Secondary Organic Compounds Research Articles

Predominance of aminated water interfaces on transition-metal nanoparticulate to enhance synergetic removal of carbonyls and inhibition of CO2 production

In the context of the air quality co-benefits of carbon neutrality, conventional strategies for the end-of-pipe control reduction of volatile organic compounds (VOCs) towards carbon dioxide (CO2) need to be revised more realistically. This study explored the synergetic removal of carbonyls with low carbon emission by amine-functionalized manganese dioxide (MnO2), obtained with a method involving freezing-thawing cycles. Molecular-level characterization revealed that an ordered array of interfacial water dimers (H5O2+, a class of water-proton clusters) on the MnO2 surface enhanced the robust bonding of metal sites with amino groups. Amine-functionalized MnO2 can be negatively charged under environmental acidity to further interfacial proton-coupled electron transfers. Cooperativity in the interfacial chemical processes facilitated the selective conversion of carbonyl carbons to bicarbonated amides (NH3+HCO3−) as a reservoir of CO2. Compared with a commercially used 2,4-dinitrophenylhydrazine (DNPH) control, the nearly complete removal of a priority carbonyl mixture containing formaldehyde, acetaldehyde, and acetone was attained synergically. The secondary organic compounds in the gas phase and CO2 off-gas were suppressed.

Investigation of the Mechanism of Oxidative Potential Increase in Atmospheric Particulate Matter during Photoaging: Important Role of Aromatic Nitrogenous Compounds.

Particulate matter (PM) undergoing various aging processes in the atmosphere changes its toxicity. However, the mechanism of toxicity evolution is not fully clarified currently. This study demonstrates that photoaging promotes an increase in the oxidative potential (OP) of atmospheric PM by about 30%, and the increased OP is mainly attributed to the production of secondary organic compounds, while water-soluble metal ions contribute only 11%. The OP of nonextractable matters (NEMs) of atmospheric PM was mostly increased after photoaging, followed by water-soluble matters (WSMs). NEM can produce quinone-like functional groups and secondary persistent free radicals during photoaging, which are most likely to produce reactive oxygen species (ROS). For WSM, the conversion of low-oxidation humic-like substances (HULIS) to high-oxidation HULIS is the main reason for the increase in OP. Quinones, nitrophenols, and N-containing heterocycles are the OP contributors produced during the conversion process. Among them, quinones are the main secondary oxidizing active compounds, while nitro-phenolic compounds and N-containing heterocyclic compounds may play a catalyst-like role, facilitating the production of oxidizing active compounds and ROS in the newly converted high-oxidation HULIS. This study clarifies the secondary OP generation mechanism and provides new insights into the uncertainty of PM toxicity during atmospheric aging.

Elaborating the Atmospheric Transformation of Combined and Free Amino Acids From the Perspective of Observational Studies

AbstractProteinaceous matter (PrM) is a substantial component of bioaerosols. Although numerous studies have examined the characteristics and sources of PrM in the atmosphere, its interactions with atmospheric oxidants remain uncertain. A 1‐year observation of PrM characteristics in PM2.5 was performed in both urban Nanchang (eastern China) and suburban Guiyang (southwestern China), respectively. Glycine was the dominant free amino acid (FAA) species in urban Nanchang. In contrast, proline dominated both total free amino acids (FAAs) and total combined amino acids (CAAs) in suburban Guiyang. We found that oxidative degradation can significantly promote the release of FAAs, especially glycine, from CAAs in Nanchang. The controlled experiment on protein oxidation by hydroxyl radical suggested that the contribution of free glycine to the total FAA fraction tended to increase during the oxidative degradation of CAAs, supporting the predominance of glycine in FAAs in Nanchang and most previous observations. The composition of FAAs was mainly influenced by primary sources in suburban Guiyang with weak atmospheric degradation of PrM. These results suggest that the degradation of aerosol PrM by atmospheric oxidants can be responsible for the difference in FAA composition between the biosphere and the atmosphere, and also imply that the oxidative degradation of aerosol PrM may be a potential source of secondary organic nitrogen compounds in aerosols. Thus, this study can improve the current understanding of the composition characteristics of PrM in the biosphere and the atmosphere, as well as the liquid phase reactions of proteinaceous compounds with atmospheric oxidants.

