Rapid hydrolysis of NO2 at High Ionic Strengths of Deliquesced Aerosol Particles.

Nitrogen dioxide (NO2) hydrolysis in deliquesced aerosol particles forms nitrous acid and nitrate and thus impacts air quality, climate, and the nitrogen cycle. Traditionally, it is considered to proceed far too slowly in the atmosphere. However, the significance of this process is highly uncertain because kinetic studies have only been made in dilute aqueous solutions but not under high ionic strength conditions of the aerosol particles. Here, we use laboratory experiments, air quality models, and field measurements to examine the effect of the ionic strength on the reaction kinetics of NO2 hydrolysis. We find that high ionic strengths (I) enhance the reaction rate constants (kI) by more than an order of magnitude compared to that at infinite dilution (kI=0), yielding log10(kI/kI=0) = 0.04I or rate enhancement factor = 100.04I. A state-of-the-art air quality model shows that the enhanced NO2 hydrolysis reduces the negative bias in the simulated concentrations of nitrous acid by 28% on average when compared to field observations over the North China Plain. Rapid NO2 hydrolysis also enhances the levels of nitrous acid in other polluted regions such as North India and further promotes atmospheric oxidation capacity. This study highlights the need to evaluate various reaction kinetics of atmospheric aerosols with high ionic strengths.

Long-term variations in surface ozone at the Longfengshan Regional Atmosphere Background Station in Northeast China and related influencing factors.

Surface ozone (O3) is a crucial air pollutant that affects air quality, human health, agricultural production, and climate change. Studies on long-term O3 variations and their influencing factors are essential for understanding O3 pollution and its impact. Here, we conducted an analysis of long-term variations in O3 during 2006-2022 at the Longfengshan Regional Atmosphere Background Station (LFS; 44.44°N, 127.36°E, 330.5 m a.s.l.) situated on the northeastern edge of the Northeast China Plains. The maximum daily 8-h average (MDA8) O3 fluctuated substantially, with the annual MDA8 decreasing significantly during 2006-2015 (-0.62 ppb yr-1, p < 0.05), jumping during 2015-2016 and increasing clearly during 2020-2022. Step multiple linear regression models for MDA8 were obtained using meteorological variables, to decompose anthropogenic and meteorological contributions to O3 variations. Anthropogenic activities acted as the primary drivers of the long-term trends of MDA8 O3, contributing 73% of annual MDA8 O3 variability, whereas meteorology played less important roles (27%). Elevated O3 at LFS were primarily associated with airflows originating from the North China Plain, Northeast China Plain, and coastal areas of North China, primarily occurring during the warm months (May-October). Based on satellite products of NO2 and HCHO columns, the O3 photochemical regimes over LFS revealed NOx-limited throughout the period. NO2 increased first, reaching peak in 2011, followed by substantial decrease; while HCHO exhibited significant increase, contributing to decreasing trend in MDA8 O3 during 2006-2015. The plateauing NO2 and decreasing HCHO may contribute to the increase in MDA8 O3 in 2016. Subsequently, both NO2 and HCHO exhibited notable fluctuations, leading to significant changes in O3. The study results fill the gap in the understanding of long-term O3 trends in high-latitude areas in the Northeast China Plain and offer valuable insights for assessing the impact of O3 on crop yields, forest productivity, and climate change.

A review of indoor nitrous acid (HONO) pollution: Measurement techniques, pollution characteristics, sources, and sinks.

Indoor air quality is of major concern for human health and well-being. Nitrous acid (HONO) is an emerging indoor pollutant, and its indoor mixing ratios are usually higher than outdoor levels, ranging from a few to tens of parts per billion (ppb). HONO exhibits adverse effects to human health due to its respiratory toxicity and mutagenicity. Additionally, HONO can easily undergo photodissociation by ultraviolet light to produce hydroxyl radicals (OH•), which in turn trigger a series of further photochemical oxidation reactions of primary or secondary pollutants. The accumulation of indoor HONO can be attributed to both direct emissions from combustion sources, such as cooking, and secondary formation resulting from enhanced heterogeneous reactions of NOx on indoor surfaces. During the day, the primary sink of indoor HONO is photolysis to OH• and NO. Moreover, adsorption and/or reaction on indoor surfaces, and diffusion to the outside atmosphere contribute to HONO loss both during the day and at night. The level of indoor HONO is also affected by human occupancy, which can influence household factors such as temperature, humidity, light irradiation, and indoor surfaces. This comprehensive review article summarized the research progress on indoor HONO pollution based on indoor air measurements, laboratory studies, and model simulations. The environmental and health effects were highlighted, measurement techniques were summarized, pollution levels, sources and sinks, and household influencing factors were discussed, and the prospects in the future were proposed.

