Search

The impact of ambient air pollution on human health, particularly fine particulate matter (PM2.5) and tropospheric ozone (O3), is a critical global concern. Atmospheric chemical transport models (CTMs) are widely used to predict air pollutant concentrations and assess associated health risks. However, there is a need to better understand how the horizontal resolution of these models influences their accuracy, especially in future assessments. In this study, we compared the performance of global low-resolution CTMs with high-resolution nested simulations for estimating O3 and PM2.5 concentrations. The models were validated against observational data to determine their accuracy across different spatial scales and to evaluate their suitability for future scenario assessments. Our findings demonstrate that while the nested-grid simulations improved the reproducibility of regional observations, especially in areas with complex topography or localized emissions, the overall global-scale performance of the model did not significantly benefit from higher resolution. Additionally, the differences in global health and agricultural impacts between low- and high-resolution simulations were minor and within the range of uncertainty typically associated with emission inventories and CTMs. However, for specific regional studies or policy applications, higher resolution may offer improved accuracy. Ultimately, the current low-spatial-resolution model provides sufficient accuracy for many global-scale applications, but the choice of resolution should be carefully considered depending on the specific objectives of the study especially in future scenario.

Abstract: Atmospheric deposition of dust aerosols is a significant source of exogenous iron (Fe) in marine ecosystems and is critical in setting primary marine productivity during summer. This dust‐borne input of Fe is particularly important to the Southern Ocean, which is arguably the most biogeochemically important ocean because of its large spatial extent and its considerable influence on the global carbon cycle. However, there is large uncertainty in estimates of dust emissions in the Southern Hemisphere and thus of the deposition of Fe‐containing aerosols onto oceans. Here we hypothesize that sparsely vegetated surfaces in arid and semiarid regions are important sources of Fe‐containing aerosols to the Southern Ocean. We test this hypothesis using an improved dust emission scheme in conjunction with satellite products of vegetation cover and soil moisture in an atmospheric chemistry transport model. Our improved model shows a twofold increase of Fe input into the Southern Ocean in austral summer with respect to spring and estimates that the Fe input is more than double that simulated using a conventional dust emission scheme in summer. Our model results suggest that dust emissions from open shrublands contribute over 90% of total Fe deposition into the Southern Ocean. These findings have important implications for the projection of the Southern Ocean's carbon uptake.

Abstract The measurements of one of the major greenhouse gases, carbon dioxide (CO2), are being made using dedicated satellite remote sensing since the launch of the greenhouse gases observing satellite (GOSAT) by a three-way partnership between the Japan Aerospace Exploration Agency (JAXA), the Ministry of Environment (MoE) and the National Institute for Environmental Studies (NIES), and the National Aeronautics and Space Administration (NASA) Orbiting Carbon Observatory-2 (OCO-2). In the past 10 years, estimation of CO2 fluxes from land and ocean using the earth system models (ESMs) and inverse modelling of in situ atmospheric CO2 data have also made significant progress. We attempt, for the first time, to evaluate the CO2 fluxes simulated by an earth system model (MIROC-ES2L) and the fluxes estimated by an inverse model (MIROC4-Inv) using in situ data by comparing with GOSAT and OCO-2 observations. Both MIROC-ES2L and MIROC4-Inv fluxes are used in the MIROC4-atmospheric chemistry transport model (referred to as ACTM_ES2LF and ACTM_InvF, respectively) for calculating total column CO2 mole fraction (XCO2) that are sampled at the time and location of the satellite measurements. Both the ACTM simulations agreed well with the GOSAT and OCO-2 satellite observations, within 2 ppm for the spatial maps and time evolutions of the zonal mean distributions. Our results suggest that the inverse model using in situ data is more consistent with the OCO-2 retrievals, compared with those of the GOSAT XCO2 data due to the higher accuracy of the former. This suggests that the MIROC4-Inv fluxes are of sufficient quality to evaluate MIROC-ES2L simulated fluxes. The ACTM_ES2LF simulation shows a slightly weaker seasonal cycle for the meridional profiles of CO2 fluxes, compared with that from the ACTM_InvF. This difference is revealed by greater XCO2 differences for ACTM_ES2LF vs GOSAT, compared with those of ACTM_InvF vs GOSAT. Using remote sensing–based global products of leaf area index (LAI) and gross primary productivity (GPP) over land, we show a weaker sensitivity of MIROC-ES2L biospheric activities to the weather and climate in the tropical regions. Our results clearly suggest the usefulness of XCO2 measurements by satellite remote sensing for evaluation of large-scale ESMs, which so far remained untested by the sparse in situ data.

