Search

In this study, ship-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements were performed in the East China Sea (ECS) area in June 2017. The tropospheric slant column densities (SCDs) of nitrogen dioxide (NO2), sulfur dioxide (SO2), and formaldehyde (HCHO) were retrieved from the measured spectra using the differential optical absorption spectroscopy (DOAS) technique. Using the simple geometric approach, the SCDs of different trace gases observed at a 15° elevation angle were adopted to convert into tropospheric vertical column densities (VCDs). During this campaign, the averaged VCDs of NO2, SO2, and HCHO in the marine environment over the ECS area are 6.50 x 1015, 4.28 x 1015, and 7.39 x 1015 molec cm-2 [ABSTRACT FROM AUTHOR]

The Environmental trace gas Monitoring Instrument (EMI) onboard the Chinese high-resolution remote sensing satellite GaoFen-5 is an ultraviolet–visible imaging spectrometer, aiming to quantify the global distribution of tropospheric and stratospheric trace gases and planned to be launched in spring 2018. The preflight calibration phase is essential to characterize the properties and performance of the EMI in order to provide information for data processing and trace gas retrievals. In this paper, we present the first EMI measurement of nitrogen dioxide (NO2) from a gas absorption cell using scattered sunlight as the light source by the differential optical absorption spectroscopy technique. The retrieved NO2 column densities in the UV and Vis wavelength ranges are consistent with the column density in the gas cell calculated from the NO2 mixing ratio and the length of the gas cell. Furthermore, the differences of the retrieved NO2 column densities among the adjoining spatial rows of the detector are less than 3%. This variation is similar to the well-known “stripes-pattern” of the Ozone Monitoring Instrument and is probably caused by remaining systematic effects like a nonperfect description of the individual instrument functions. Finally, the signal-to-noise ratios of EMI in-orbit measurements of NO2 are estimated on the basis of on-ground scattered sunlight measurements and radiative transfer model simulations. Based on our results, we conclude that the EMI is capable of measuring the global distribution of the NO2 column with the retrieval precision and accuracy better than 3% for the tested wavelength ranges and viewing angles. [ABSTRACT FROM AUTHOR]

Restrictions on human activities remarkably reduced emissions of air pollutants in China during the COVID-19 lockdown periods. However, distinct responses of O3 concentrations were observed across China. In the Beijing–Tianjin–Hebei (BTH) and Yangtze River Delta (YRD) regions, O3 concentrations were enhanced by 90.21 and 71.79% from pre-lockdown to lockdown periods in 2020, significantly greater than the equivalent concentrations for the same periods over 2015–2019 (69.99 and 43.62%, p < 0.001). In contrast, a decline was detected (−1.1%) in the Pearl River Delta (PRD) region. To better understand the underlying causes for these inconsistent responses across China, we adopted the least absolute shrinkage and selection operator (Lasso) and ordinary linear squares (OLS) methods in this study. Statistical analysis indicated that a sharp decline in nitrogen dioxide (NO2) was the major driver of enhanced O3 in the BTH region as it is a NOx-saturated region. In the YRD region, season-shift induced changes in the temperature/shortwave radiative flux, while lockdown induced declines in NO2, attributable to the rise in O3. In the PRD region, the slight drop in O3 is attributed to the decreased intensity of radiation. The distinct regimes of the O3 response to the COVID-19 lockdown in China offer important insights into different O3 control strategies across China. [ABSTRACT FROM AUTHOR]

Nitrogen dioxide (NO 2) in the lower marine atmosphere, mainly emitted by maritime shipping, plays a crucial role in air pollution formation and global human health. However, few measurements of marine atmospheric NO 2 hinder knowledge of trace gas trends and atmospheric chemistry evolution due to shipping emissions. In this study, we use long-term satellite observations of tropospheric NO 2 column from the European TROPOspheric Monitoring Instrument (TROPOMI) and the Chinese Environmental trace gases Monitoring Instrument (EMI) to analyze marine atmospheric NO 2 variations, especially during the global COVID-19 pandemic and escalating geopolitical crises. First, we demonstrate the detection of NO 2 enhancements along shipping routes, including the North Atlantic route, the North Pacific route, and the Cape route, indicating significant emissions of atmospheric NO 2 from on-ocean shipping. Second, we observe and quantify the response of marine atmospheric NO 2 concentrations to major shipping events, such as the Suez Canal blockage, the Los Angeles-Long Beach port congestion, and the Russia-Ukraine war, resulting in local NO 2 concentration variations of approximately 40% decrease to 70% increase. Long-term analysis reveals reduced NO 2 concentrations in most coastal ports and maritime shipping routes during the COVID-19 lockdown, with reductions exceeding 50% or durations lasting up to 200 days. However, some rapidly developing ports, such as Beibu Gulf (China) and Dakar (Senegal), did not experience a decrease in NO 2 concentrations, suggesting that local authorities need to pay more attention to these fast-growing yet underestimated emission sources. In addition, by excluding the impact of meteorology using statistical models, we find that the current Emission Control Area (ECA) policies have effectively reduced NO 2 concentrations in Chinese coastal ports. These results contribute to understanding spatiotemporal characteristics of marine atmospheric NO 2 , including ports and open-sea shipping routes, and guide further ECA policies to control marine NO 2 pollution. • New-generation satellites including TROPOMI and EMI can detect enhanced NO 2 pollution over maritime shipping routes. • Major shipping events have led to from −40% to 70% variations in local marine atmospheric NO 2 concentrations. • The COVID-19 pandemic reduced NO 2 pollution by > 50%, for a maximum of 200 days in the world's top ports. • Shipping emission control policies have effectively improved NO 2 pollution in Chinese ports since January 2019. [ABSTRACT FROM AUTHOR]