Severe photochemical pollution formation associated with strong HONO emissions from dew and guttation evaporation.

The unknown daytime source of HONO has been extensively investigated due to unexplained atmospheric oxidation capacity and current modelling bias, especially during cold seasons. In this study, abrupt morning increases in atmospheric HONO at a rural site in the North China Plain (NCP) were observed almost on daily basis, which were closely linked to simultaneous rises in atmospheric water vapor content and NH3 concentrations. Dew and guttation water formation was frequently observed on wheat leaves, from which water samples were taken and chemically analyzed for the first time. Results confirmed that such natural processes likely governed the daily nighttime deposition and daytime release of HONO and NH3, which have not been considered in the numerous HONO budget studies investigating its large missing daytime source in the NCP. The dissolved HONO and NH3 in leaf surface water droplets reached 1.4 and 23 mg L-1 during the morning on average, resulting in averaged atmospheric HONO and NH3 increases of 0.89 ± 0.61 and 43.7 ± 29.3 ppb during morning hours, with relative increases of 186 ± 212 % and 233 ± 252 %, respectively. The high atmospheric oxidation capacity contained within HONO was stored in near surface liquid water (such as dew, guttation and soil surface water) during nighttime, which prevented its atmospheric dispersion after sunset and protected it from photodissociation during early morning hours. HONO was released in a blast during later hours with stronger solar radiation, which triggered and then accelerated daytime photochemistry through the rapid photolysis of HONO and subsequent OH production, especially under high RH conditions, forming severe secondary gaseous and particulate pollution. Results of this study demonstrate that global ecosystems might play significant roles in atmospheric photochemistry through nighttime dew formation and guttation processes.

Influence of meteorological factors on open biomass burning at a background site in Northeast China.

Biomass burning (BB) is a very important emission source that significantly adversely impacts regional air quality. BB produces a large number of primary organic aerosol (POA) and black carbon (BC). Besides, BB also provides many precursors for secondary organic aerosol (SOA) generation. In this work, the ratio of levoglucosan (LG) to organic carbon (OC) and the fire hotspots map was used to identify the open biomass burning (OBB) events, which occurred in two representative episodes, October 13 to November 30, 2020, and April 1 to April 30, 2021. The ratio of organic aerosol (OA) to reconstructed PM2.5 concentration (PM2.5*) increased with the increase of LG/OC. When LG/OC ratio is higher than 0.03, the highest OA/PM2.5* ratio can reach 80%, which means the contribution of OBB to OA is crucial. According to the ratio of LG to K+, LG to mannosan (MN) and the regional characteristics of Longfengshan, it can be determined that the crop residuals are the main fuel. The occurrence of OBB coincides with farmers' preferred choices, i.e., burning biomass in "bright weather". The "bright weather" refers to the meteorological conditions with high temperature, low humidity, and without rain. Meteorological factors indirectly affect regional biomass combustion pollution by influencing farmers' active choices.

Exploring HONO formation and its role in driving secondary pollutants formation during winter in the North China Plain.

