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Quantifying differences in secondary organic aerosols (SOAs) between the preindustrial period and the present day is crucial to assess climate forcing and environmental effects resulting from anthropogenic activities. The lack of vegetation information for the preindustrial period and the uncertainties in describing SOA formation are two leading factors preventing simulation of SOA. This study calculated the online emissions of biogenic volatile organic compounds (VOCs) in the Aerosol and Atmospheric Chemistry Model of the Institute of Atmospheric Physics (IAP-AACM) by coupling the Model of Emissions of Gases and Aerosols from Nature (MEGAN), where the input vegetation parameters were simulated by the IAP Dynamic Global Vegetation Model (IAP-DGVM). The volatility basis set (VBS) approach was adopted to simulate SOA formation from the nontraditional pathways, i.e., the oxidation of intermediate VOCs and aging of primary organic aerosol. Although biogenic SOAs (BSOAs) were dominant in SOAs globally in the preindustrial period, the contribution of nontraditional anthropogenic SOAs (ASOAs) to the total SOAs was up to 35.7%. In the present day, the contribution of ASOAs was 2.8 times larger than that in the preindustrial period. The contribution of nontraditional sources of SOAs to SOA was as high as 53.1%. The influence of increased anthropogenic emissions in the present day on BSOA concentrations was greater than that of increased biogenic emission changes. The response of BSOA concentrations to anthropogenic emission changes in the present day was more sensitive than that in the preindustrial period. The nontraditional sources and the atmospheric oxidation capability greatly affect the global SOA change. [ABSTRACT FROM AUTHOR]

The oxidative potential (OP) of particulate matter has been widely suggested as a key metric for describing atmospheric particle toxicity. Secondary organic aerosol (SOA) and redox-active transition metals, such as iron and copper, are key drivers of particle OP. However, their relative contributions to OP, as well as the influence of metal-organic interactions and particulate chemistry on OP, remains uncertain. In this work, we simultaneously deploy two novel online instruments for the first time, providing robust quantification of particle OP. We utilize online AA (OPAA) and 2,7-dichlorofluoroscein (ROSDCFH) methods to investigate the influence of Fe(II) and Cu(II) on the OP of secondary organic aerosol (SOA). In addition, we quantify the OH production (OPOH) from these particle mixtures. We observe a range of synergistic and antagonistic interactions when Fe(II) and Cu(II) are mixed with representative biogenic (β-pinene) and anthropogenic (naphthalene) SOA. A newly developed kinetic model revealed key reactions among SOA components, transition metals, and ascorbate, influencing OPAA. Model predictions agree well with OPAA measurements, highlighting metal-ascorbate and -naphthoquinone-ascorbate reactions as important drivers of OPAA. The simultaneous application of multiple OP assays and a kinetic model provides new insights into the influence of metal and SOA interactions on particle OP.

Biogenic volatile organic compounds (BVOCs) are important precursors of forming ozone (O3) and secondary organic aerosols (SOAs), which have important impacts on air quality and climate change. Using a literature search, this review analyzed the concentration levels and spatial-temporal distributions of isoprene and monoterpene in the atmosphere in China, mainly from biogenic emissions, and estimated their impact on O3 and SOA generation. The existing observations were mainly in the Beijing–Tianjin–Hebei region, the Pearl River Delta region, central China, and in remote mountainous areas. The results showed that isoprene is the dominant component of BVOCs in the atmosphere, and its ambient concentration is much higher than monoterpene. The site-average concentrations of isoprene and monoterpene were 0.004–3.80 and 0.0003–6.31 ppb, respectively. At vegetation sites, the concentrations of isoprene and monoterpene were 0.006–3.80 and 0.007–6.31 ppb, respectively, whereas they were 0.004–2.70 and 0.0003–1.10 ppb at urban sites. For urban sites, the higher concentrations of annual isoprene occurred mainly in several central megacities, in the Sichuan–Chongqing region, and in southern regions. For vegetation sites, higher concentrations mainly occurred in southern regions. Ambient concentrations of BVOCs in the western region were the lowest for both urban and vegetation sites. Both isoprene and monoterpene showed higher concentrations in summer. The potential of isoprene and monoterpene to form O3 was 0.05–57.21 and 0.003–72.35 ppb, while that which form SOA was 0.0002–0.21 and 0.0006–10.46 µg/m3, respectively. For urban sites, the average annual O3 formation potential (OFP) by isoprene and monoterpene was 8.70 and 2.58 ppb, respectively, and their SOA formation potential (SOAP) was 0.03 and 0.37 µg/m3, respectively. For vegetation sites, it was 7.95 and 5.31 ppb and 0.03 and 0.75 µg/m3, respectively. The annual average contributions of isoprene and monoterpene to O3 and SOA formation were higher in the Beijing–Tianjin–Hebei region, Pearl River Delta region, and central China, which experience severe air pollution in China. [ABSTRACT FROM AUTHOR]

