Unveiling the Molecular Characteristics, Origins, and Formation Mechanism of Reduced Nitrogen Organic Compounds in the Urban Atmosphere of Shanghai Using a Versatile Aerosol Concentration Enrichment System.

Reduced nitrogen-containing organic compounds (NOCs) in aerosols play a crucial role in altering their light-absorption properties, thereby impacting regional haze and climate. Due to the low concentration levels of individual NOCs in the air, the utilization of accurate detection and quantification technologies becomes essential. For the first time, this study investigated the diurnal variation, chemical characteristics, and potential formation pathways of NOCs in urban ambient aerosols in Shanghai using a versatile aerosol concentration enrichment system (VACES) coupled with HPLC-Q-TOF-MS. The results showed that NOCs accounted over 60% of identified components of urban organic aerosols, with O/N < 3 compounds being the major contributors (>70%). The predominance of the positive ionization mode suggested the prevalence of reduced NOCs. Higher relative intensities and number fractions of NOCs were observed during nighttime, while CHO compounds showed an opposite trend. Notably, a positive correlation between the intensity of NOCs and ammonium during the nighttime was observed, suggesting that the reaction of ammonium to form imines may be a potential pathway for the formation of reduced NOCs during the nighttime. Seven prevalent types of reduced NOCs in autumn and winter were identified and characterized by an enrichment of CH2 long-chain homologues. These NOCs included alkyl, cyclic, and aromatic amides in CHON compounds, as well as heterocyclic or cyclic amines and aniline homologue series in CHN compounds, which were associated with anthropogenic activities and may be capable of forming light-absorbing chromophores or posing harm to human health. The findings highlight the significant contributions of both primary emissions and ammonium chemistry, particularly amination processes, to the pollution of reduced NOCs in Shanghai's atmosphere.

Quantification and Characterization of Fine Plastic Particles as Considerable Components in Atmospheric Fine Particles.

The negative effects of air pollution, especially fine particulate matter (PM2.5, particles with an aerodynamic diameter of ≤2.5 µm), on human health, climate, and ecosystems are causing significant concern. Nevertheless, little is known about the contributions of emerging pollutants such as plastic particles to PM2.5 due to the lack of continuous measurements and characterization methods for atmospheric plastic particles. Here, we investigated the levels of fine plastic particles (FPPs) in PM2.5 collected in urban Shanghai at a 2 h resolution by using a novel versatile aerosol concentration enrichment system that concentrates ambient aerosols up to 10-fold. The FPPs were analyzed offline using the combination of spectroscopic and microscopic techniques that distinguished FPPs from other carbon-containing particles. The average FPP concentrations of 5.6 µg/m3 were observed, and the ratio of FPPs to PM2.5 was 13.2% in this study. The FPP sources were closely related to anthropogenic activities, which pose a potential threat to ecosystems and human health. Given the dramatic increase in plastic production over the past 70 years, this study calls for better quantification and control of FPP pollution in the atmosphere.

PM1.0-Nitrite Heterogeneous Formation Demonstrated via a Modified Versatile Aerosol Concentration Enrichment System Coupled with Ion Chromatography.

Particulate nitrite is a critical source of hydroxyl radicals; however, it lacks high-resolution methods due to its low abundance and stability to explore its formation mechanism. In this study, a modified versatile aerosol concentration enrichment system (VACES) coupled with ion chromatography (IC) was used to measure particulate NO2- hourly online and achieve a lowered detection limit of 10-3 µg m-3. VACES-IC was used to observe a high- and low-concentration events of PM1.0-NO2- in Shanghai, corresponding to the ambient-level concentrations of 0.34 and 0.05 µg m-3, respectively. The morning peak concentrations of NO2- even exceeded 3σ (standard deviation) in the high-concentration event due to the reduction of NO2 by aerosol SO32- based on kinetics and regression analysis. This implies that controlling SO2 emissions would be an effective strategy to decrease morning NO2- concentrations, correspondingly reducing the kinetic formation of SO42- by 20.8-34.8%. However, after sunrise, NO2- formation was primarily attributed to NO2 hydrolysis at pH 4.97-6.14. In the low-concentration event, NO2 hydrolysis also accounted for an overwhelming proportion (∼90%) of NO2- formation. This work estimates the contribution of different paths to particulate NO2- formation based on newly established high-resolution measurements.

Hydrogen sulfide functions as a micro-modulator bound at the copper active site of Cu/Zn-SOD to regulate the catalytic activity of the enzyme.

The present study examines whether there is a mechanism beyond the current concept of post-translational modifications to regulate the function of a protein. A small gas molecule, hydrogen sulfide (H2S), was found to bind at active-site copper of Cu/Zn-SOD using a series of methods including radiolabeled binding assay, X-ray absorption near-edge structure (XANES), and crystallography. Such an H2S binding enhanced the electrostatic forces to guide the negatively charged substrate superoxide radicals to the catalytic copper ion, changed the geometry and energy of the frontier molecular orbitals of the active site, and subsequently facilitated the transfer of an electron from the superoxide radical to the catalytic copper ion and the breakage of the copper-His61 bridge. The physiological relevance of such an H2S effect was also examined in both in vitro and in vivo models where the cardioprotective effects of H2S were dependent on Cu/Zn-SOD.

Accurate observation of black and brown carbon in atmospheric fine particles via a versatile aerosol concentration enrichment system (VACES).

Carbonaceous aerosols (CAs) are major components of fine particulate matter (PM2.5) that dramatically influence the energy budget of Earth. However, accurate assessment of the climatic impacts of CAs is still challenging due to the large uncertainties remaining in the measurement of their optical properties. In this respect, a modified versatile aerosol concentration enrichment system integrated into optical instruments (VACES-OPTS) was set up to increase particle concentration and amplify signal-noise ratio during optical measurement. Based on the novel technique, this study was able to lower the detection limit of CAs by an order of magnitude under high temporal resolution (2 h) and small sampling flow (6 L min-1). Besides, stable and reliable optical data were obtained for absorption apportionment and source identification of black carbon (BC) and brown carbon (BrC). In the field application of the new system, high absorption coefficient of CAs in Shanghai, China was witnessed. Further analysis of the contribution of black carbon BC and BrC to light absorption revealed that BrC could account for over 15% of the total absorption at 370 nm. According to the potential source contribution function model (PSCF) classification, CAs with strong light absorption in urban Shanghai originated not only from highly polluted inland China but also from active marine ship emissions.

Significant trade-off for the impact of Grain-for-Green Programme on ecosystem services in North-western Yunnan, China.

Ecological restoration can mitigate human disturbance to the natural environment and restore ecosystem functions. China's Grain-for-Green Programme (GFGP) has been widely adopted in the last 15years and exerted significant impact on land-use and ecosystem services. North-western Yunnan is one of the key areas of GFGP implementation in the upper Yangtze River. Promotion of ecosystem services in this region is of great importance to the ecological sustainability of Yangtze River watershed. In this study, remote sensing and modelling techniques are applied to analyse the impact of GFGP on ecosystem services. Results show that the transformation from non-irrigated farmland to forestland could potentially improve soil conservation by 24.89%. Soil conservation of restored forest was 78.17% of retained forest while net primary production (NPP) already reached 88.65%, which suggested different recovery rates of NPP and soil conservation. Increasing extent of GFGP implementation improved soil conservation but decreased NPP and water yield at sub-watershed scale, which revealed trade-offs between ecosystem services under ecological restoration. Future ecosystem management and GFGP policy-making should consider trade-offs of ecosystem services in order to achieve sustainable provision of ecosystem services.