High levels of ultrafine particles (UFPs; diameter of less than 50 nm) are frequently produced from new particle formation under urban conditions, with profound implications on human health, weather, ...and climate. However, the fundamental mechanisms of new particle formation remain elusive, and few experimental studies have realistically replicated the relevant atmospheric conditions. Previous experimental studies simulated oxidation of one compound or a mixture of a few compounds, and extrapolation of the laboratory results to chemically complex air was uncertain. Here, we show striking formation of UFPs in urban air from combining ambient and chamber measurements. By capturing the ambient conditions (i.e., temperature, relative humidity, sunlight, and the types and abundances of chemical species), we elucidate the roles of existing particles, photochemistry, and synergy of multipollutants in new particle formation. Aerosol nucleation in urban air is limited by existing particles but negligibly by nitrogen oxides. Photooxidation of vehicular exhaust yields abundant precursors, and organics, rather than sulfuric acid or base species, dominate formation of UFPs under urban conditions. Recognition of this source of UFPs is essential to assessing their impacts and developing mitigation policies. Our results imply that reduction of primary particles or removal of existing particles without simultaneously limiting organics from automobile emissions is ineffective and can even exacerbate this problem.
Organosulfates (OSs) with ambiguous formation mechanisms are a potential source of missing secondary organic aerosol (SOA) in current atmospheric models. In this study, we chemically characterized ...OSs and nitrooxy-OSs (NOSs) formed under the influence of biogenic emissions and anthropogenic pollutants (e.g., NOx, SO42−) in summer in Beijing. An ultrahigh-resolution mass spectrometer equipped with an electrospray ionization source was applied to examine the overall molecular composition of S-containing organics. The number and intensities of S-containing organics, the majority of which could be assigned as OSs and NOSs, increased significantly during pollution episodes, which indicated their importance for SOA accumulation. To further investigate the distribution and formation of OSs and NOSs, high-performance liquid chromatography coupled with mass spectrometry was employed to quantify 10 OSs and 3 NOS species. The total concentrations of quantified OSs and NOSs were 41.4 and 13.8 ng m−3, respectively. Glycolic acid sulfate was the most abundant species among all the quantified species, followed by monoterpene NOSs (C10H16NO7S−). The total concentration of three isoprene OSs was 14.8 ng m−3 and the isoprene OSs formed via the HO2 channel were higher than those formed via the NO ∕ NO2 channel. The OS concentration coincided with the increase in acidic sulfate aerosols, aerosol acidity, and liquid water content (LWC), indicating the acid-catalyzed aqueous-phase formation of OSs in the presence of acidic sulfate aerosols. When sulfate dominated the accumulation of secondary inorganic aerosols (SIAs; sulfate, nitrate, and ammonium; SO42− ∕ SIA > 0.5), OS formation would obviously be promoted as the increasing of acidic sulfate aerosols, aerosol LWC, and acidity (pH < 2.8). Otherwise, acid-catalyzed OS formation would be limited by lower aerosol acidity when nitrate dominated the SIA accumulation. The nighttime enhancement of monoterpene NOSs suggested their formation via the nighttime NO3-initiated oxidation of monoterpene under high-NOx conditions. However, isoprene NOSs are presumed to form via acid-catalyzed chemistry or reactive uptake of oxidation products of isoprene. This study provides direct observational evidence and highlights the secondary formation of OSs and NOSs via the interaction between biogenic precursors and anthropogenic pollutants (NOx, SO2, and SO42−). The results imply that future reduction in anthropogenic emissions can help to reduce the biogenic SOA burden in Beijing or other areas impacted by both biogenic emissions and anthropogenic pollutants.
In this paper, we investigated the mechanisms, kinetics, and toxicity evaluation of the OH-initiated reaction of coniferyl alcohol (4-(3-hydroxy-1-propenyl)-2-methoxyphenol) in the atmosphere using ...theoretical calculations. The initial reaction of coniferyl alcohol with OH radicals had two pathways, H-abstraction and OH-addition reactions. The total reaction rate constants were 2.32 × 10−9 cm3 molecule−1 s−1 (in gas-phase) and 9.44 × 109 s−1 M−1 (in liquid-phase) for the preliminary reactions of coniferyl alcohol with OH radicals at 298 K, respectively, and the half-lives of the total reaction (including all initial H-abstraction and OH-addition reactions) of coniferyl alcohol with OH radical in the atmosphere, urban and remote clouds were 8.3 × 10−2 h, 5.83 × 103 h and 9.27 × 102 h, respectively. The temperature had a strong and positive influence on the initial reaction rate constant. The branching ratios of H-abstraction and OH-addition reactions were 3.68% and 97.69%, respectively, making the OH-addition reactions become dominant reactions. The ecotoxicity evaluation revealed that the toxicity levels of coniferyl alcohol and its products were similar and non-toxic. However, all these products have developmental toxicity, with most of them having no mutagenicity. Therefore, further attention should be paid to the oxidation process and product toxicity evaluation of coniferyl alcohol in the atmosphere.