A comprehensive examination of temporal-seasonal variations of PM1.0 and PM2.5 in taiwan before and during the COVID-19 lockdown

COVID-19 has been a significant global concern due to its contagious nature. In May 2021, Taiwan experienced a severe outbreak, leading the government to enforce strict Pandemic Alert Level 3 restrictions in order to curtail its spread. Although previous studies in Taiwan have examined the effects of these measures on air quality, further research is required to compare different time periods and assess the health implications of reducing particulate matter during the Level 3 lockdown. Herein, we analyzed the mass concentrations, chemical compositions, seasonal variations, sources, and potential health risks of PM1.0 and PM2.5 in Central Taiwan before and during the Level 3 lockdown. As a result, coal-fired boilers (47%) and traffic emissions (53%) were identified as the predominant sources of polycyclic aromatic hydrocarbons (PAHs) in PM1.0, while in PM2.5, the dominant sources of PAHs were coal-fired boilers (28%), traffic emissions (50%), and iron and steel sinter plants (22.1%). Before the pandemic, a greater value of 20.9 ± 6.92 μg/m3 was observed for PM2.5, which decreased to 15.3 ± 2.51 μg/m3 during the pandemic due to a reduction in industrial and anthropogenic emissions. Additionally, prior to the pandemic, PM1.0 had a contribution rate of 79% to PM2.5, which changed to 89% during the pandemic. Similarly, BaPeq values in PM2.5 exhibited a comparable trend, with PM1.0 contributing 86% and 65% respectively. In both periods, the OC/EC ratios for PM1.0 and PM2.5 were above 2, due to secondary organic compounds. The incremental lifetime cancer risk (ILCR) of PAHs in PM2.5 decreased by 4.03 × 10-5 during the pandemic, with PM1.0 contributing 73% due to reduced anthropogenic activities.

Low-temperature Synthesis of Carbon Nanofibers/graphite Felt Composites Under Contactless Induction Heating

In this report induction heating was used for the catalytic chemical vapor decomposition synthesis of carbon nanofibers (CNFs) on Ni-based catalyst. The CNFs were produced with a high yield at a relatively low temperature compared to that observed for conventional heating through convection and conduction. The process also occurred in the absence of secondary toxic organic compounds, formed through side reaction in the high temperature gas-phase or through decomposition on the hot wall of reactor as encountered with traditional Joule heating mode. The improved CNFs yield under induction heating was attributed to the high reaction temperature control thanks to the high temperature regulation rate provided by the induction heating coil. The local heating of the nickel nanoparticles by the electromagnetic field could also contribute to the improvement of the CNFs yield. The results obtained indicate that inductive heating mode could be of great interest for improving the heat transfer in catalytic processes and also to reduce the problem of gradient temperature occurring inside the catalyst bed during the operating of highly exothermic or endothermic processes. It is expected that such electricity-driven heating mode could have contributed in an efficient way toward the electrification of different catalytic processes in order to reduce the associated carbon footprint.

Molecular compositions and stable carbon isotopes (δ13C) of PAHs in wintertime PM2.5 in urban Xi'an, China: Implications for source distribution and atmospheric oxidation