Daytime HONO photolysis is an important source of atmospheric hydroxyl radicals (OH). Knowledge of HONO formation chemistry under typical haze conditions, however, is still limited. In the Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain in 2018, we investigated the wintertime HONO formation and its atmospheric implications at a rural site Gucheng. Three different episodes based on atmospheric aerosol loading levels were classified: clean periods (CPs), moderately polluted periods (MPPs) and severely polluted periods (SPPs). Correlation analysis revealed that HONO formation via heterogeneous conversion of NO2 was more efficient on aerosol surfaces than on ground, highlighting the important role of aerosols in promoting HONO formation. Daytime HONO budget analysis indicated a large missing source (with an average production rate of 0.66 ± 0.26, 0.97 ± 0.47 and 1.45 ± 0.55 ppbV/hr for CPs, MPPs and SPPs, respectively), which strongly correlated with photo-enhanced reactions (NO2 heterogeneous reaction and particulate nitrate photolysis). Average OH formation derived from HONO photolysis reached up to (0.92 ± 0.71), (1.75 ± 1.26) and (1.82 ± 1.47) ppbV/hr in CPs, MPPs and SPPs respectively, much higher than that from O3 photolysis (i.e., (0.004 ± 0.004), (0.006 ± 0.007) and (0.0035 ± 0.0034) ppbV/hr). Such high OH production rates could markedly regulate the atmospheric oxidation capacity and hence promote the formation of secondary aerosols and pollutants.

Identifying the O3 chemical regime inferred from the weekly pattern of atmospheric O3, CO, NOx, and PM10: Five-year observations at a center urban site in Shanghai, China.

Ozone pollution is still considered a severe environmental problem in China despite the fact that great efforts have been devoted to monitoring and alleviating its impact by the Chinese government including the establishment of numerous observational networks. One of the issues most relevant to the design of emission reduction policies is to distinguish the O3 chemical regime. Here a method of quantifying the fraction of the radical loss versus NOx chemistry was applied to identify the O3 chemical regime inferred from the weekly pattern of atmospheric O3, CO, NOx, and PM10, which were monitored by Ministry of Ecology and Environment of China (MEEC). During spring and autumn, O3 and the total odd oxygen (Ox, Ox = O3 + NO2) weekend afternoon concentrations are both higher than the weekday values during 2015-2019 except in 2016, while CO and NOx weekend morning concentrations were generally both smaller than weekday values except 2017. Results from the calculated values of fraction of the radical loss by NOx chemistry relative to total radical loss (Ln/Q) suggested a volatile organic compound (VOC)-limited regime at this site in the spring of 2015-2019, as expected from the decreasing trend in NOx concentration and essentially constant CO after 2017. With respect to autumn, a shift from a transition regime during 2015-2017 to a VOC-limited regime in 2018 was found, which rapidly took place to a NOx-limited regime in 2019. No significant differences were detected in the Ln/Q values under different assumptions on photolysis frequencies both in spring and autumn mostly from 2015 to 2019, giving the same conclusion of determining the O3 sensitivity regime. This study develops a new method in determining the O3 sensitivity regime in the typical season in China and provides insight into efficient O3 control strategies in different seasons.

Validating HONO as an Intermediate Tracer of the External Cycling of Reactive Nitrogen in the Background Atmosphere.

In the urban atmosphere, nitrogen oxide (NOx═NO + NO2)-related reactions dominate the formation of nitrous acid (HONO). Here, we validated an external cycling route of HONO and NOx, i.e., formation of HONO resulting from precursors other than NOx, in the background atmosphere. A chemical budget closure experiment of HONO and NOx was conducted at a background site on the Tibetan Plateau and provided direct evidence of the external cycling. An external daytime HONO source of 100 pptv h-1 was determined. Both soil emissions and photolysis of nitrate on ambient surfaces constituted likely candidate mechanisms characterizing this external source. The external source dominated the chemical production of NOx with HONO as an intermediate tracer. The OH production was doubled as a result of the external cycling. A high HONO/NOx ratio (0.31 ± 0.06) during the daytime was deduced as a sufficient condition for the external cycling. Literature review suggested the prevalence of high HONO/NOx ratios in various background environments, e.g., polar regions, pristine mountains, and forests. Our analysis validates the prevalence of external cycling in general background atmosphere and highlights the promotional role of external cycling regarding the atmospheric oxidative capacity.

First long-term surface ozone variations at an agricultural site in the North China Plain: Evolution under changing meteorology and emissions.