To improve air quality, the Beijing government has employed several air
pollution control measures since the 2008 Olympics. In order to investigate
organic aerosol sources after the implementation of ...these measures, ambient
fine particulate matter was collected at a regional site in Changping (CP) and
an urban site at the Peking University Atmosphere Environment Monitoring Station (PKUERS)
during the “Photochemical Smog in China” field campaign in summer
2016. Chemical mass balance (CMB) modeling and the tracer yield method
were used to apportion primary and secondary organic sources. Our results
showed that the particle concentration decreased significantly during the
last few years. The apportioned primary and secondary sources explained
62.8 ± 18.3 and 80.9 ± 27.2 % of the measured OC at CP and
PKUERS, respectively. Vehicular emissions served as the dominant source.
Except for gasoline engine emissions, the contributions of all the other primary
sources decreased. In addition, the anthropogenic SOC, i.e., toluene SOC, also
decreased, implying that deducting primary emissions can reduce anthropogenic
SOA. In contrast to the SOA from other regions in the world where biogenic
SOA was dominant, anthropogenic SOA was the major contributor to SOA,
implying that deducting anthropogenic VOC emissions is an efficient way to
reduce SOA in Beijing. Back-trajectory cluster analysis results showed that
high mass concentrations of OC were observed when the air mass was from
the south. However, the contributions of different primary organic sources were
similar, suggesting regional particle pollution. The ozone concentration
and temperature correlated well with the SOA concentration. Different
correlations between day and night samples suggested different SOA
formation pathways. Significant enhancement of SOA with increasing particle
water content and acidity was observed in our study, suggesting that aqueous-phase acid-catalyzed reactions may be the important SOA formation mechanism
in summer in Beijing.
12-Molybdophosphoric acid supported on titania (HPMo/TiO2) was prepared by one-step in situ method and first used to catalyze the transesterification of dimethyl carbonate and phenol to diphenyl ...carbonate, which exhibited excellent catalytic activity. The highly dispersed HPMo and stable Keggin structure played a significant role for the excellent catalytic performance of HPMo/TiO2. With the conditions of weight ratio of HPMo to TiO2 of 1:1, calcined temperature of 300°C, catalyst amount of 0.6g and reaction time 10h, the phenol conversion and transesterification selectivity reached 50.4% and 99.4%, respectively. Moreover, after four consecutive runs, the phenol conversion slowly decreased from 44.7% to 29.5%, and the transesterification selectivity maintained at 99%. The characterization of XPS and FT-IR presented that the transformation of Mo6+ to Mo5+ and the adsorption of reaction intermediate were the key factors for the decrease of catalytic activity.
•HPMo/TiO2 was first prepared by one-step in situ method.•HPMo/TiO2 revealed superior catalytic activity to other heterogeneous catalysts reported.•Highly dispersed HPMo and Keggin structure played significant role for the excellent catalytic performance.•The transformation of Mo6+ to Mo5+ decreased the catalytic activity.
Fly ash originating from municipal solid waste incineration (MSWI) is potentially hazardous waste and is harmful to the surrounding area once it enters the environment. In this study, we measured the ...physiochemical properties of fly ash derived from domestic waste incineration as well as the leaching toxicity of heavy metals in fly ash was contained. The results suggested that the porosity of fly ash is relatively high, and the leaching concentration of heavy metals can be greatly reduced through densification strategies in which fly ash is stabilized by chemical agents. The adsorption–desorption curve of fly ash had an obvious hysteresis loop that belongs to the H2-type hysteresis loop. Fly ash was typically mesoporous, and the silicate in fly ash was relatively stable. Its glass phase contents were higher—this allowed it to be used in ceramic tile decoration. In addition, Pb and Cd were the major heavy metals in fly ash. These heavy metals were mainly distributed in the residue. Heavy metals were easily leached out under strong acid or alkaline conditions.