During the period 2019–2020, size‐segregated aerosol samples containing elemental and organic carbon (EC and OC) were investigated. These samples were collected weekly using an eight‐stage cascade impactor from an urban site located at Aksaray University, Aksaray. The quantification of EC and OC was carried out through a thermal‐optical transmission device. The results revealed consistent size distribution attributes of EC and OC between winter and summer. Although EC accounted for an insignificant percentage (4.4%) of particulate matter (PM) in the PM9.0–10.0 fraction during winter, a more substantial portion of OC in the same fraction (13.4%) comprised EC. Seasonal variations were distinct for EC but not significant for OC. Strong correlations between OC and EC were observed in coarse particle fractions, indicating a common source, with weaker correlations in fine particles. The highest OC/EC ratio was in the PM0.43–0.65 fraction, followed by PM2.1–3.3. The ratio of OC to EC in fine PM exceeded the threshold of 15 consistently. The observation indicates that as particle size increases, there is a noticeable decline in the OC to EC ratios. Secondary organic aerosols (SOA) accounted for 60.8% (winter) and 89.8% (summer) of OC values, emphasizing the substantial impact of SOA on Aksaray's atmosphere. Both seasons exhibited a multimodal distribution of ambient OC. In winter, the EC distribution was dominated by fine particles, with a bimodal pattern (PM1.1–2.1 and PM0.43–0.65 peaks). Common pollutant sources, including traffic emissions, road dust, biogenic emissions, and coal combustion, were identified for both seasons in coarse and fine particle fractions. These findings underscore the importance of emission control strategies targeting fine PM in Aksaray. [ABSTRACT FROM AUTHOR]

Organic vapors from biomass burning are a major source of secondary organic aerosols (SOAs). Previous smog chamber studies found that the SOA contributors in biomass-burning emissions are mainly volatile organic compounds (VOCs). While intermediate volatility organic compounds (IVOCs) are efficient SOA precursors and contribute a considerable fraction of biomass-burning emissions, their contribution to SOA formation has not been directly observed. Here, by deploying a newly-developed oxidation flow reactor to study SOA formation from wood burning, we find that IVOCs can contribute ∼70% of the formed SOA, i.e. >2 times more than VOCs. This previously missing SOA fraction is interpreted to be due to the high wall losses of semi-volatile oxidation products of IVOCs in smog chambers. The finding in this study reveals that SOA production from biomass burning is much higher than previously thought, and highlights the urgent need for more research on the IVOCs from biomass burning and potentially other emission sources. [ABSTRACT FROM AUTHOR]

Secondary organic aerosol (SOA) plays a critical, yet uncertain, role in air quality and climate. Once formed, SOA is transported throughout the atmosphere and is exposed to solar UV light. Information on the viscosity of SOA, and how it may change with solar UV exposure, is needed to accurately predict air quality and climate. However, the effect of solar UV radiation on the viscosity of SOA and the associated implications for air quality and climate predictions is largely unknown. Here, we report the viscosity of SOA after exposure to UV radiation, equivalent to a UV exposure of 6 to 14 d at midlatitudes in summer. Surprisingly, UV-aging led to as much as five orders of magnitude increase in viscosity compared to unirradiated SOA. This increase in viscosity can be rationalized in part by an increase in molecular mass and oxidation of organic molecules constituting the SOA material, as determined by high-resolution mass spectrometry. We demonstrate that UV-aging can lead to an increased abundance of aerosols in the atmosphere in a glassy solid state. Therefore, UV-aging could represent an unrecognized source of nuclei for ice clouds in the atmosphere, with important implications for Earth's energy budget. We also show that UV-aging increases the mixing times within SOA particles by up to five orders of magnitude throughout the troposphere with important implications for predicting the growth, evaporation, and size distribution of SOA, and hence, air pollution and climate.