Atmospheric polycyclic aromatic hydrocarbons (PAHs) are potentially carcinogenic and mutagenic to human beings, and thus have attracted significant attention in recent decades. Compound-specific stable carbon isotopes (δ13C) of PAHs are indicative for source identification, but have not been extensively applied in tracing atmospheric oxidation processes. In this study, we examined the molecular compositions and δ13C values of PAHs in wintertime PM2.5 in a highly polluted urban region in Norwest China. The average concentrations of total parent-PAHs (pPAHs) and oxygenated-PAHs (OPAHs) were measured as 70 ± 29 and 36 ± 17 ng m−3, respectively. The results obtained from the incremental lifetime cancer risk (ILCR) model suggested a high potential cancer risk of PAHs in the urban region. The temperoal variations of PAHs and carbonaceous fractions implied that the contribution of secondary organic compounds was limited during the severe pollution period (PM2.5 > 115 μg m−3). Both molecular diagnostic ratios and δ13C values indicated that the major emission sources of the pPAHs were coal and/or biomass burning. The δ13C value of fluorene became heavier as the OPAHs concentration increased, while the concentrations of fluorene was negatively correlated with OPAHs, indicating the secondary formation of OPAHs from fluorene oxidation in the cold season. Our results also confirmed that δ13C values of pPAHs are indeed indicative of atmospheric oxidation processes.

Real-time measurements of non-methane volatile organic compounds in the central Indo-Gangetic basin, Lucknow, India: source characterisation and their role in O3 and secondary organic aerosol formation

Abstract. Lucknow is the capital of India's largest state, Uttar Pradesh, one of South Asia's most polluted urban cities. Tropospheric photochemistry relies on non-methane volatile organic compounds (NMVOCs), which are ozone and secondary organic aerosol precursors. Using the proton-transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) at an urban background site in Lucknow, the chemical characterisation of NMVOCs was performed in real time from December 2020 to May 2021. About ∼ 173 NMVOCs from m/z 31.018 to 197.216 were measured during the study period, including aromatics, non-aromatics, oxygenates, and nitrogen-containing compounds. The campaign daily mean concentrations of the NMVOCs were 125.5 ± 37.5 ppbv. The NMVOC daily average concentrations were about ∼ 30 % higher during the winter months (December–February) than in summer (March–May). The oxygenated volatile organic compounds and aromatics were the dominant VOC families, accounting for ∼ 57 %–80 % of the total NMVOC concentrations. Acetaldehyde, acetone, and acetic acid were the major NMVOC species, 5–15 times higher than the other species. An advanced multi-linear engine (ME-2) model was used to perform the NMVOC source apportionment using positive matrix factorisation (PMF). It resolves the five main sources contributing to these organic compounds in the atmosphere. They include traffic (23.5 %), two solid fuel combustion factors, SFC 1 (28.1 %) and SFC 2 (13.2 %), secondary volatile organic compounds (SVOCs) (18.6 %), and volatile chemical products (VCPs) (16.6 %). Aged and fresh emissions from solid fuel combustion (SFCs 1 and 2) were the dominant contributors to the total NMVOCs, and compounds related to these factors had a high secondary organic aerosol (SOA) formation potential. Interestingly, the traffic factor was the second-highest contributor to the total NMVOCs, and compounds related to this factor had a high ozone formation potential. Significant differences in the composition of the two solid fuel combustions indicate the influence of local emissions and transport of regional pollution to the city. The high temperature during summer leads to more volatilisation of oxygenated VOCs, related to the VCP factor. The study is the first attempt to highlight the sources of NMVOCs and their contribution to secondary pollutant (SOA and O3) formation in the city of Lucknow during winter and summer. The insights from the study would help various stakeholders to manage primary and secondary pollutants within the city.

Aqueous-phase formation of N-containing secondary organic compounds affected by the ionic strength

