Aerosol liquid water in PM2.5 and its roles in secondary aerosol formation at a regional site of Yangtze River Delta.

Aerosol liquid water content (ALWC) plays an important role in secondary aerosol formation. In this study, a whole year field campaign was conducted at Shanxi in north Zhejiang Province during 2021. ALWC estimated by ISORROPIA-II was then investigated to explore its characteristics and relationship with secondary aerosols. ALWC exhibited a highest value in spring (66.38 µg/m3), followed by winter (45.08 µg/m3), summer (41.64 µg/m3), and autumn (35.01 µg/m3), respectively. It was supposed that the secondary inorganic aerosols (SIA) were facilitated under higher ALWC conditions (RH > 80%), while the secondary organic species tended to form under lower ALWC levels. Higher RH (> 80%) promoted the NO3- formation via gas-particle partitioning, while SO42- was generated at a relative lower RH (> 50%). The ALWC was more sensitive to NO3- (R = 0.94) than SO42- (R = 0.90). Thus, the self-amplifying processes between the ALWC and SIA enhanced the particle mass growth. The sensitivity of ALWC and OX (NO2 + O3) to secondary organic carbon (SOC) varied in different seasons at Shanxi, more sensitive to aqueous-phase reactions (daytime R = 0.84; nighttime R = 0.54) than photochemical oxidation (daytime R = 0.23; nighttime R = 0.41) in wintertime with a high level of OX (daytime: 130-140 µg/m3; nighttime: 100-140 µg/m3). The self-amplifying process of ALWC and SIA and the aqueous-phase formation of SOC will enhance aerosol formation, contributing to air pollution and reduction of visibility.

Critical Role of Simultaneous Reduction of Atmospheric Odd Oxygen for Winter Haze Mitigation.

The lockdown due to COVID-19 created a rare opportunity to examine the nonlinear responses of secondary aerosols, which are formed through atmospheric oxidation of gaseous precursors, to intensive precursor emission reductions. Based on unique observational data sets from six supersites in eastern China during 2019-2021, we found that the lockdown caused considerable decreases (32-61%) in different secondary aerosol components in the study region because of similar-degree precursor reductions. However, due to insufficient combustion-related volatile organic compound (VOC) reduction, odd oxygen (Ox = O3 + NO2) concentration, an indicator of the extent of photochemical processing, showed little change and did not promote more decreases in secondary aerosols. We also found that the Chinese provinces and international cities that experienced reduced Ox during the lockdown usually gained a greater simultaneous PM2.5 decrease than other provinces and cities with an increased Ox. Therefore, we argue that strict VOC control in winter, which has been largely ignored so far, is critical in future policies to mitigate winter haze more efficiently by reducing Ox simultaneously.

Widespread 2013-2020 decreases and reduction challenges of organic aerosol in China.

High concentrations of organic aerosol (OA) occur in Asian countries, leading to great health burdens. Clean air actions have resulted in significant emission reductions of air pollutants in China. However, long-term nation-wide trends in OA and their causes remain unknown. Here, we present both observational and model evidence demonstrating widespread decreases with a greater reduction in primary OA than in secondary OA (SOA) in China during the period of 2013 to 2020. Most of the decline is attributed to reduced residential fuel burning while the interannual variability in SOA may have been driven by meteorological variations. We find contrasting effects of reducing NOx and SO2 on SOA production which may have led to slight overall increases in SOA. Our findings highlight the importance of clean energy replacements in multiple sectors on achieving air-quality targets because of high OA precursor emissions and fluctuating chemical and meteorological conditions.

Endoplasmic reticulum stress participates in apoptosis of HeLa cells exposed to TPHP and OH-TPHP via the eIF2α-ATF4/ATF3-CHOP-DR5/P53 signaling pathway.

Purpose: Triphenyl phosphate (TPHP) is a widely used organophosphate flame retardant, which can be transformed in vivo into diphenyl phosphate (DPHP) and 4-hydroxyphenyl phosphate (diphenyl) ester (OH-TPHP) through biotransformation process. Accumulation of TPHP and its derivatives in biological tissues makes it necessary to investigate their toxicity and molecular mechanism. Methods: The present study evaluated the cellular effects of TPHP, DPHP, and OH-TPHP on cell survival, cell membrane damage, oxidative damage, and cell apoptosis using HeLa cells as in vitro model. RNA sequencing and bioinformatics analysis were conducted to monitor the differently expressed genes, and then RT-qPCR and Western bolt were used to identify potential molecular mechanisms and key hub genes. Results: Results showed that OH-TPHP had the most significant cytotoxic effect in HeLa cells, followed by TPHP; and no significant cytotoxic effects were observed for DPHP exposure within the experimental concentrations. Biological function enrichment analysis suggested that TPHP and OH-TPHP exposure may induce endoplasmic reticulum stress (ERS) and cell apoptosis. The nodes filtering revealed that ERS and apoptosis related genes were involved in biological effects induced by TPHP and OH-TPHP, which may be mediated through the eukaryotic translation initiation factor 2α/activating transcription factor 4 (ATF4)/ATF3- CCAAT/ enhancer-binding protein homologous protein (CHOP) cascade pathway and death receptor 5 (DR5) /P53 signaling axis. Conclusion: Above all, these findings indicated that ERS-mediated apoptosis might be one of potential mechanisms for cytotoxicity of TPHP and OH-TPHP.

