[Analysis on the Characteristics of Oxidation Potential and Influence Sources of PM2.5 in Baoding City in Winter].

In order to explore the characteristics of PM2.5 oxidation potential and its impact sources in the suburbs of Baoding City in the winter of 2018, the dithiothreitol (DTT) method was used to determine the reactive oxygen species in PM2.5. Pearson correlation was used to analyze the relationship between the chemical components in PM2.5 and the oxidation potential. PMF was used to analyze the pollution source of DTTv. Firstly, the results showed that the average value of ρ(PM2.5) in Baoding in winter was (140.96±70.67) µg·m-3 higher than the concentration of PM2.5 in Beijing during the same period. Secondly, both the DTTv and DTTm values of the oxidation potential were higher during the day than those at night[DTTv was (2.37±0.76) nmol·(min·m3)-1 during the day and (2.14±1.17) nmol·(min·m3)-1 at night; DTTm was (0.96±0.60) pmol·(min·µg)-1 during the day and (0.76±0.41) pmol·(min·µg)-1 at night]. This showed that the atmospheric environment during the day was more conducive to the generation and survival of active oxygen. In addition, through the analysis of the correlation between DTTv and carbohydrates, inorganic salt ions, OC, EC, and water-soluble metals, it was found that metal Fe, oxalate, and NH4+ had a high correlation with DTTv both day and night (during the day:r=0.790, P<0.01, at night:r=0.960, P<0.01; during the day:r=0.609, P<0.01, at night:r=0.577, P<0.01; during the day:r=0.627, P<0.01, at night:r=0.586, P<0.01), and OC, levoglucan, mannan, and galactan were only highly correlated with DTTv in the daytime (r=0.675, P<0.01; r=0.701, P<0.01; r=0.662, P<0.01; r=0.671, P<0.01). Finally, according to the PMF source analysis, there were five main pollution sources that affected DTTv:secondary sources (29.9%), biomass combustion (29.2%), dust (11.2%), mineral dust and industrial sources (8.6%), and traffic sources (21.1%). The influence of secondary sources and biomass combustion on DTTv was dominant.

Decrease of atmospheric black carbon and CO2 concentrations due to COVID-19 lockdown at the Mt. Waliguan WMO/GAW baseline station in China.

The Coronavirus Disease 2019 (COVID-19) lockdown policy reduced anthropogenic emissions and impacted the atmospheric chemical characteristics in Chinese urban cities. However, rare studies were conducted at the high mountain site. In this work, in-situ measurements of light absorption by carbonaceous aerosols and carbon dioxide (CO2) concentrations were conducted at Waliguan (WLG) over the northeastern Tibetan Plateau of China from January 3 to March 30, 2020. The data was employed to explore the influence of the COVID-19 lockdown on atmospheric chemistry in the background-free troposphere. During the sampling period, the light absorption near-infrared (>470 nm) was mainly contributed by BC (>72%), however, BC and brown carbon (BrC) contributed equally to light absorption in the short wavelength (∼350 nm). The average BC concentrations in the pre-, during and post-lockdown were 0.28 ±â€¯0.25, 0.18 ±â€¯0.16, and 0.28 ±â€¯0.20 µg m-3, respectively, which decreased by approximately 35% during the lockdown period. Meanwhile, CO2 also showed slight decreases during the lockdown period. The declined BC was profoundly attributed to the reduced emissions (∼86%), especially for the combustion of fossil fuels. Moreover, the declined light absorption of BC, primary and secondary BrC decreased the solar energy absorbance by 35, 15, and 14%, respectively. The concentration weighted trajectories (CWT) analysis suggested that the decreased BC and CO2 at WLG were exclusively associated with the emission reduction in the eastern region of WLG. Our results highlighted that the reduced anthropogenic emissions attributed to the lockdown in the urban cities did impact the atmospheric chemistry in the free troposphere of the Tibetan Plateau.