Significant upward trends in surface ozone (O3) have been widely reported in China during recent years, especially during warm seasons in the North China Plain (NCP), exerting adverse environmental effects on human health and agriculture. Quantifying long-term O3 variations and their attributions helps to understand the causes of regional O3 pollution and to formulate according control strategy. In this study, we present long-term trends of O3 in the warm seasons (April-September) during 2006-2019 at an agricultural site in the NCP and investigate the relative contributions of meteorological and anthropogenic factors. Overall, the maximum daily 8-h average (MDA8) O3 exhibited a weak decreasing trend with large interannual variability. < 6 % of the observed trend could be explained by changes in meteorological conditions, while the remaining 94 % was attributed to anthropogenic impacts. However, the interannual variability of warm season MDA8 O3 was driven by both meteorology (36 ± 28 %) and anthropogenic factors (64 ± 27 %). Daily maximum temperature was the most essential factor affecting O3 variations, followed by ultraviolet radiation b (UVB) and boundary layer height (BLH), with rising temperature trends inducing O3 inclines throughout April to August, while UVB mainly influenced O3 during summer months. Under changes in emissions and air quality, warm season O3 production regime gradually shifted from dominantly VOCs-limited during 2006-2015 to NOx-limited afterwards. Relatively steady HCHO and remarkably rising NOx levels resulted in the fast decreasing MDA8 O3 (-2.87 ppb yr-1) during 2006-2012. Rapidly decreasing NOx, flat or slightly increasing HCHO promoted O3 increases during 2012-2015 (9.76 ppb yr-1). While afterwards, slow increases in HCHO and downwards fluctuating NOx led to decreases in MDA8 O3 (-4.97 ppb yr-1). Additionally, continuous warming trends might promote natural emissions of O3 precursors and magnify their impacts on agricultural O3 by inducing high variability, which would require even more anthropogenic reduction to compensate for.

[Characteristics and Impact Factors of Number Concentration of Primary Biological Aerosol Particles in Beijing].

Primary biological aerosol particles (PBAP) are an important part of ambient aerosols. Both living and dead organisms not only influence human health and air quality but also play important roles in regulating certain atmospheric processes and affect the hydrological cycle and climate change. In this study, flow cytometry (FCM) was utilized in combination with the simultaneous use of permeant (SYBR Green I) and impermeant (propidium iodide, PI) nucleic acid fluorescent staining to detect and quantify the viable and dead airborne biological particles. At the same time, based on this method, the dead/viable PBAP in a Beijing urban area was detected and quantified. Moreover, the influence of environmental factors on the concentrations of primary biological aerosol particles was illuminated. The results showed that the media number concentration of dead and alive PBAP in the Beijing urban area during summer (1.03×106 m-3 and 7.43×105 m-3, respectively) were higher than those during winter (7.34×105 m-3and 6.18×105 m-3, respectively). Statistical analysis showed that there was no significant correlation between PBAP number concentration and environmental factors, i.e., meteorological conditions and air quality, showing a weak positive correlation with temperature and humidity and weak negative correlations with O3, maximum wind speed, and sunshine duration. The number concentration of PBAP was weakly correlated with the mass concentration of PM2.5 but positively correlated with that of coarse particulate matter (PM2.5-10). Both stable weather and dust transport could increase the number concentration of PBAP in Beijing.

Joint increase of aerosol scattering efficiency and aerosol hygroscopicity aggravate visibility impairment in the North China Plain.

China's "Blue Sky Action Plan" aimed at tremendous improvements in atmospheric visibility. While stringent emission control policies have substantially brought down PM2.5 mass concentrations, visibility improved much less than expected due to non-linear responses of visibility changes to PM2.5 reductions. In this study, we used long-term continuous humidified nephelometer system measurements of multi-wavelength aerosol scattering coefficients in both dry state and controlled relative humidity conditions in the North China Plain during spring and summer to attempt disentanlge the non-linear relationsips between visibility and PM2.5 mass.Aerosol scattering efficiency, optical hygroscopicity and air relative humidity are key factors for relating PM2.5 mass to visibility. It was found that aerosol volume scattering efficiencies (VSEs) were highly correlated (r > 0.8) with aerosol scattering coefficients. The continuous decrease of aerosol scattering Ångström exponent during pollution episodes revealed dominant contributions of secondary aerosol formation to aerosol size growth and mass accumulation, explaining aerosol VSE increases. Moreover, the optical hygroscopicity parameter κsca that describes the aerosol light scattering enhancement abilities through water uptake increased jointly with VSE and aggravated the visibility degradation during middle to final stages of pollution episodes. Thus, low visibility events (<3 km) only occurred when VSE and κsca were at their highest levels. The contribution of aerosol water to visibility degradation increased as visibility decreased, and contributed dominantly to visibility degradation under extremely low visibility conditions (<1 km). However, under hazy visibility conditions (3-10 km), which occurred most frequently, both aerosol water and scattering efficiency enhancement played significant roles. For setting up more efficient emission control strategies targeting on visibility improvement, our results highly encourage more future research on the linkages between secondary aerosol formation mechanisms and co-variations of aerosol scattering efficiency and aerosol hygroscopicity on the NCP.