Elucidating the effects of anthropogenic pollutants on the photooxidation of biogenic volatile organic compounds is crucial to understanding the fundamental mechanisms of secondary organic aerosol (SOA) formation. Here, the impacts of NO 2 and SO 2 on SOA formation from the photooxidation of a representative monoterpene, β -pinene, were investigated by a number of laboratory studies. The results indicated NO 2 enhanced the SOA mass concentrations and particle number concentrations under both low and high β -pinene conditions. This could be rationalized that the increased O 3 concentrations upon the NO x photolysis was helpful for the generation of more amounts of O 3 -oxidized products, which accelerated the SOA nucleation and growth. Combing with NO 2 , the promotion of the SOA yield by SO 2 was mainly reflected in the increase of mass concentration, which might be due to the elimination of the newly formed particles by the initially formed particles. The observed low oxidation degree of SOA might be attributed to the fast growth of SOA, resulting in the uptake of less oxygenated gas-phase species onto the particle phase. The present findings have important implications for SOA formation affected by anthropogenic–biogenic interactions in the ambient atmosphere. [Display omitted] [ABSTRACT FROM AUTHOR]

The environmental quality of the outdoor, as well as the health of people and animals, might be impacted by the total volatile organic compounds (TVOC), NH3, and H2S from pig houses. The amount of study on the features of VOC and smell emission from pig fattening process locations is rather limited, and the assessment of the primary odor-causing compounds and health hazards is unclear; inadequate investigation has been done for the generation of ozone and secondary organic aerosols. In this study, a portable odor meter was employed to measure odor levels and analyze the sources of odor at four different locations within the pigsty. Specific VOCs were collected using a Suma tank to determine the magnitude of odor, assess the formation of SOA and OFP, and evaluate associated health risks. Furthermore, online monitoring sensors were utilized to detect fluctuations in TVOC, H2S, and NH3 concentrations. Results showed that TVOC emissions outside the house were prominent in November and January, while inside the house, they were concentrated in December, with a maximum of 60,000 μg·m−3, with an overall decreasing trend. H2S emissions were low, almost zero, and NH3 emissions showed a stable trend throughout the season, with a peak of 29.3 μg·m−3 in mid-January. A total of 36 VOCs were detected, with the highest concentrations of acetaldehyde and undecane at 34.5 and 34.8 μg·m−3, respectively, and the main odor-causing substances were acetaldehyde, NH3, and H2S; OFP contributed most to acetaldehyde and SOA contributed most to aromatic hydrocarbons and alkanes. This research endeavor establishes a scientifically grounded framework for mitigating malodors and determining an optimal treatment methodology. [ABSTRACT FROM AUTHOR]

Furans are a major class of volatile organic compounds emitted from biomass burning. Their high reactivity with atmospheric oxidants leads to the formation of secondary organic aerosol (SOA), including secondary brown carbon (BrC) that can affect global climate via interactions with solar radiation. Here, we investigate the optical properties and chemical composition of SOA generated via photooxidation of furfural, 2‐methylfuran, and 3‐methylfuran under dry (RH < 5%) and humid (RH ∼ 50%) conditions in the presence of nitrogen oxides (NOx) and ammonium sulfate seed aerosol. Dry furfural oxidation has the greatest BrC formation, including reduced nitrogen‐containing organic compounds (NOCs) in SOA, which are dominated by amines and amides formed from reactions between carbonyls and ammonia/ammonium. Based on the products detected, we propose novel formation pathways of NOCs in furfural photooxidation, which can contribute to BrC via accretion reactions during the photochemical aging of biomass burning plumes. Plain Language Summary: Biomass burning is a substantial source of both gas‐ and particle‐phase carbon to the atmosphere, including light‐absorbing aerosol known as brown carbon. Brown carbon can be emitted directly from combustion activities and also formed through the oxidation of gas‐phase carbon, known as secondary brown carbon. In this study, we investigate secondary brown aerosol formation from furans (chemicals with a five‐membered aromatic ring with four carbon atoms and one oxygen atom), one of the major classes of gaseous compounds emitted from biomass burning. We find that furfural is an important subset of furans that generates substantial brown carbon during oxidation, with corresponding formation of nitrogen‐containing organic compounds. Key Points: Photooxidation of furans in the presence of NOx and ammonium sulfate aerosol leads to secondary brown carbon formationOptical properties of secondary brown carbon from furfural photooxidation are comparable to ambient biomass burning observationsReduced nitrogen species are associated with brown carbon formation from furfural photooxidation and are enhanced under dry conditions [ABSTRACT FROM AUTHOR]

