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Abstract We developed a near-real-time estimation method for temporal changes in fossil fuel CO2 (FFCO2) emissions from China for 3 months [January, February, March (JFM)] based on atmospheric CO2 and CH4 observations on Hateruma Island (HAT, 24.06° N, 123.81° E) and Yonaguni Island (YON, 24.47° N, 123.01° E), Japan. These two remote islands are in the downwind region of continental East Asia during winter because of the East Asian monsoon. Previous studies have revealed that monthly averages of synoptic-scale variability ratios of atmospheric CO2 and CH4 (ΔCO2/ΔCH4) observed at HAT and YON in JFM are sensitive to changes in continental emissions. From the analysis based on an atmospheric transport model with all components of CO2 and CH4 fluxes, we found that the ΔCO2/ΔCH4 ratio was linearly related to the FFCO2/CH4 emission ratio in China because calculating the variability ratio canceled out the transport influences. Using the simulated linear relationship, we converted the observed ΔCO2/ΔCH4 ratios into FFCO2/CH4 emission ratios in China. The change rates of the emission ratios for 2020–2022 were calculated relative to those for the preceding 9-year period (2011–2019), during which relatively stable ΔCO2/ΔCH4 ratios were observed. These changes in the emission ratios can be read as FFCO2 emission changes under the assumption of no interannual variations in CH4 emissions and biospheric CO2 fluxes for JFM. The resulting average changes in the FFCO2 emissions in January, February, and March 2020 were 17 ± 8%, − 36 ± 7%, and − 12 ± 8%, respectively, (− 10 ± 9% for JFM overall) relative to 2011–2019. These results were generally consistent with previous estimates. The emission changes for January, February, and March were 18 ± 8%, − 2 ± 10%, and 29 ± 12%, respectively, in 2021 (15 ± 10% for JFM overall) and 20 ± 9%, − 3 ± 10%, and − 10 ± 9%, respectively, in 2022 (2 ± 9% for JFM overall). These results suggest that the FFCO2 emissions from China rebounded to the normal level or set a new high record in early 2021 after a reduction during the COVID-19 lockdown. In addition, the estimated reduction in March 2022 might be attributed to the influence of a new wave of COVID-19 infections in Shanghai.

Abstract The dramatic increase of natural gas use in China, as a substitute for coal, helps to reduce CO2 emissions and air pollution, but the climate mitigation benefit can be offset by methane leakage into the atmosphere. We estimate methane emissions from 2010 to 2018 in four regions of China using the GOSAT satellite data and in-situ observations with a high-resolution (0.1° × 0.1°) inverse model and analyze interannual changes of emissions by source sectors. We find that estimated methane emission over the north-eastern China region contributes the largest part (0.77 Tg CH4 yr−1) of the methane emission growth rate of China (0.87 Tg CH4 yr−1) and is largely attributable to the growth in natural gas use. The results provide evidence of a detectable impact on atmospheric methane observations by the increasing natural gas use in China and call for methane emission reductions throughout the gas supply chain and promotion of low emission end-use facilities.

Quantifying emissions from megacities is important for reduction of greenhouse gases. We used atmospheric carbon dioxide (CO2) concentration data obtained at an altitude of around 250 m above the ground on TOKYO SKYTREE (TST; a 634-m-high freestanding broadcasting tower; 35.71°N, 139.81°E), which is located north of central Tokyo, Japan. To use the TST observations for estimating net CO2 fluxes from Tokyo, a global, high-resolution simulation of atmospheric CO2 transport with CO2 flux data from a global inverse analysis was performed. In the simulation, atmospheric CO2 variations were well reproduced at remote sites around Japan. The application of tagged tracers in the simulation revealed that variations of CO2 concentrations at TST were largely driven by fluxes in the southwest region of Tokyo, including the western Tokyo Bay area where huge power plants are located. Then, we performed a regression analysis of modeled and observed Tokyo-originated CO2 concentrations, both of which were derived from the simulated background concentrations, while changing the minimum wind speed used in the analysis. The removal of low wind speeds altered the slope of the regression line, and excluding wind speeds below 7 m s−1 resulted in a stabilized slope of 0.93 ± 0.08. This stabilized regression indicated that the annual net CO2 emission from Tokyo is 79.5 ± 6.6 Tg-C yr−1. Our findings demonstrate that analysis using a global high-resolution model with tagged tracers has the potential to monitor emissions changes in a megacity. [ABSTRACT FROM AUTHOR]