Volatile organic compounds in wintertime North China Plain: Insights from measurements of proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS).

The characteristics of wintertime volatile organic compounds (VOCs) in the North China Plain (NCP) region are complicated and remain obscure. VOC measurements were conducted by a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) at a rural site in the NCP from November to December 2018. Uncalibrated ions measured by PTR-ToF-MS were quantified and the overall VOC compositions were investigated by combining the measurements of PTR-ToF-MS and gas chromatography-mass spectrometer/flame ionization detector (GC-MS/FID). The measurement showed that although atmospheric VOCs concentrations are often dominated by primary emissions, the secondary formation of oxygenated VOCs (OVOCs) is non-negligible in the wintertime, i.e., OVOCs accounts for 42% ± 7% in the total VOCs (151.3 ± 75.6 ppbV). We demonstrated that PTR-MS measurements for isoprene are substantially overestimated due to the interferences of cycloalkanes. The chemical changes of organic carbon in a pollution accumulation period were investigated, which suggests an essential role of fragmentation reactions for large, chemically reduced compounds during the heavy-polluted stage in wintertime pollution. The changes of emission ratios of VOCs between winter 2011 and winter 2018 in the NCP support the positive effect of "coal to gas" strategies in curbing air pollutants. The high abundances of some key species (e.g. oxygenated aromatics) indicate the strong emissions of coal combustion in wintertime of NCP. The ratio of naphthalene to C8 aromatics was proposed as a potential indicator of the influence of coal combustion on VOCs.

The importance of hydroxymethanesulfonate (HMS) in winter haze episodes in North China Plain.

Hydroxymethanesulfonate (HMS), a key marker species of aqueous-phase processing, plays a significant role in sulfur budget in atmosphere. Here we have a comprehensive characterization of HMS at urban and rural sites in North China Plain (NCP) by using the real-time measurements from a high-resolution aerosol mass spectrometer (AMS) and a single-particle AMS together with offline filter analysis. Our results showed much higher winter concentration of HMS at the rural site (average±1σ: 2.58 ± 2.56 µg m-3) than that (1.70 ± 2.68 µg m-3) in Beijing due to the more frequent fog events, low particle acidity and high concentration of precursors. The HMS on average contributed 6.3% and 5.2% to organic aerosol (OA), and 16% and 12% to the total particulate sulfur, at the rural and urban sites, respectively. HMS was highly correlated with aqueous-phase secondary OA and sulfate, and its contribution to the total particulate sulfur increased significantly as a function of relative humidity demonstrating the effective HMS production from aqueous-phase processing. Single-particle analysis showed that HMS-containing particles were mainly mixed with amine-related compounds. In addition, we found that organosulfur compounds (OS) estimated from sulfur-containing fragments of AMS correlated well with HMS at both urban and rural sites. While OS at the rural site was dominated by HMS, other types of OS were also important in urban area. The high HMS also affected the estimation of particle acidity using the AMS measured and predicted ammonium, particularly during severe haze episodes. Overall, our results demonstrated the importance of HMS in winter in NCP, and it could be more important in total particulate sulfur budget as the continuous decrease in sulfate in the future.

On the fossil and non-fossil fuel sources of carbonaceous aerosol with radiocarbon and AMS-PMF methods during winter hazy days in a rural area of North China plain.