In this study, we reviewed smog chamber systems and methodologies used in secondary organic aerosol (SOA) formation studies. Many important chambers across the world have been reviewed, including 18 American, 24 European, and 8 Asian chambers. The characteristics of the chambers (location, reactor size, wall materials, and light sources), measurement systems (popular equipment and working principles), and methodologies (SOA yield calculation and wall-loss correction) are summarized. This review discussed key experimental parameters such as surface-to-volume ratio (S/V), temperature, relative humidity, light intensity, and wall effect that influence the results of the experiment, and how the methodologies have evolved for more accurate simulation of atmospheric processes. In addition, this review identifies the sources of uncertainties in finding SOA yields that are originated from experimental systems and methodologies used in previous studies. The intensity of the installed artificial lights (photolysis rate of NO2 varied from 0.1/min to 0.40/min), SOA density assumption (varied from 1 g/cm3 to 1.45 g/cm3), wall-loss management, and background contaminants were identified as important sources of uncertainty. The methodologies developed in previous studies to minimize those uncertainties are also discussed. [ABSTRACT FROM AUTHOR]

To determine the complex refractive indices of aerosol particles in the atmospheric boundary layer, simultaneous measurements of scattering coefficients at 450, 550, and 700 nm wavelengths, absorption coefficient at 565 nm, and aerosol particle number size distributions were performed during a voyage of the icebreaker Shirase from Tokyo to the offing of the Philippines over the northwestern Pacific in November 2010. Three sets of Ångström exponents were calculated using the three observed scattering coefficients. Using the observed number size distributions, three sets of Ångström exponents were reproduced by assuming their complex refractive indices. Appropriate complex refractive indices for aerosol particles in the atmospheric boundary layer can be obtained when the difference between the observed and reproduced Ångström exponents is minimal. Absorbing substances were assumed to be present in the fine particles. For polluted air masses, if the refractive index for aerosol particles was uniform regardless of the particle size, the estimated Ångström exponents were consistent with the observed values. The refractive index must be the normal dispersion, which increases with a decrease in wavelength. For pristine air masses, the refractive index was estimated to be higher for coarse particles than for fine particles. This could be explained by preferential condensation of organic compounds onto coarse particles, which is observed to alter the number size distribution over Chichi-jima of the Ogasawara Islands in the northwestern Pacific in August 2014 and February 2015. This study is the first to report that the increase in the refractive index of coarse particles is likely caused by the optical properties of volatile organic compounds and/or secondary organic aerosols condensed on coarse particles. [ABSTRACT FROM AUTHOR]

This review article delves into the multifaceted relationship between climate change, air quality, and respiratory health, placing a special focus on the process of particle deposition in the lungs. We discuss the capability of climate change to intensify air pollution and alter particulate matter physicochemical properties such as size, dispersion, and chemical composition. These alterations play a significant role in influencing the deposition of particles in the lungs, leading to consequential respiratory health effects. The review paper provides a broad exploration of climate change's direct and indirect role in modifying particulate air pollution features and its interaction with other air pollutants, which may change the ability of particle deposition in the lungs. In conclusion, climate change may play an important role in regulating particle deposition in the lungs by changing physicochemistry of particulate air pollution, therefore, increasing the risk of respiratory disease development. Climate change influences particle deposition in the lungs by modifying the physicochemical properties of particulate air pollution, thereby escalating the risk of respiratory disease development. It is crucial for healthcare providers to educate patients about the relationship between climate change and respiratory health. People with conditions such as asthma, COPD, and allergies must understand how changes in weather, air pollution, and allergens can exacerbate their symptoms. Instruction on understanding air quality indices and pollen predictions, along with recommendations on adapting everyday activities and medication regimens in response, is essential. [ABSTRACT FROM AUTHOR]

