Atmospheric Oxidation Capacity Elevated during 2020 Spring Lockdown in Chengdu, China: Lessons for Future Secondary Pollution Control.

This study presents the measurement of photochemical precursors during the lockdown period from January 23, 2020, to March 14, 2020, in Chengdu in response to the coronavirus (COVID-19) pandemic. To derive the lockdown impact on air quality, the observations are compared to the equivalent periods in the last 2 years. An observation-based model is used to investigate the atmospheric oxidation capacity change during lockdown. OH, HO2, and RO2 concentrations are simulated, which are elevated by 42, 220, and 277%, respectively, during the lockdown period, mainly due to the reduction in nitrogen oxides (NOx). However, the radical turnover rates, i.e., OH oxidation rate L(OH) and local ozone production rate P(O3), which determine the secondary intermediates formation and O3 formation, only increase by 24 and 48%, respectively. Therefore, the oxidation capacity increases slightly during lockdown, which is partly attributed to unchanged alkene concentrations. During the lockdown, alkene ozonolysis seems to be a significant radical primary source due to the elevated O3 concentrations. This unique data set during the lockdown period highlights the importance of controlling alkene emission to mitigate secondary pollution formation in Chengdu and may also be applicable in other regions of China given an expected NOx reduction due to the rapid transformation to electrified fleets in the future.

Identification and quantification of IEPOX in ambient aerosols, using electron and chemical ionization sources GC/MS as their trimethylsilyl ethers, and using H-NMR.

Isoprene is the most abundant non-methane hydrocarbon (NMHC) emitted by vegetation, and the precursor that makes the greatest contribution to secondary organic aerosols (SOA) in the troposphere. Atmospheric oxidation of isoprene produces a series of reactive intermediates, isoprene epoxydiols (IEPOX). The reactive uptake of IEPOX is the significant formation pathway of atmospheric SOA. In this work, four isomers of IEPOX were synthesized, derivatized by silylation reagents, and measured by gas chromatography/mass spectrometry (GC/MS). The electron-impact (EI) and methane chemical ionization (CI) sources mass spectra of trimethylsilyl ester (TMS) derivatives of IEPOX isomers were obtained and the fragmentation behaviors of the derivatives were examined. Moreover, the hydrogen nuclear magnetic resonance (H-NMR) spectra of IEPOX isomers were also obtained and the peak intensities in the H-NMR spectra were analyzed. Based on the standard spectra, IEPOX isomers were identified in ambient PM2.5 aerosols in the Gongga Mountain (China). The peak sequence of TMS derivatives of IEPOX isomers in GC/MS chromatogram was δ4-IEPOX, δ1-IEPOX, cis-ß-IEPOX and trans-ß-IEPOX. The isomers with the highest concentrations were δ1-IEPOX (threo- and erythro-). The mass ratios of IEPOX to 2-methyltetrols were 0.02-6.0 and the concentrations of IEPOX were 0.8-41.6 ng/m3 in the PM2.5 aerosols. The current study verified the core roles of IEPOX as active intermediates in photo oxidation of isoprene in ambient atmosphere.

Short- and long-term impacts of the COVID-19 epidemic on urban PM2.5 variations: Evidence from a megacity, Chengdu.

As the new coronavirus pandemic enters its third year, its long-term impact on the urban environment cannot be ignored, especially in megacities with more than millions of people. Here, we analyzed the changes in the concentration levels, emission sources, temporal variations and holiday effects of ambient fine particulate matter (PM2.5) and its chemical components in the pre- and post-epidemic eras based on high-resolution, long time-series datasets of PM2.5 and its chemical components in Chengdu. In the post-epidemic era, the PM2.5 concentration in Chengdu decreased by 7.4%, with the components of PM2.5 decreasing to varying degrees. The positive matrix factorization (PMF) results indicated that the emissions from soil dust and industrial production were significantly lower during the COVID-19 lockdown period and post-epidemic era than those in the pre-epidemic era. In contrast, the contribution of secondary aerosols to PM2.5 during these two periods increased by 2.7% and 6.6%, respectively. Notably, we found that PM2.5 and its components substantially decreased on workdays and holidays in the post-epidemic era due to the reduced traffic volume and outdoor activities. This provides direct evidence that changes in the habitual behavior patterns of urban residents in the post-epidemic era could exert an evident positive impact on the urban environment. However, the higher PM2.5 concentration was observed due to the increased consumption of regular (As4S4, Xionghuang in Chinese) and "sulfur incense" during the Dragon Boat Festival holiday in the post-epidemic era. Finally, we examined the potential effects of sporadic COVID-19 outbreaks on the PM2.5 concentration in Chengdu, and there was no decrease in PM2.5 during two local COVID-19 outbreak events due to the strong influence of secondary pollution processes.

The effect of biochar on the migration theory of nutrient ions.

As the acidification of arable soils increases, the utilization of nutrient ions such as N, P, and K decreases substantially. It causes environmental pollution and reduces crop yields. Through previous studies, acidified soil amendments have problems such as easy-retrograde and unclear mechanism. Therefore, in this study, biochar prepared by pyrolysis using peanut shells was used as a green amendment for acidified soil. Biochar with 0, 5 and 10 % biochar ratios were applied to the acidified soil, and the improvement and mechanism were investigated via experiments and software simulations. Analysis of the software simulation results revealed that biochar had the highest unit adsorption of K+ through physical adsorption at 820.38 mg/g. This was followed by PO43-, NO3-, and NH4+ as 270.51, 235.65 and 130.93 mg/g, respectively. These ions were controlled by both electrostatic and ion-exchange adsorption processes. During the improvement, the 10 % biochar ratio group performed the best with a 65.32 % reduction in the outlet volume, and the accumulated levels of nutrient ions in the leachate dropped by 48.40-68.28 % and increased by 437.80-913.87 % in the surface soil. Nutrient ion levels decreased gradually with the increase of soil depth, which agreed with the software simulation results. This study found that applying biochar to acidified soils can provide a solution to low nutrient utilization efficiency and unclear improvement mechanism of acidified soils, and provide a partial theoretical basis for the large-scale application of biochar. Future research on biochar for soil carbon sink and microbial expansion can be strengthened to contribute to environmental protection and multi-level utilization of energy.