As one of the regions with intensive agriculture and rapid economic development in China, North China also has a high nitrogen (N) deposition. This study characterized the spatial pattern of N deposition in North China, combining the tropospheric columns from satellite measurements and the simulated profiles from an atmospheric chemistry transport model. The total N deposition fluxes ranged from 16.3 to 106.5 kg N ha−1 yr−1, with an average of 54.5 ± 17.2 kg N ha−1 yr−1. The high values were concentrated in urban and farmland areas, while low values were found in forests and grasslands with less human activities. Of the total N deposition, 36% was deposited via precipitation, 12% was deposited through dry particulate deposition, and the remaining 52% was comprised of dry gaseous deposition. For the seasonal variation of dry deposition, gaseous HNO3 and particulate NO3− were higher in winter and autumn, but lower in spring and summer. In contrast, gaseous NH3 and particulate NH4+ were higher in spring and summer, but lower in winter and autumn. This is possibly caused by the seasonal differences in emission intensity between NOx and NH3 emission sources. The gaseous NO2 deposition did not show strong seasonal variation. The wet deposition was mainly affected by precipitation, with high values in summer and low values in winter. This research provides an objective spatial perspective and insight into the total N deposition in North China.

The measurements of one of the major greenhouse gases, carbon dioxide (CO2), are being made using dedicated satellite remote sensing since the launch of the greenhouse gases observing satellite (GOSAT) by a three-way partnership between the Japan Aerospace Exploration Agency (JAXA), the Ministry of Environment (MoE) and the National Institute for Environmental Studies (NIES), and the National Aeronautics and Space Administration (NASA) Orbiting Carbon Observatory-2 (OCO-2). In the past 10 years, estimation of CO2 fluxes from land and ocean using the earth system models (ESMs) and inverse modelling of in situ atmospheric CO2 data have also made significant progress. We attempt, for the first time, to evaluate the CO2 fluxes simulated by an earth system model (MIROC-ES2L) and the fluxes estimated by an inverse model (MIROC4-Inv) using in situ data by comparing with GOSAT and OCO-2 observations. Both MIROC-ES2L and MIROC4-Inv fluxes are used in the MIROC4-atmospheric chemistry transport model (referred to as ACTM_ES2LF and ACTM_InvF, respectively) for calculating total column CO2 mole fraction (XCO2) that are sampled at the time and location of the satellite measurements. Both the ACTM simulations agreed well with the GOSAT and OCO-2 satellite observations, within 2 ppm for the spatial maps and time evolutions of the zonal mean distributions. Our results suggest that the inverse model using in situ data is more consistent with the OCO-2 retrievals, compared with those of the GOSAT XCO2 data due to the higher accuracy of the former. This suggests that the MIROC4-Inv fluxes are of sufficient quality to evaluate MIROC-ES2L simulated fluxes. The ACTM_ES2LF simulation shows a slightly weaker seasonal cycle for the meridional profiles of CO2 fluxes, compared with that from the ACTM_InvF. This difference is revealed by greater XCO2 differences for ACTM_ES2LF vs GOSAT, compared with those of ACTM_InvF vs GOSAT. Using remote sensing–based global products of leaf area index (LAI) and gross primary productivity (GPP) over land, we show a weaker sensitivity of MIROC-ES2L biospheric activities to the weather and climate in the tropical regions. Our results clearly suggest the usefulness of XCO2 measurements by satellite remote sensing for evaluation of large-scale ESMs, which so far remained untested by the sparse in situ data. [ABSTRACT FROM AUTHOR]

We present observations of CH4 concentrations from the lower to upper troposphere (LT and UT) over Japan during 1988–2010 based on aircraft measurements from the Tohoku University (TU). The analysis is aided by simulation results using an atmospheric chemistry transport model (i.e. ACTM). Tropospheric CH4 over Japan shows interannual and seasonal variations that are dependent on altitudes, primarily reflecting differences in air mass origins at different altitudes. The long-term trend and interannual variation of CH4 in the LT are consistent with previous reports of measurements at surface baseline stations in the northern hemisphere. However, those in the UT show slightly different features from those in the LT. In the UT, CH4 concentrations show a seasonal maximum in August due to efficient transport of air masses influenced by continental CH4 sources, while LT CH4 reaches its seasonal minimum during summer due to enhanced chemical loss. Vertical profiles of the CH4 concentrations also vary with season, reflecting the seasonal cycles at the respective altitudes. In summer, transport of CH4-rich air from Asian regions elevates UT CH4 levels, forming a uniform vertical profile above the mid-troposphere. On the other hand, CH4 decreases nearly monotonically with altitude in winter–spring. The ACTM simulations with different emission scenarios reproduce general features of the tropospheric CH4 variations over Japan. Tagged tracer simulations using the ACTM indicate substantial contributions of CH4 sources in South Asia and East Asia to the summertime high CH4 values observed in the UT. This suggests that our observations over Japan are highly sensitive to CH4 emission signals particularly from Asia.

