By Sankar Ray
Japanese scientists in a study found a marked fall in Carbon Dioxide in China due to outbreak of Covid 19 right from February-March 2020, according to a paper published in Nature on 29 October 2020- ‘Detection of fossil-fuel CO2 plummet in China due to Covid 19 by observation at Hateruma’, authored by Yasmori Tohijima, Prabir K Patra, Yosuke Niwa, Hitoshi Mukai, Motoki Sasakawa and Toshinobi Machida, of whom Patra is an Indian atmospheric physicist.
The study is undertaken by Japan’s National Institute for Environmental Studies (NIES)/Center for Global Environment Research (CGER) which has been conducting global monitoring of atmospheric greenhouse gases by using a variety of platforms, including ground sites, commercial cargo ships, aircraft, and satellites. It has an observation station at Hateruma Island (HAT)for comprehensive atmospheric measurements. Located in a marginal region of continental East Asia, the outflow of the continental air masses with elevated greenhouse gas concentrations is often captured at HAT.
A global observation network for atmospheric greenhouse gases has been developed in Japan since the 1960s.It evaluates the global anthropogenic and natural flux budgets quantitatively estimates the regional/country-scale emission changes. In sync with all this the study has been undertaken to detect the COVID-19 influence on atmospheric CO2 and, if possible, quantitatively evaluate the emission change in China – crucially important to test the capacity of our observation networks. National restrictions owing to the COVID-19 situation give us a unique opportunity to validate some of the hypotheses that are needed to successfully implement the Paris Agreement.
The research admitted that the outbreak of the new coronavirus, Covid 19, was first identified in Wuhan, China, in December 2019, as a sequel to which, the Chinese government of China adopted a range of measures including a lockdown of Wuhan, shut-down of the inter-city transportation, and reduction of socioeconomic activity at the end of January 2020 to prevent the spread of COVID-19 within China and to the outside world. For these steps, “ it was estimated that the emissions of fossil-fuel-derived CO2 (FFCO2) in China decreased by about 25 per cent during January–February. Significant reductions in nitrogen dioxide (NO2), which is an atmospheric pollutant mainly produced by fossil fuel combustion in engines, were also detected over China by remote sensing satellites.
The abstract of the paper reads, “The COVID-19 pandemic caused drastic reductions in carbon dioxide (CO2) emissions, but due to its large atmospheric reservoir and long lifetime, no detectable signal has been observed in the atmospheric CO2 growth rate. Using the variabilities in CO2 (ΔCO2) and methane (ΔCH4) observed at Hateruma Island, Japan during 1997–2020, they found a traceable CO2 emission reduction in China during February–March 2020.
The monitoring station at Hateruma Island observes the outflow of Chinese emissions during winter and spring. A systematic increase in the ΔCO2/ΔCH4 ratio, governed by synoptic wind variability, well corroborated the increase in China’s fossil-fuel CO2 (FFCO2) emissions during 1997–2019. However, the ΔCO2/ΔCH4 ratios showed significant decreases of 29 ± 11 and 16 ± 11 mol mol−1 in February and March 2020, respectively, relative to the 2011–2019 average of 131 ± 11 mol mol−1. By projecting these observed ΔCO2/ΔCH4 ratios on transport model simulations, we estimated reductions of 32 ± 12% and 19 ± 15% in the FFCO2 emissions in China for February and March 2020, respectively, compared to the expected emissions. Our data are consistent with the abrupt decrease in the economic activity in February, a slight recovery in March, and return to normal in April, which was calculated based on the COVID-19 lockdowns and mobility restriction datasets.”
In contrast to earlier studies that revealed ‘synoptic-scale variations’ (defined as hourly to weekly variations in the CO2 and CH4 time series, and their variabilities are termed as ΔCO2 and ΔCH4, respectively) during the winter season, constraining emissions from continental East Asia, this study examines whether the reduced economic activity in China ‘has caused any detectable change in the CO2 synoptic variations at HAT. The study was based on the assumption that the CO2 and CH4 flux signals had similar spatial distributions in the outflow region of China during the winter through spring, and thus produced coinciding peaks and troughs in atmospheric variability observed at HA
But the study found no evidence of detection of ‘China’s emission reduction in atmospheric CO2 concentrations. It is also unclear whether atmospheric observations can support the direct estimation of reductions in FFCO2 emissions in near-real-time.’ Moreover, t is quite difficult to relate such anomalies to the change in FFCO2 emissions.
The atmospheric CO2 signal due to changes in FFCO2 ‘weakens by atmospheric transport as the distance between the source and observation site (or receptor) -., HAT- , increases. Yet the rather simple air mass trajectories and the suppressed terrestrial biospheric exchange in the winter months allow us to evaluate the FFCO2 sources in China from the synoptic-scale variabilities at HAT’ The researchers also discussed the ratios of ΔCO2 and ΔCH4 for removing the first-order effect of atmospheric transport on the CO2 synoptic variability. (IPA Service)