Regional transport is a key source of carbonaceous aerosol in many Chinese megacities including Beijing. The sources of carbonaceous aerosol in urban areas have been studied extensively but are poorly known in upwind rural areas. This work aims to quantify the contributions of fossil and non-fossil fuel emissions to carbonaceous aerosols at a rural site in North China Plain in winter 2016. We integrated online high resolution-time of flight-aerosol mass spectrometer (HR-TOF-AMS) observations and radiocarbon (14C) measurements of fine particles with Positive Matrix Factorization (PMF) analysis as well as Extended Gelencsér (EG) method. We found that fine particle concentration is much higher at the rural site than in Beijing during the campaign (Dec 7, 2016 to Jan 8, 2017). PMF analysis of the AMS data showed that coal-combustion related organic aerosol (CCOA + Oxidized CCOA) and more oxidized oxygenated organic aerosol (MO-OOA) contributed 48% and 30% of organic matter to non-refractory PM1 (NR-PM1) mass. About 2/3 of the OC and EC were from fossil-fuel combustion. The EG method, combining AMS-PMF and 14C data, showed that primary and secondary OC from fossil fuel contribute 35% and 22% to total carbon (TC), coal combustion emission dominates the fossil fuel sources, and biomass burning accounted for 21% of carbonaceous aerosol. In summary, our results confirm that fossil fuel combustion was the dominant source of carbonaceous aerosol during heavy pollution events in the rural areas. Significant emissions of solid fuel carbonaceous aerosols at rural areas can affect air quality in downwind cities such as Beijing and Tianjin, highlighting the benefits of energy transition from solid fuels to cleaner energy in rural areas.

Observational insights into the compound environmental effect for 2-methyltetrols formation under humid ambient conditions.

Laboratory experiments suggest acid-catalyzed aqueous-phase production can promote the formation of isoprene SOA, i.e., 2-methyltetrols. In this study we use ambient observations of the 2-methyltetrols along with other chemical measurements, as well as meteorological factors to investigate the relative importance of environmental influence for isoprene epoxydiols (IEPOX) SOA formation under atmospheric humidity conditions. The 2-Methyltetrols revealed good relationships with temperature and total solar radiation, but were weakly correlated with aerosol acidity and SO42-. EC-scaled 2-methyltetrols were observed to vary in a narrow pH range (1.5-2.0), indicating aerosol acidity was not a limiting factor for 2-methyltetrols formation. High values of 2-methyltetrols were consistently observed at high total solar radiation, the strong dependence of total solar radiation demonstrated that photochemical processes dominated 2-methyltetrols formation in humid environments. Although 2-methyltetrols can be enhanced by acid-catalyzed aqueous-phase reactions, it is not sufficient to compensate the synchronously weakened photochemical activity influence, leading to an obvious net decrease in the formation of 2-methyltetrols in the ambient. Moreover, aerosol droplet acidity was reduced under high liquid water content (LWC) condition, subsequently diminishing the enhancement of SOA formation by acidity. Overall, our results highlight that the environmental impact factors are highly variable and interplay, influencing the production of 2-methyltetrols, and suggest that the formation pathway of 2-methyltetrols is insensitive to aerosol acidity but dominated by photochemical production process in humid environments.

CircRNA expression profiles and circRNA-miRNA-mRNA crosstalk in allergic rhinitis.