The reaction of carbonyl-to-imine/hemiaminal conversion in the atmospheric aqueous phase is a critical pathway to produce the light-absorbing N-containing secondary organic compounds (SOC). The formation mechanism of these compounds has been wildly investigated in bulk solutions with a low ionic strength. However, the ionic strength in the aqueous phase of the polluted atmosphere may be higher. It is still unclear whether and to what extent the inorganic ions can affect the SOC formation. Here we prepared the bulk solution with certain ionic strength, in which glyoxal and ammonium were mixed to mimic the aqueous-phase reaction. Molecular characterization by High-resolution Mass Spectrometry was performed to identify the N-containing products, and the light absorption of the mixtures was measured by ultraviolet-visible spectroscopy. Thirty-nine N-containing compounds were identified and divided into four categories (N-heterocyclic chromophores, high-molecular-weight compounds with N-heterocycle, aliphatic imines/hemiaminals, and the unclassified). It was observed that the longer reaction time and higher ionic strength led to the formation of more N-heterocyclic chromophores and the increasing of the light-absorbance of the mixture. The added inorganic ions were proposed to make the aqueous phase somewhat viscous so that the molecules were prone to undergo consecutive and intramolecular reactions to form the heterocycles. In general, this study revealed that the enhanced ionic strength and prolonged reaction time had the promotion effect on the light-absorbing SOC formation. It implies that the aldehyde-derived aqueous-phase SOC would contribute more light-absorbing particulate matter in the industrial or populated area where inorganic ions are abundant.

Cannabis sativa: Release of Volatile Organic Compounds (VOCs) Affecting Air Quality

This review paper highlights about the emission of volatile organic compounds (VOCs) of Cannabis plants. Volatile organic compounds (VOCs) are a large group of chemicals harmful to human health that are readily released into the atmosphere and participate in atmospheric photochemical reactions. Floral Volatile organic compounds (VOCs) are often involved in defence and pollinator attraction. Cannabis cultivation and consumption may lead to additional environmental impacts. Studies found out that Cannabis plants emit a significant amount of biogenic volatile organic compounds (BVOCs) which could cause indoor air quality issues. Indoor Cannabis cultivation is energy-consuming, mainly due to heating, ventilation, air conditioning, and lighting. Energy consumption leads to greenhouse gas emissions. Common compounds to all the tested hemp cultivars include β-myrcene, ϒ-caryophyllene, α-pinene, β-pinene and limonene, reflecting species specificity in the emission of these compounds. β-Myrcene was the most abundant compound in most of the outside hemp cultivars. The terpenes had an earthy musky, and fruity smell may contribute to the odour in Cannabis samples at the vegetative stage, flowering stage, and drying/curing stage. All hemp cultivars are the prolific emitters of terpenoids. The oxidation of highly reactive Biogenic Volatile organic compounds (BVOCs) from Cannabis plants can lead to the formation of ozone and secondary Volatile organic compounds (VOCs) (e.g., formaldehyde and acrolein). In hemp production, considerable odorous emissions occur during field retting. However, more research is needed to address how outdoor air quality is influenced by Cannabis cultivation facilities (CCFs) emissions.

Analysis of the overall potential for electricity production from farm animals manure in Bulgaria

The increasing energy demand combined with the policies for environmental protection are prerequisite to combine them both into the circular economy conception. The utilization of organic waste which produce greenhouse gases during its disposing through production of electricity by obtained secondary organic compounds is a promising approach for the simultaneously meeting of energy needs and decreasing of carbon footprint from the industry. The successful integration of such technology with well-defined economical and technological benefits is optimization task at local level for each country, city or area. An initial evaluation of the potential of manure generated from farm animals in Bulgaria to be utilized as energy source as a different approach for its treatment to reduce the local generation of greenhouse gases is performed in this study. The well-known and commercialized technology for production of biogas from manure by digestion in biogas reactors where at different treatment conditions could be obtained gas mixtures with up to 65 vol. % content of methane is used. The main challenges in front of the implementation of this technology is the impossibility to collect all of the produced manure and also the high transportation costs for its utilization at a centralized site for biogas production and thereafter its combustion in a large power plant. A conservative analysis of the manure quantity available for utilization from different livestock animals and poultry in Bulgaria is performed based on the statistical data for the available farms and the share of free grazing animals. The contribution of different animals to the biogas production and the calorific value based on the gas mixture content are calculated in details. Unlike most other green energy technologies, this one is characterized by 24-hour availability and according to the calculated data a power plant of 1500 MW thermal power could be realized. The reduction of greenhouse gases emissions and potentially spared CO2 emissions quotas at country level are also calculated. As additionally noted there is a secondary commercial product of the anaerobic manure treatment in bioreactors, the solid residue which is applicable as fertilizer for plants due to its high nutritional value.