The impact of relative humidity (RH) on organic new particle formation (NPF) from the ozonolysis of biogenic volatile organic compounds (BVOCs) remains an area of active debate. Previous reports provide contradictory results, indicating both the depression and enhancement of NPF under conditions of high RH. Herein, we report on the impact of RH on NPF from the dark ozonolysis of cis-3-hexenyl acetate (CHA), a green-leaf volatile (GLV) emitted by vegetation. We show that RH inhibits NPF by this BVOC, essentially shutting it down at RH levels > 1%. While the mechanism for the inhibition of NPF remains unclear, we demonstrate that it is likely not due to increased losses of CHA to the humid chamber walls. New oxidation products dominant under humid conditions are proposed that, based on estimated vapor pressures (VPs), should enhance NPF; however, it is possible that the vapor phase concentration of these low-volatility products is not sufficient to initiate NPF. Furthermore, the reaction of C3-excited state Criegee intermediates (CIs) with water may lead to the formation of small carboxylic acids that do not contribute to NPF. This hypothesis is supported by experiments with quaternary O3 + CHA + α-pinene + RH systems, which showed decreases in total α-pinene-derived NPF at ~0% RH and subsequent recovery at elevated RH. [ABSTRACT FROM AUTHOR]

Abstract Furans are a major class of volatile organic compounds emitted from biomass burning. Their high reactivity with atmospheric oxidants leads to the formation of secondary organic aerosol (SOA), including secondary brown carbon (BrC) that can affect global climate via interactions with solar radiation. Here, we investigate the optical properties and chemical composition of SOA generated via photooxidation of furfural, 2‐methylfuran, and 3‐methylfuran under dry (RH

AbstractThis review article delves into the multifaceted relationship between climate change, air quality, and respiratory health, placing a special focus on the process of particle deposition in the lungs. We discuss the capability of climate change to intensify air pollution and alter particulate matter physicochemical properties such as size, dispersion, and chemical composition. These alterations play a significant role in influencing the deposition of particles in the lungs, leading to consequential respiratory health effects. The review paper provides a broad exploration of climate change’s direct and indirect role in modifying particulate air pollution features and its interaction with other air pollutants, which may change the ability of particle deposition in the lungs. In conclusion, climate change may play an important role in regulating particle deposition in the lungs by changing physicochemistry of particulate air pollution, therefore, increasing the risk of respiratory disease development.

Organic aerosol (OA) is a major component of atmospheric particulate matter (PM) with complex composition and formation processes influenced by various factors. Emission reduction can alter both precursors and oxidants which further affects secondary OA formation. Here we provide an observational analysis of secondary OA (SOA) variation properties in Yangtze River Delta (YRD) of eastern China in response to large scale of emission reduction during Chinese New Year (CNY) holidays from 2015 to 2020, and the COVID-19 pandemic period from January to March, 2020. We found a 17% increase of SOA proportion during the COVID lockdown. The relative enrichment of SOA is also found during multi-year CNY holidays with dramatic reduction of anthropogenic emissions. Two types of oxygenated OA (OOA) influenced by mixed emissions and SOA formation were found to be the dominant components during the lockdown in YRD region. Our results highlight that these emission-reduction-induced changes in organic aerosol need to be considered in the future to optimize air pollution control measures. [ABSTRACT FROM AUTHOR]

Carbonaceous Aerosols (CAs) have played an active role in the Earth's atmospheric system, climate, human health, and radiative forcing. Due to their significant role in the atmosphere, it was imperative to characterize the carbonaceous components [organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and total carbonaceous aerosols (TCA)] of PM2.5 samples collected at three different urban locations (Mohal-Kullu, Almora, and Darjeeling) of the Himalayan region of India during August 2018–December 2019. The annual average mass concentrations of PM2.5 were recorded as 40 ± 27, 27 ± 21, and 38 ± 13 µg m−3 for Mohal-Kullu, Almora, and Darjeeling, respectively, which is near the Indian National Ambient Air Quality Standards (NAAQS) (24 h: 60 µg m-3; annual: 40 µg m−3). The OC/EC ratio and significant correlation of OC with EC and WSOC with OC indicated a substantial effect of biomass burning and secondary organic aerosol formation over the study sites. OC was found to be secondary in nature over the study sites during the study period. The contribution of TCA in PM2.5 showed CAs as a significant contributor to the mass concentration of particulate matter (PM) over the Himalayan regions. HYSPLIT model demonstrates that regionally transported air masses, mostly from Indo-Gangetic plain (IGP), the Thar desert, the semi-arid region, Nepal, and local areas, considerably influence PM concentrations and chemical composition over the pristine Himalayan altitudes. The study implies that to improve the air quality in booming urban areas, it is necessary to pay attention to both local emission sources and meteorological conditions. [ABSTRACT FROM AUTHOR]