In the present work, volatile organic compounds (VOCs) from vehicle exhaust and cooking fumes were investigated via simulation experiments, which covered engine emissions produced during gasoline ...direct injection (GDI) using two kinds of fuels and cooking emissions produced by preparing three domestic dishes. The distinct characteristics of VOCs emitted during the two processes were identified. Alkanes (73% mass fraction on average) and aromatics (15% on average) dominated the vehicle VOCs, while oxygenated VOCs (49%) and alkanes (29%) dominated the cooking VOCs. Isopentane (22%) was the most abundant species among the vehicle VOCs. N-hexanal (20%) dominated the cooking VOCs. The n-hexanal-to-n-pentanal ratio (3.68 ± 0.64) was utilized to identify cooking VOCs in ambient air. The ozone formation potential produced by cooking VOCs was from 1.39 to 1.93 times higher than that produced by vehicle VOCs, which indicates the significant potential contribution of cooking VOCs to atmospheric ozone. With the equivalent photochemical age increasing from 0 h to 72 h, the secondary organic aerosol formation by vehicle VOCs was from 3% to 38% higher than that of cooking VOCs. Controlling cooking emissions can reduce SOA pollution in a short time due to its higher SOA formation rate than that of vehicle VOCs within the first 30 h. However, after 30 h of oxidation, the amount of SOAs formed by vehicle exhaust emissions exceeded the amount of SOAs produced by cooking activities, implying that reducing vehicle emissions will benefit particle pollution for a longer time. Our results highlight the importance of VOCs produced by cooking fumes, which has not been given much attention before. Further, our study suggested that more research on semi-volatile organic compounds produced by cooking emissions should be conducted in the future.
A highly virulent porcine epidemic diarrhea virus (PEDV) appeared in China and spread rapidly to neighbor countries, which have led to great economic losses to the pig industry. In the present study, ...we isolated a PEDV using Vero cells and serially propagated 100 passages. PEDV SDSX16 was characterized in vitro and in vivo. The viral titers increased to 10
TCID
/mL (100th) by serial passages. The spike (S) gene and the whole gene of the SDSX16 virus was fully sequenced to assess the genetic stability and relatedness to previously identified PEDV. Along with successive passage in vitro, there were 18 nucleotides (nt) deletion occurred in the spike (S) gene resulting in a deletion of six amino acids when the SDSX16 strain was passaged to the 64th generation, and this deletion was stable until the P100. However, the ORF1a/b, M, N, E, and ORF3 genes had only a few point mutations in amino acids and no deletions. According to growth kinetics experiments, the SDSX16 deletion strain significantly enhanced its replication in Vero cells since it was passaged to the 64th generation. The animal studies showed that PEDV SDSX16-P10 caused more severe diarrhea and vomiting, fecal shedding, and acute atrophic enteritis than SDSX16-P75, indicating that SDSX16-P10 is enteropathogenic in the natural host, and the pathogenicity of SDSX16 decreased with successive passage in vitro. However, SDSX16-P10 was found to cause lower levels of cytokine expression than SDSX16-P75 using real-time PCR and flow cytometry, such as IL1β, IL6, IFN-β, TNF-α, indicating that SDSX16-P10 might inhibit the expression of cytokines. Our data indicated that successive passage in vitro resulted in virulent attenuation in vivo of the PEDV variant strain SDSX16.
Organosulfates (OSs) are an important group of secondary organic aerosols, but the key influential factors of their formation in polluted atmospheres are not well understood. In this study, we ...monitored particulate OSs (carboxy OSs, hydroxyacetone sulfate, and isoprene- and monoterpene-derived OSs) at an urban site and a regional site in Beijing and examined their compositions and formation pathways under contrasting atmospheric conditions. The quantified OSs were most abundant in the summer at the regional site due to higher biogenic emissions and favorable formation conditions (higher aerosol acidity and humidity), followed by urban summer and winter conditions. Larger fractions of inorganic sulfate were converted to organosulfur when sulfate was less abundant. This implies that OSs would play more important roles in aerosol properties as the decline of sulfate. Monoterpene-derived nitrooxy-OSs were enhanced via NO3 oxidation in the summer under high-NOx conditions at night, while the day-night variations in the winter were not as obvious. Among isoprene-OSs, IEPOX (isoprene epoxydiols)-OS formation was clearly suppressed under high-NOx conditions, while other isoprene-OSs that are favored under high-NOx conditions showed increasing formation with NOx. The results highlight that isoprene-OS formation pathways in polluted atmospheres could be different from the IEPOX-dominated regions reported for the low-NOx environments in the literature.
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