The Effect of Human Occupancy on Indoor Air Quality through Real-Time Measurements of Key Pollutants.

The primarily emitted compounds by human presence, e.g., skin and volatile organic compounds (VOCs) in breath, can react with typical indoor air oxidants, ozone (O3), and hydroxyl radicals (OH), leading to secondary organic compounds. Nevertheless, our understanding about the formation processes of the compounds through reactions of indoor air oxidants with primary emitted pollutants is still incomplete. In this study we performed real-time measurements of nitrous acid (HONO), nitrogen oxides (NOx = NO + NO2), O3, and VOCs to investigate the contribution of human presence and human activity, e.g., mopping the floor, to secondary organic compounds. During human occupancy a significant increase was observed of 1-butene, isoprene, and d-limonene exhaled by the four adults in the room and an increase of methyl vinyl ketone/methacrolein, methylglyoxal, and 3-methylfuran, formed as secondary compounds through reactions of OH radicals with isoprene. Intriguingly, the level of some compounds (e.g., m/z 126, 6-methyl-5-hepten-2-one, m/z 152, dihydrocarvone, and m/z 194, geranyl acetone) formed through reactions of O3 with the primary compounds was higher in the presence of four adults than during the period of mopping the floor with commercial detergent. These results indicate that human presence can additionally degrade the indoor air quality.

Анализ возможностей извлечения органических соединений пивной дробины различными способами

Brewer's spent grain is a brewing industry waste product that contains various valuable biologically active substances. However, polymers can complicate their extraction. This article focuses on innovative extraction methods, including sustainable deep processing that destroys the internal structures of plant matrix. The research objective was to review publications on the sustainable brewer's spent grain processing as a source of secondary raw materials and plant matrix organic compounds.
 The study featured the last 5–10 years of foreign and domestic analytical and technical publications on grain structure and extraction methods.
 Unlike the traditional acidic, alkaline, and enzymatic methods of grain processing, physical and mechanical methods aim at extracting biogenic peptides, phenolic compounds, and fatty acids. The nature of the processing depends on the type of the extracted compound. Thus, for the extraction of reducing compounds intended for sorption, exposure to high temperatures (≥ 150°C) is the most effective method. A combined treatment with acids or alkalis of the cellulose-lignin complex makes it possible to achieve a 76.2% yield of hemicelluloses. Acid hydrolysis of arabinoxylans is effective at 120–160°C. Alkaline hydrolysis combined with physical treatment makes it possible to reach 60% of arabinoxylans in a mix with phenolic compounds. When extracting nitrogen-containing, phenolic, and lipid compounds, the degree of grinding of the biomaterial and the organic solvent is of great importance. The optimal degree makes it possible to preserve the spatial structure while maintaining a high yield (86%) of organic compounds. Ultrafiltration concentrates the isolated biogenic compound and preserves its activity with a high yield of up to 95%.
 The analysis proved that the brewer's spent grain processing can be both feasible and environmentally friendly. It produces a high yield of pure organic compounds, e.g., peptides, phenolic compounds, fatty acids, etc.

Modern aspects of the use of natural polyphenols in tumor prevention and therapy.

Polyphenols are secondary plant metabolites or organic compounds synthesized by them. In other words, these are molecules that are found in plants. Due to the wide variety of polyphenols and the plants in which they are found, these compounds are divided according to the source of origin, the function of the polyphenols, and their chemical structure; where the main ones are flavonoids. All the beneficial properties of polyphenols have not yet been studied, since this group of substances is very extensive and diverse. However, most polyphenols are known to be powerful antioxidants and have anti-inflammatory effects. Polyphenols help fight cell damage caused by free radicals and immune system components. In particular, polyphenols are credited with a preventive effect that helps protect the body from certain forms of cancer. The onset and progression of tumors may be related directly to oxidative stress, or inflammation. These processes can increase the amount of DNA damage and lead to loss of control over cell division. A number of studies have shown that oxidative stress uncontrolled by antioxidants or an uncontrolled and prolonged inflammatory process increases the risk of developing sarcoma, melanoma, and breast, lung, liver, and prostate cancer. Therefore, a more in-depth study of the effect of polyphenolic compounds on certain signaling pathways that determine the complex cascade of oncogenesis is a promising direction in the search for new methods for the prevention and treatment of tumors.