The NO 2 dry deposition over China was estimated based on an inferential model, in which the surface NO 2 concentrations and deposition velocities were derived from OMI columnar NO 2 and the simulation results from atmospheric chemistry transport models. Nationally, the annual NO 2 dry deposition fluxes ranged from 0.0005 to 8.54 kg N ha −1 , with an average of 0.48 kg N ha −1 . The total NO 2 dry deposition over China was 0.46 Tg N yr −1 , mainly contributed by northern and southeast China. Due to contrary seasonal trends of the NO 2 concentrations (high in cold months) and deposition velocities (high in warm months), the estimated NO 2 dry depositions did not show strong seasonal pattern, instead showing relatively high values from August to October and low ones in February. The annual NO 2 dry deposition has an increasing trend from 2007 to 2014, with the highest deposition level achieved in 2011. This research conducts a thorough validation between estimated NO 2 dry depositions with ground measurements of NO 2 concentrations and provides an objective spatial perspective and insight on the existing NO 2 dry deposition maps in China. [ABSTRACT FROM AUTHOR]

A period of elevated surface concentrations of airborne particulate matter (PM) in the UK in spring 2014 was widely associated in the UK media with a Saharan dust plume. This might have led to over-emphasis on a natural phenomenon and consequently to a missed opportunity to inform the public and provide robust evidence for policy-makers about the observed characteristics and causes of this pollution event. In this work, the EMEP4UK regional atmospheric chemistry transport model (ACTM) was used in conjunction with speciated PM measurements to investigate the sources and long-range transport (including vertical) processes contributing to the chemical components of the elevated surface PM. It is shown that the elevated PM during this period was mainly driven by ammonium nitrate, much of which was derived from emissions outside the UK. In the early part of the episode, Saharan dust remained aloft above the UK; we show that a significant contribution of Saharan dust at surface level was restricted only to the latter part of the elevated PM period and to a relatively small geographic area in the southern part of the UK. The analyses presented in this paper illustrate the capability of advanced ACTMs, corroborated with chemically-speciated measurements, to identify the underlying causes of complex PM air pollution episodes. Specifically, the analyses highlight the substantial contribution of secondary inorganic ammonium nitrate PM, with agricultural ammonia emissions in continental Europe presenting a major driver. The findings suggest that more emphasis on reducing emissions in Europe would have marked benefits in reducing episodic PM _2.5 concentrations in the UK.

We present observations of CH4 concentrations from the lower to upper troposphere (LT and UT) over Japan during 1988-2010 based on aircraft measurements from the Tohoku University (TU). The analysis is aided by simulation results using an atmospheric chemistry transport model (i.e. ACTM). Tropospheric CH4 over Japan shows interannual and seasonal variations that are dependent on altitudes, primarily reflecting differences in air mass origins at different altitudes. The long-term trend and interannual variation of CH4 in the LT are consistent with previous reports of measurements at surface baseline stations in the northern hemisphere. However, those in the UT show slightly different features from those in the LT. In the UT, CH4 concentrations show a seasonal maximum in August due to efficient transport of air masses influenced by continental CH4 sources, while LT CH4 reaches its seasonal minimum during summer due to enhanced chemical loss. Vertical profiles of the CH4 concentrations also vary with season, reflecting the seasonal cycles at the respective altitudes. In summer, transport of CH4-rich air from Asian regions elevates UT CH4 levels, forming a uniform vertical profile above the mid-troposphere. On the other hand, CH4 decreases nearly monotonically with altitude in winter-spring. The ACTM simulations with different emission scenarios reproduce general features of the tropospheric CH4 variations over Japan. Tagged tracer simulations using the ACTM indicate substantial contributions of CH4 sources in South Asia and East Asia to the summertime high CH4 values observed in the UT. This suggests that our observations over Japan are highly sensitive to CH4 emission signals particularly from Asia. [ABSTRACT FROM AUTHOR]