Secondary organic aerosol (SOA) produced by atmospheric oxidation of primary emitted precursors is a major contributor to fine particulate matter (PM2.5) air pollution worldwide. Observations during winter haze pollution episodes in urban China show that most of this SOA originates from fossil-fuel combustion but the chemical mechanisms involved are unclear. Here we report field observations in a Beijing winter haze event that reveal fast aqueous-phase conversion of fossil-fuel primary organic aerosol (POA) to SOA at high relative humidity. Analyses of aerosol mass spectra and elemental ratios indicate that ring-breaking oxidation of POA aromatic species, leading to functionalization as carbonyls and carboxylic acids, may serve as the dominant mechanism for this SOA formation. A POA origin for SOA could explain why SOA has been decreasing over the 2013-2018 period in response to POA emission controls even as emissions of volatile organic compounds (VOCs) have remained flat.

Ultrafine particles (UFP) of Secondary Organic Aerosol (SOA) penetrate deep into the human respiratory system and exert fatal effects on human health. However, there is little data on the potential deposited doses of UFP-generated SOA in the human respiratory tract. This study is to estimate the fraction of aerosol deposition using a multiple-path-particle-dosimetry (MPPD) model. For relevancy of real life, the model employed measured concentrations of toluene-derived fresh and aged SOA produced within serially connected smog chamber and PAM-OFR (Potential Aerosol Mass-Oxidation Flow Reactor) under atmospheric environmental conditions (NOx and relative humidity). The number concentrations and chemical composition of fresh and aged aerosols produced within the chambers were measured using Scanning Mobility Particle Sizer (SMPS) and High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS), while the morphology of individual particles was analyzed using Scanning Electron Microscopy (SEM). The number concentration of aged SOA-w/s was more than double compared to that of fresh SOA-w/s (maximum reached after 10 h) with its size less than 100 nm. The O:C ratio for aged SOA-w/s were 0.96 and 1.15 depending on RH (0.96 at 3% RH and 1.15 at 50% RH), and individual spherical particles containing water were present in agglomerates with its size of less than 1 µm. In all inhalable fresh and aged SOA produced in the two chambers, 5–22% of aerosol is deposited in the Head airways, 4–8% in the tracheobronchial, and 8–34% in the alveolar regions. The predominant deposition of the aged aerosol occurred in the alveoli (in the generation 20th lobe), and the deposition faction in the alveoli was 2–3 times higher in the children group than the adults group. This study presented a quantitative exposure assessment of SOA generated under a realistic simulation and suggested the possibility of evaluating long-term exposure to SOA and potential health effects by determining the potential inhalable aerosol doses and the fraction of deposition in the human respiratory system.

Volatile organic compounds (VOCs) emitted by plant foliage play an important role in ozone (O3) and secondary organic aerosol (SOA) formation. Their emissions can be influenced by the leaf age. We explored the VOCs emissions and their effects on the formation of O3 and SOA from plant foliage in different ages. VOCs emissions from the young, mature, and senescent leaves of Ginkgo biloba, Ligustrum lucidum, and Forsythia suspensa were measured using the dynamic enclosure system and the TD–GC–MS technique. Based on the emission rates of quantified compounds, their potential to form O3 and SOA was estimated. Results showed that there were significant differences in the VOCs emission rate and their composition among leaves in different ages. The emission rate of the total VOCs by young leaves was the highest, while the lowest by senescent leaves. Monoterpenes were the dominant VOCs category, and isoprene emission had the lowest contribution for the leaves at each age. With increasing leaf age, the proportion of monoterpenes emission increased, and the proportion of sesquiterpenes decreased. The variations of isoprene and other VOCs were different. The potentials of total VOCs, isoprene, monoterpenes, sesquiterpenes, and other VOCs to form O3 (OFP) and SOA (SOAP) varied significantly among leaves at different ages. The total OFP and SOAP were the highest by young leaves, while the lowest by senescent leaves. With increasing leaf age, the contribution of monoterpenes to OFP and SOAP also increased, while that of sesquiterpenes decreased. Our study will provide support for the more accurate parameterization of the emission model and help to understand the VOCs emissions and study the precise prevention and control of complex air pollution at different times. [ABSTRACT FROM AUTHOR]