Atmospheric carbonyl sulfide (COS) has received increasing attention as a potential tracer for investigating the global carbon cycle. Owing to the irreversible photosynthetic absorption of COS, changes in the atmospheric COS mole fraction can be related to terrestrial gross primary production. However, the instability of COS in high-pressure cylinders has hampered the accurate determination of atmospheric COS. Here, we report a dynamic dilution method for generating reference gas mixtures containing COS at ambient levels (ca. 500 pmol mol-1). Our method combined a dynamic dilution system employing a high-accuracy mass flow measurement system and a gravimetrically prepared parent gas mixture containing a micromole-per-mole level of COS filled in a high-pressure aluminium cylinder, the COS stability of which we experimentally validated for at least 10 years. We evaluated the dilution performance of the developed method using a gravimetric parent gas mixture containing approximately 1 μmol mol-1 of COS and chlorodifluoromethane (HCFC-22). In our evaluation experiments, excellent repeatability (0.23 % for COS and 0.43 % for HCFC-22 in terms of relative standard deviation), reproducibility (COS: 0.04 %, HCFC-22: 0.28 %), and dilution linearity (R² > 0.99, for both COS and HCFC-22) were obtained. The dilution accuracy was examined by comparing the determined HCFC-22 mole fractions in a dynamically diluted parent gas mixture from a mass flow rate measurement system and gas chromatography-mass spectrometry (GC/MS) calibrated using a gravimetrically diluted parent gas mixture. The mole fractions of HCFC-22 from these two methods agreed within an acceptable difference of approximately 2 pmol mol-1, validating the dilution accuracy of the developed method. By re-evaluating the experimental data, we determined the mole fractions of COS and HCFC-22 in an ambient air-based reference gas mixture, with relative standard errors of 0.02 % for COS and 0.12 % for HCFC-22. These results demonstrated that the developed method can accurately generate reference gas mixtures containing COS at ambient levels, which we expect will support long-term observations of atmospheric COS. [ABSTRACT FROM AUTHOR]

The island of Hateruma is the southernmost inhabited island of Japan. Here we interpret observations of carbon monoxide (CO), ethane (C2H6), propane (C3H8), nitrogen oxides (NOx and NOy) and ozone (O3) made from the island in 2018 with the GEOS-Chem atmospheric chemistry transport model. We simulated the concentrations of these species within a nested grid centered over the site, with a model resolution of 0.5°×0.625°. We use the Community Emissions Data System (CEDS) emissions dataset for anthropogenic emissions and add a geological source of C2H6 and C3H8. The model captured the seasonality of primary pollutants (CO, C2H6, C3H8) at the site - high concentrations in the winter months when oxidation rates are low and flow is from the north, and low concentrations in the summer months when oxidation rates are higher and flow is from the south. It also simulates many of the synoptic scale events with Pearson’s correlation coefficients (r) of 0.74, 0.88 and 0.89 for CO, C2H6 and C3H8, respectively. Concentrations of CO are well simulated by the model (with a gradient of best fit between model and measurements of 0.91) but simulated concentrations of C2H6 and C3H8 are significantly lower than the observations (gradients of best fit between model and measurement of 0.57 and 0.41, respectively), most noticeably in the winter months. Simulated NOx concentrations were underestimated but NOy appear to be overestimated. The concentration of O3 is moderately well simulated (gradient of best fit line of 0.76, with an r of 0.87) but there is a tendency to underestimate concentrations in the winter months. By switching off the model’s biomass burning emissions we show that during winter biomass burning has limited influence on the concentration of compounds in the winter but can represent a sizeable fraction in the summer. We also show that increasing the anthropogenic emissions of C2H6 and C3H8 in Asia by factors of 2.22 and 3.17, respectively, significantly increases the model’s ability to simulate these species in the winter months, consistent with previous studies. [ABSTRACT FROM AUTHOR]