BACKGROUND: Circular RNAs (circRNAs) are involved in inflammation; however, their role in allergic rhinitis (AR) remains unclear. In this study, we analyzed circRNA expression and identified a circRNA-miRNA-mRNA network through which circRNAs regulate AR pathogenesis. METHODS: We analyzed circRNA, miRNA, and mRNA expression profiles in the nasal mucosa by high-throughput sequencing (HTS), using a fold-change >1.5 and p-value < 0.05 to pinpoint significantly differentially expressed (DE) circRNAs, miRNAs, and mRNAs in AR. A DEcircRNA-DEmiRNA-DEmRNA crosstalk network was then constructed using bioinformatics and statistical analysis. Gene ontology and Kyoto encyclopedia of genes and genomes pathway analyses were performed to identify the biological terms enriched in the network; whereas RT-PCR and Sanger sequencing were used to confirm the circRNAs. RESULTS: A total of 264 DEcircRNAs were identified by HTS, including 120 upregulated and 144 downregulated in AR compared to controls. A DEcircRNA-DEmiRNA-DEmRNA crosstalk network was constructed with 17 miRNAs, 11 circRNAs, 29 mRNAs, and 64 interaction pairs. These genes were involved in the Wnt signaling pathway, TNF biosynthesis, inflammatory responses, the PI3K-Akt signaling pathway, and Toll-like receptors. Of the 11 DEcircRNAs, hsa_circ_0008668 and circTRIQK were upregulated, whereas hsa_circ_0029853 and circRNA_01002 were downregulated in AR tissues. Sanger sequencing confirmed the back-splicing junctions of these circRNAs. CONCLUSIONS: We constructed a novel DEcircRNA-DEmiRNA-DEmRNA network for AR that provides a basis for future studies to investigate its underlying molecular mechanisms.

Light absorption of black carbon and brown carbon in winter in North China Plain: comparisons between urban and rural sites.

The light absorption black carbon (BC) and brown carbon (BrC) are two important sources of uncertainties in radiative forcing estimate. Here we investigated the light absorption enhancement (Eabs) of BC due to coated materials at an urban (Beijing) and a rural site (Gucheng) in North China Plain (NCP) in winter 2019 by using a photoacoustic extinctiometer coupled with a thermodenuder. Our results showed that the average (±1σ) Eabs was 1.32 (±0.15) at the rural site, which was slightly higher than that at the urban site (1.24 ± 0.15). The dependence of Eabs on coating materials was found to be relatively limited at both sites. However, Eabs presented considerable increases as a function of relative humidity below 70%. Further analysis showed that Eabs during non-heating period in Beijing was mainly caused by secondary components, while it was dominantly contributed by enhanced primary emissions in heating season at both sites. In particular, aerosol particles mixed with coal combustion emissions had a large impact on Eabs (>1.40), while the fresh traffic emissions and freshly oxidized secondary OA (SOA) had limited Eabs (1.00-1.23). Although highly aged or aqueous-phase processed SOA coated on BC showed the largest Eabs, their contributions to the bulk absorption enhancement were generally small. We also quantified the absorption of BrC and source contributions. The results showed the BrC absorption at the rural site was nearly twice that of urban site, yet absorption Ångström exponents were similar. Multiple linear regression analysis highlighted the major sources of BrC being coal combustion emissions and photochemical SOA at both sites with additional biomass burning at the rural site. Overall, our results demonstrated the relatively limited winter light absorption enhancement of BC in different chemical environments in NCP, which needs be considered in regional climate models to improve BC radiative forcing estimates.

Aerosol Promotes Peroxyacetyl Nitrate Formation During Winter in the North China Plain.

Peroxyacetyl nitrate (PAN) is an important indicator for photochemical pollution, formed similar to ozone in the photochemistry of certain volatile organic compounds (VOCs) in the presence of nitrogen oxides, and has displayed surprisingly high concentrations during wintertime that were better correlated to particulate rather than ozone concentrations, for which the reasons remained unknown. In this study, wintertime observations of PAN, VOCs, PM2.5, HONO, and various trace gases were investigated to find the relationship between aerosols and wintertime PAN formation. Wintertime photochemical pollution was affirmed by the high PAN concentrations (average: 1.2 ± 1.1 ppb, maximum: 7.1 ppb), despite low ozone concentrations. PAN concentrations were determined by its oxygenated VOC (OVOC) precursor concentrations and the NO/NO2 ratios and can be well parameterized based on the understanding of their chemical relationship. Data analysis and box modeling results suggest that PAN formation was mostly contributed by VOC aging processes involving OH oxidation or photolysis rather than ozonolysis pathways. Heterogeneous reactions on aerosols have supplied key photochemical oxidants such as HONO, which produced OH radicals upon photolysis, promoting OVOC formation and thereby enhancing PAN production, explaining the observed PM2.5-OVOC-PAN intercorrelation. In turn, parts of these OVOCs might participate in the formation of secondary organic aerosol, further aggravating haze pollution as a feedback. Low wintertime temperatures enable the long-range transport of PAN to downwind regions, and how that will impact their oxidation capacity and photochemical pollution requires further assessment in future studies.