Investigation of dicarboxylic acids, oxocarboxylic acids, α-dicarbonyls, and volatile organic compounds at the Yellow River Delta, northern China during summer: Contributions of anthropogenic hydrocarbons to secondary organic aerosols

Total suspended particulate (TSP) and air samples were collected at Yellow River Delta (YelRD) in summer 2016 to analyze the concentrations of diacids and related secondary organic aerosols (SOA) and volatile organic compounds (VOCs). 37 organic components (dicarboxylic acids, oxocarboxylic acids, α-dicarbonyls, and fatty acids) and 40 VOCs were analyzed. Most of the dicarboxylic acids showed a similar diurnal variation characteristic with a slightly higher concentration during the daytime than nighttime. Oxalic acid (C2) was the species with the highest contribution to the total dicarboxylic acids, followed by succinic acid (C4), phthalic acid (Ph), and malonic acid (C3). The concentration of total VOCs in YelRD was lower than that in some urban areas in China, alkanes were the dominant component. The oxidation of anthropogenic aromatics to dicarboxylic acids and related SOA is also likely in YelRD. Source apportionment by positive matrix factorization (PMF) revealed that biogenic emissions, diesel exhaust, and oil volatilization, vehicular emissions, coal combustion, and secondary oxidation were the most important sources of organic species and VOCs in YelRD. This study provides potential insights into the characteristics of dicarboxylic acids and related SOA formed from VOCs oxidation in YelRD.

Tracing the Formation of Secondary Aerosols Influenced by Solar Radiation and Relative Humidity in Suburban Environment

AbstractSecondary particulate matter exerts adverse effects on air quality and human health. The production or reaction rate of secondary aerosols in polluted environments remains uncertain and is complicated by diverse emissions and meteorological conditions. By concurrently measuring the mass spectra of compounds in both particulate (using an aerosol mass spectrometer) and gas phases (using proton‐transfer‐reaction mass spectrometry) in suburban Beijing, we linked the secondary organic aerosol (OA) and volatile organic compounds (VOCs) to photochemical age (tage) and obtained their reaction or production rates. Factorization analysis of the mass spectra of OA and the 108 VOC species resolved three oxygenated OAs (OOA) and three secondary VOC factors at different oxidation levels. Primary organic aerosols and VOCs from traffic sources were determined to be important sources for secondary aerosol formation. At high pollution levels under the conditions of weaker solar radiation and higher relative humidity, moderately oxygenated OA (O/C = 0.61) and secondary inorganics were coproduced in combination with rapid consumption of all VOCs. At lower pollution levels, the intense solar radiation caused substantial and rapid production of OOA (O/C = 0.81) and intermediate VOCs (both in a high oxidation state) at a rate of 15.0% h−1 and 14.0% h−1, respectively. These results highlight the feedback effects between radiation and moisture in terms of altering the formation mechanism of secondary aerosols. In particular, highly oxygenated secondary airborne products under strong radiation should be considered in regard to their environmental impact.

Chemical characterization, formation mechanisms and source apportionment of PM2.5 in north Zhejiang Province: The importance of secondary formation and vehicle emission

