to COVID-19 affected the industry, transportation and other human activities within China in early 2020, and subsequently the emissions of air pollutants. The decrease of atmospheric NO due to the COVID-19 lockdown and other factors were quantitively analyzed based on the surface concentrations by in-situ observations, the tropospheric vertical column densities (VCDs) by different satellite retrievals including OMI and TROPOMI, and the model simulations by GEOS-Chem. The results indicated that due to the COVID-19 lockdown, the surface NO concentrations decreased by 42% ± 8% and 26% ± 9% over China in February and March 2020, respectively.

Modeling stratospheric intrusion and trans-Pacific transport on tropospheric ozone using hemispheric CMAQ during April 2010 - Part 2: Examination of emission impacts based on the higher-order decoupled direct method.

The state-of-the-science Community Multiscale Air Quality (CMAQ) modeling system, which has recently been extended for hemispheric-scale modeling applications (referred to as H-CMAQ), is applied to study the trans-Pacific transport, a phenomenon recognized as a potential source of air pollution in the US, during April 2010. The results of this analysis are presented in two parts. In the previous paper (Part 1), model evaluation for tropospheric ozone (O) was presented and an air mass characterization method was developed.

Modeling stratospheric intrusion and trans-Pacific transport on tropospheric ozone using hemispheric CMAQ during April 2010 - Part 1: Model evaluation and air mass characterization for stratosphere-troposphere transport.

Stratospheric intrusion and trans-Pacific transport have been recognized as a potential source of tropospheric ozone over the US. The state-of-the-science Community Multiscale Air Quality (CMAQ) modeling system has recently been extended for hemispheric-scale modeling applications (referred to as H-CMAQ). In this study, H-CMAQ is applied to study the stratospheric intrusion and trans-Pacific transport during April 2010.

Paradigm shift in aerosol chemical composition over regions downwind of China.

A rapid decrease in PM concentrations in China has been observed in response to the enactment of strong emission control policies. From 2012 to 2017, total emissions of SO and NO from China decreased by approximately 63% and 24%, respectively. Simultaneously, decreases in the PM concentration in Japan have been observed since 2014, and the proportion of stations that satisfy the PM environmental standard (daily, 35 µg/m; annual average, 15 µg/m) increased from 37.

Chinese province-scale source apportionments for sulfate aerosol in 2005 evaluated by the tagged tracer method.

Appropriate policies to improve air quality by reducing anthropogenic emissions are urgently needed. This is typified by the particulate matter (PM) problem and it is well known that one type of PM, sulfate aerosol (SO), has a large-scale impact due to long range transport. In this study we evaluate the source-receptor relationships of SO over East Asia for 2005, when anthropogenic sulfur dioxide (SO) emissions from China peaked.

Long-term inverse modeling of Chinese CO emission from satellite observations.

Carbon monoxide (CO) emissions in China in 2005-2010 were estimated by inversion, using the Green's function method from vertical CO profiles derived from MOPITT Version 5 satellite data and a tagged CO simulation, and validated with independent in situ observations from the World Data Centre for Greenhouse Gases. Modeling with a posteriori emission successfully reproduced CO outflow from the continent to the East China Sea, Sea of Japan, and Japanese islands during winter and spring, and compensated for underestimates in central and eastern China in summer. A posteriori emissions showed large seasonal variations in which December and March emissions were on average 23% larger than August emissions, consistent with other studies.

Source contributions of sulfate aerosol over East Asia estimated by CMAQ-DDM.

We applied the decoupled direct method (DDM), a sensitivity analysis technique for computing sensitivities accurately and efficiently, to determine the source-receptor relationships of anthropogenic SO(2) emissions to sulfate aerosol over East Asia. We assessed source contributions from East Asia being transported to Oki Island downwind from China and Korea during two air pollution episodes that occurred in July 2005. The contribution from China, particularly that from central eastern China (CEC), was found to dominate the sulfate aerosols.