Simultaneous observation of atmospheric peroxyacetyl nitrate and ozone in the megacity of Shanghai, China: Regional transport and thermal decomposition.

Atmospheric peroxyacetyl nitrate (PAN) and ozone (O3) are two typical indicators for photochemical pollution that have adverse effects on the ecosystem and human health. Observation networks for these pollutants have been expanding in developed regions of China, such as North China Plain (NCP) and Pearl River Delta (PRD), but are sparse in Yangtze River Delta (YRD), meaning their concentration and influencing factors remain poorly understood. Here, we performed a one-year measurement of atmospheric PAN, O3, particulate matter with aerodynamic diameter smaller than 2.5 µm (PM2.5), nitrogen oxides (NOx), carbon monoxide (CO), and meteorological parameters from December 2016 to November 2017 in Shanghai. Overall, high hourly maximum PAN and O3 were found to be 7.0 and 185 ppbv in summer, 6.2 and 146 ppbv in autumn, 5.8 and 137 ppbv in spring, and 6.0 and 76.7 ppbv in winter, respectively. Continental air masses probably carried atmospheric pollutants to the sampling site, while frequent maritime winds brought in less polluted air masses. Furthermore, positive correlations (R: 0.72-0.85) between PAN and O3 were found in summer, indicating a predominant role of photochemistry in their formation. Unlike in summer, weak or no correlations between PAN and O3 were featured during the other seasons, especially in winter, due to their different loss pathways. Unexpectedly, positive correlations between PAN and PM2.5 were found in all seasons. During summer, moderate correlation could be attributed to the strong photochemistry acting as a common driver in the formation of secondary aerosols and PAN. During winter, high PM2.5 might promote PAN production through HONO production, hence resulting in a good positive correlation. Additionally, the loss of PAN by thermal decomposition (TPAN) only accounted for a small fraction (ca. 1%) of the total (PAN + TPAN) during a typical winter episode, while it significantly reached 14.4 ppbv (71.1% of the total) in summer.

Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN): integrated analysis and intensive winter campaign 2018.

Fine-particle pollution associated with winter haze threatens the health of more than 400 million people in the North China Plain. The Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN) investigated the physicochemical mechanisms leading to haze formation with a focus on the contributions of multiphase processes in aerosols and fogs. We integrated observations on multiple platforms with regional and box model simulations to identify and characterize the key oxidation processes producing sulfate, nitrate and secondary organic aerosols. An outdoor twin-chamber system was deployed to conduct kinetic experiments under real atmospheric conditions in comparison to literature kinetic data from laboratory studies. The experiments were spanning multiple years since 2017 and an intensive field campaign was performed in the winter of 2018. The location of the site minimizes fast transition between clean and polluted air masses, and regimes representative for the North China Plain were observed at the measurement location in Gucheng near Beijing. The consecutive multi-year experiments document recent trends of PM2.5 pollution and corresponding changes of aerosol physical and chemical properties, enabling in-depth investigations of established and newly proposed chemical mechanisms of haze formation. This study is mainly focusing on the data obtained from the winter campaign 2018. To investigate multiphase chemistry, the results are presented and discussed by means of three characteristic cases: low humidity, high humidity and fog. We find a strong relative humidity dependence of aerosol chemical compositions, suggesting an important role of multiphase chemistry. Compared with the low humidity period, both PM1 and PM2.5 show higher mass fraction of secondary inorganic aerosols (SIA, mainly as nitrate, sulfate and ammonium) and secondary organic aerosols (SOA) during high humidity and fog episodes. The changes in aerosol composition further influence aerosol physical properties, e.g., with higher aerosol hygroscopicity parameter κ and single scattering albedo SSA under high humidity and fog cases. The campaign-averaged aerosol pH is 5.1 ± 0.9, of which the variation is mainly driven by the aerosol water content (AWC) concentrations. Overall, the McFAN experiment provides new evidence of the key role of multiphase reactions in regulating aerosol chemical composition and physical properties in polluted regions.