PM2.5 affects air quality, therefore, chemical evolution, formation mechanism and source identification of PM2.5 are essential to help figure out mitigation measures. PM2.5 and its constituents were comprehensively characterized with highly time-resolved measurements from 2019 to 2020 in north Zhejiang Province (Shanxi, SX) for the first time, with an emphasis on the contribution of secondary formation and vehicle emission to PM2.5. Secondary inorganic ions (sulfate: 3.86 μg/m3, nitrate: 7.82 μg/m3 and ammonium: 4.59 μg/m3, SNA) were found to be the major components (54%) in PM2.5 (29.70 μg/m3). The highly consistence of nitrate, sulfate and secondary organic compounds (SOC) with Ox (NO2 + O3) or RH indicated the importance of photochemical oxidation and heterogeneous reaction in different scenarios. Higher atmospheric oxidative potential facilitated the SOC formation in spring. The PM2.5 mass was apportioned to eight sources resolved by positive matrix factorization (PMF): secondary nitrate (9.63 μg/m3), secondary sulfate (5.14 μg/m3), vehicle emission (7.26 μg/m3), coal combustion (2.39 μg/m3), biomass burning (1.38 μg/m3), soil dust (0.86 μg/m3), industry emission (0.50 μg/m3), and ship emission (0.32 μg/m3). Secondary nitrate (35%) and sulfate (19%) formation and vehicle emission (26%) were the main factors contributing to the PM2.5. Furthermore, the contribution of secondary nitrate formation increased with elevating PM2.5 concentration. Regional transport was synthetically studied by chemical and backward trajectory analysis, reflecting that secondary nitrate contributed severely to the air quality at SX, while vehicle emission contribution enhanced when atmosphere was stagnant. This study first provides long-term comprehensive chemical characterization and source apportionments of PM2.5 pollution in north Zhejiang, which may provide some guidance for the air pollution control.

Effects of the sample matrix on the photobleaching and photodegradation of toluene-derived secondary organic aerosol compounds

Abstract. Secondary organic aerosol (SOA) generated from the photooxidation of aromatic compounds in the presence of oxides of nitrogen (NOx) is known to efficiently absorb ultraviolet and visible radiation. With exposure to sunlight, the photodegradation of chromophoric compounds in the SOA causes this type of SOA to slowly photobleach. These photodegradation reactions may occur in cloud droplets, which are characterized by low concentrations of solutes, or in aerosol particles, which can have highly viscous organic phases and aqueous phases with high concentrations of inorganic salts. To investigate the effects of the surrounding matrix on the rates and mechanisms of photodegradation of SOA compounds, SOA was prepared in a smog chamber by photooxidation of toluene in the presence of NOx. The collected SOA was photolyzed for up to 24 h using near-UV radiation (300–400 nm) from a xenon arc lamp under different conditions: directly on the filter, dissolved in pure water, and dissolved in 1 M ammonium sulfate. The SOA mass absorption coefficient was measured as a function of irradiation time to determine photobleaching rates. Electrospray ionization high-resolution mass spectrometry coupled to liquid chromatography separation was used to observe changes in SOA composition resulting from the irradiation. The rate of decrease in SOA mass absorption coefficient due to photobleaching was the fastest in water, with the presence of 1 M ammonium sulfate modestly slowing down the photobleaching. By contrast, photobleaching directly on the filter was slower. The high-resolution mass spectrometry analysis revealed an efficient photodegradation of nitrophenol compounds on the filter but not in the aqueous phases, with relatively little change observed in the composition of the SOA irradiated in water or 1 M ammonium sulfate despite faster photobleaching than in the on-filter samples. This suggests that photodegradation of nitrophenols contributes much more significantly to photobleaching in the organic phase than in the aqueous phase. We conclude that the SOA absorption coefficient lifetime with respect to photobleaching and lifetimes of individual chromophores in SOA with respect to photodegradation will depend strongly on the sample matrix in which SOA compounds are exposed to sunlight.