Synoptic-scale variabilities of atmospheric CO2 and CH4 observed at Yonagunijima (Yonaguni Island, YON, 24.47°N, 123.01°E) during winter (from January to March) in 1998 - 2020 were examined. The monthly mean variability ratios (ΔCO2/ΔCH4) based on correlation slopes within 24 h time windows showed a clear increasing trend, which is mainly attributed to the unprecedented increase in the fossil fuel-derived CO2 (FFCO2) emissions from China. A similar increasing trend of the ΔCO2/ΔCH4 ratio had been reported for the observation at Hateruma Island (HAT, 24.06°N, 123.81°E), located at approximately 100 km east of YON. Nevertheless, the absolute values for YON were 34 % larger than those for HAT. Additionally, the monthly average in February 2020 for YON showed no marked change, whereas that for HAT showed an abrupt considerable decrease associated with the FFCO2 emission decrease in China presumably caused by the COVID-19 lockdown. Investigating the diurnal variations, we found that the local influences were larger at YON, especially during daytime, than at HAT. Using nighttime data (20-6 LST) and a longer time window (84 h), we succeeded in reducing the local influences and the resulting monthly mean ΔCO2/ΔCH4 ratio showed considerable similarity to that observed at HAT including the abrupt decrease in February 2020. These results convinced us that the ΔCO2/ΔCH4 ratio could be successfully used to investigate the relative emission strength in the upwind region. [ABSTRACT FROM AUTHOR]

Atmospheric nitrous oxide (N2O) contributes to global warming and stratospheric ozone depletion, so reducing uncertainty in estimates of emissions from different sources is important for climate policy. In this study, we simulate atmospheric N2O using an atmospheric chemistry-transport model (ACTM), and the results are first compared with the in situ measurements. Five combinations of known (a priori) N2O emissions due to natural soil, agricultural land, other human activities, and sea-air exchange are used. The N2O lifetime is 127.6 ± 4.0 yr in the control ACTM simulation (range indicates interannual variability). Regional N2O emissions are optimized using Bayesian inverse modeling for 84 partitions of the globe at monthly intervals, using measurements at 42 sites around the world covering 1997 - 2019. The best estimated global land and ocean emissions are 12.99 ± 0.22 TgN yr-1 and 2.74 ± 0.27 TgN yr-1, respectively, for 2000 - 2009, and 14.30 ± 0.20 TgN yr-1 and 2.91 ± 0.27 TgN yr-1, respectively, for 2010 - 2019. On regional scales, we find that the most recent ocean emission estimation, with lower emissions in the Southern Ocean regions, fits better with that predicted by the inversions. Marginally higher (lower) emissions than the inventory/model for the tropical (extratropical) land regions are estimated and validated using independent aircraft observations. Global land and ocean emission variabilities show a statistically significant correlation with El Niño Southern Oscillation (ENSO). Analysis of regional land emissions shows increases over America (Temperate North, Central, and Tropical), Central Africa, and Asia (South, East, and Southeast) between the 2000s and 2010s. Only Europe as a whole recorded a slight decrease in N2O emissions due to the chemical industry. Our inversions suggest revisions to seasonal emission variations for three of the 15 land regions (East Asia, Temperate North America, and Central Africa), and the Southern Ocean region. The terrestrial ecosystem model (Vegetation Integrative SImulator for Trace Gases) can simulate annual total emissions in agreement with the observed N2O growth rate since 1978, but the lag-time scales of N2O emissions from nitrogen fertilizer application may need to be revised. [ABSTRACT FROM AUTHOR]