Characteristics and sources of ambient Volatile Organic Compounds (VOCs) at a regional background site, YRD region, China: Significant influence of solvent evaporation during hot months.

Continuous measurement of 98 volatile organic compounds (VOCs) was conducted during 2017-2019 at a regional background site (Shanxi) located at northeast of Zhejiang Province, YRD region, China. The average concentration of total VOCs (TVOCs) was 25.4 ± 18.4 ppbv, and an increasing trend (+12.2 %) was observed. Alkanes were the most abundant VOC group among all seasons, accounting for 43.5 % of TVOCs. Oxygenated VOCs (OVOCs), aromatics, halides and alkenes contributed 15.9 %, 15.7 %, 11.7 % and 10.3 % of TVOCs concentration, respectively. Biogenic VOCs (BVOCs) and OVOCs showed distinguished diurnal cycle from primary anthropogenic VOCs. Photochemical reactivity analysis based on ozone formation potential (OFP) and OH loss rate (LOH) indicated that aromatics and alkenes were the most significant contributor, respectively. Toluene, xylene (m/p- and o-), ethene and propene were the largest contributor of annual OFP, with the mean OFP being 33.8 ± 44.3 µg·m-3, 31.9 ± 32.1 µg·m-3, 9.29 ± 11.4 µg·m-3, 22.1 ± 21.3 µg·m-3 and 12.8 ± 19.5 µg·m-3, respectively. Seven sources were identified with positive matrix factorization (PMF): petrochemical industry (13.8 %), biogenic emission (1.0 %), solvent usage-toluene (16.9 %), vehicular exhaust (43.8 %), Integrated circuits industry (3.8 %), solvent usage-C8 aromatics (10.9 %), and gasoline evaporation (9.8 %). Vehicular exhaust was the most significant source (43.8 %) during the whole measurement period. Solvent usage, petrochemical industry, and gasoline evaporation showed high temperature dependency. The integrated contribution of solvent usage and industrial processes were higher than vehicular exhaust during hot months. These sources also have higher chemical reactivities and can contribute more on O3 formation. Our results are helpful on determining the control strategies aiming at alleviating O3 pollution.

Interactive enhancements of ascorbic acid and iron in hydroxyl radical generation in quinone redox cycling.

Quinones are toxicological substances in inhalable particulate matter (PM). The mechanisms by which quinones cause hazardous effects can be complex. Quinones are highly active redox molecules that can go through a redox cycle with their semiquinone radicals, leading to formation of reactive oxygen species. Electron spin resonance spectra have been reported for semiquinone radicals in PM, indicating the importance of ascorbic acid and iron in quinone redox cycling. However, these findings are insufficient for understanding the toxicity associated with quinone exposure. Herein, we investigated the interactions among anthraquinone (AQ), ascorbic acid, and iron in hydroxyl radical (·OH) generation through the AQ redox cycling process in a physiological buffer. We measured ·OH concentration and analyzed the free radical process. Our results showed that AQ, ascorbic acid, and iron have synergistic effects on ·OH generation in quinone redox cycling; i.e., ascorbyl radical oxidized AQ to semiquinone radical and started the redox cycling, iron accelerated this oxidation and enhanced ·OH generation through Fenton reactions, while ascorbic acid and AQ could help iron to release from quartz surface and enhance its bioavailability. Our findings provide direct evidence for the redox cycling hypothesis about airborne particle surface quinone in lung fluid.

Long-term trend of haze pollution and impact of particulate matter in the Yangtze River Delta, China.

Haze pollution caused by heavy particulate matter (PM) loading brings significant damage in eastern China. Long-term monitoring from 1980 to 2011 and 1-year field measurement in 2011-2012 are used for investigating visibility variation and the impact of PM pollution for the Yangtze River Delta (YRD). It was found that visual range in the YRD endured a sharp reduction from 13.2 km to 10.5 km during 1980-2000. Average mass extinction efficiency (MEE) for inhalable PM (PM10) is 2.25 m(2)/g in 2001-2011, and extinction coefficient due to PM10 is 207 Mm(-1), accounting for 36.2% of total extinction coefficient. MEE of PM2.5 and PM2.5-10 are 4.08 m(2)/g and 0.58 m(2)/g, respectively. Extinction coefficient due to PM2.5 and PM2.5-10 is 198 Mm(-1) (39.6%) and 20 Mm(-1) (4.0%) in 2011-2012. Maximum daily concentration of PM10 and PM2.5 is estimated to be 63 µg/m(3) (RH: 73%) and 38 µg/m(3) (RH: 70%) to keep visual range above 10 km. Fine particulate matter is the key factor for haze pollution improvement in the YRD area.