Hourly organic tracers-based source apportionment of PM2.5 before and during the Covid-19 lockdown in suburban Shanghai, China: Insights into regional transport influences and response to urban emission reductions

During the Covid-19 outbreak, strict lockdown measures led to notable reductions in transportation-related emissions and significantly altered atmospheric pollution characteristics in urban and suburban areas. In this work, we compare comprehensive online measurements of PM2.5 major components and organic molecular markers in a suburban location in Shanghai, China before lockdown (Dec. 28, 2019 to Jan. 23, 2020) and during lockdown (Jan. 24 to Feb. 9, 2020). The NOx levels declined sharply by 59% from 44 to 18 ppb during the lockdown, while O3 rose two times higher to 42 ppb. The PM2.5 level dropped from 64 to 49 μg m−3 (−24%). The major components all showed reductions, with the reduction of nitrate most prominent at −58%, followed by organics at −19%, and sulfate at −17%. Positive matrix factorization analysis identifies fourteen source factors, including nine primary sources and five secondary sources. The secondary sources consist of sulfate-rich factor, nitrate-rich factor, and three secondary organic aerosol (SOA) factors, with SOA_I being anthropogenic SOA, SOA_II associated with later generation products of organic oxidation, and SOA_III being biogenic SOA. The combined secondary sources contributed to 69% and 63% (40 and 22 μg m−3) of PM2.5 before and during lockdown, respectively, among which the reductions in the nitrate-rich (−55%) factor was the most prominent. Among primary sources, large reductions (>80%) were observed in contributions from industrial, cooking, and vehicle emissions. Unlike some studies reporting that the restriction during the Covid-19 resulted in enhanced secondary sulfate and SOA formation, we observed decreases in both secondary inorganic and SOA formation despite the overall elevated oxidizing capacity in the suburban site. Our results indicate that the formation change in secondary inorganic and organic compounds in response to substantial reductions in urban primary precursors are different for urban and suburban environments.

VOC characteristics and their source apportionment in a coastal industrial area in the Yangtze River Delta, China

Volatile organic compounds (VOCs) are important precursors of secondary organic compounds and ozone, which raise major environmental concerns. To investigate the VOC emission characteristics, measurements of VOCs based on proton transfer reaction-mass spectrometry during 2017 were conducted in a coastal industrial area in Ningbo, Zhejiang Province, China. Based on seasonal variation in species concentration, the positive matrix factorization (PMF) receptor model was applied to apportion the sources of VOCs in each season. The PMF results revealed that unknown acetonitrile source, paint solvent, electronics industry, biomass burning, secondary formation and biogenic emission were mainly attributed to VOC pollution. Biomass burning and secondary formation were the major sources of VOCs and contributed more than 70% of VOC emissions in spring and autumn. Industry-related sources contributed 8.65%–31.2% of the VOCs throughout the year. The unknown acetonitrile source occurred in winter and spring, and contributed 7.6%–43.73% of the VOC emissions in the two seasons. Conditional probability function (CPF) analysis illustrated that the industry sources came from local emission, while biomass burning and biogenic emission mainly came from the northwest direction. The potential source contribution function (PSCF) model showed that secondary formation-related source was mainly from Jiangsu Province, northeastern China and the surrounding ocean. The potential source areas of unknown acetonitrile source were northern Zhejiang Province, southern Jiangsu Province and the northeastern coastal marine environments.

Molecular characterization of nitrogen-containing organic compounds in the winter North China Plain

The molecular characteristics of organic aerosols (OAs) in heavily polluted areas affected by coal combustion (CC) were investigated. In terms of relative abundance, the total nitrogen-containing organic compounds (NOC) accounted for about 61%–68% of all molecules detected in methanol-soluble organic carbon (MSOC) by LC − Q-TOF − MS. More than 85% of the CHON- formulas are nitro-aromatic compounds, which are generally considered to be secondary organic compounds, as evidenced by the lower degree of overlap of these substances in the atmospheric samples and CC samples. Some polycyclic aromatic compounds with 4 N and 1–2O and very low H/C and O/C ratio produced by CC are unstable and easily react to form compounds with higher degrees of saturation. Almost all of the CHON+ homologues detected in the CC samples were also found in the atmospheric samples, indicating that the large amount of CHON+ compounds produced by CC are stable during atmospheric processes. The CHN+ compounds produced by CC contain a certain amount of highly unsaturated compounds, among which 1 N-containing polycyclic aromatic hydrocarbons (1 N-PAHs) is stable in atmosphere and can serve as markers of CC.