Iron ion is the common transition metal ion in atmospheric aerosol, which can affect the components and optics of secondary organic aerosol (SOA). In the current study, the atmospheric photooxidation of toluene to produce SOA in the presence of ferric chloride fine particles is simulated in a smog chamber; on-line and off-line mass spectrometry and spectroscopic instruments are used to characterize constituents and optics of SOA. Compare with SOA formed in the absence of fine particles, the laser desorption/ionization mass spectra of toluene SOA generated in the presence of ferric chloride fine particles show ion peaks of m/z = 163 and 178, the UV-Vis spectra of the extracting solution for toluene SOA have peaks near 400 and 700 nm, and the electrospray ionization mass spectra contain peaks at m/z = 248 and 300. Based on this spectral information, it is shown that gaseous methylcatechol formed from photooxidation of toluene may react with iron ion on the surface of fine particles by complexing and oxidation–reduction, resulting in methylbenzoquinone products and metallo-organic complex ions such as [Fe(III)(CH3C6H3OO)]+, [Fe(III)(CH3C6H3 OO)2]− and [Fe(III)(CH3C6H3OO)Cl2]−. These products have strong light absorption ability, resulting in an increase in the averaged mass absorption coefficient () in the 200~1000 nm range and the MAC at 365 nm (MAC365) for toluene SOA, while and MAC365 progressively increase with an increasing concentration of ferric chloride fine particles. These results serve as experimental references for the study of the formation mechanism and optical properties of metallo-organic complexes in atmospheric aerosol particles in regions experiencing high levels of fine particles of metal and automobile exhaust pollution. [ABSTRACT FROM AUTHOR]

Volatility determines the gas-particle partitioning of organic compounds. Volatility is thus a key property needed to understand the behavior of organic aerosol (OA) in the atmosphere. Various studies have been conducted to experimentally measure and numerically simulate distributions of OA volatility. The observed OA evaporation rates have generally been slower than the rates assuming instantaneous gas-particle equilibrium and volatility estimated from secondary organic aerosol (SOA) formation experiments. Particle-phase diffusion and/or low-volatility compounds, such as oligomers and highly oxygenated molecules, could limit the evaporation of OA, though the relative contributions of these factors are still uncertain. In this study, we conducted model simulations using a volatility basis set framework with the consideration of kinetic gas-particle partitioning, formation and dissociation of dimers, and particle-phase diffusion to reproduce observed evaporative behaviors of SOA formed from α-pinene ozonolysis and 1,3,5-trimethylbenzene (TMB)/NOx photooxidation. Based on simulations constrained by various volatility distributions derived from chemical analysis or heating experiments, we found that both dimerization and slow particle-phase diffusion contributed to the observed slow evaporation under dry conditions. In contrast, particle-phase diffusion did not practically inhibit SOA evaporation under humid conditions. The similarity of the fitted parameters, including dimer formation/dissociation rates and bulk diffusivity, for SOA from α-pinene and 1,3,5-TMB under dry conditions suggested that these processes are important for both monoterpene and aromatic SOA. Evaporation rates of SOA from α-pinene in this study were slower than the rates reported in previous experimental studies. This difference could be partly explained by differences in the experimental setups, including the treatment of organic vapors.

Understanding how gases interact with and are incorporated into atmospheric secondary organic aerosol particles is crucial for predicting particle effects on climate and human health. This work examined how three gaseous organic nitrates (ON) are taken up into viscous particles formed from the ozonolysis of α-pinene (AP). Experiments were performed in a flow reactor at room temperature under dry conditions, either with or without an OH scavenger present, with constant ozone and variable AP concentrations. Each ON was introduced independently into the flow reactor and was present during particle formation/growth. ON gas-phase concentrations were determined by gas chromatography−mass spectrometry, and particle phase concentrations were measured by high-resolution time-of-flight aerosol mass spectrometry. Partition coefficients (KSOA) for each ON were independent of the initial AP concentration, except for 2-ethylhexyl nitrate which was undetectable in the particles at the lowest AP concentration. Measured KSOA values were larger than those previously determined for equilibrium partitioning, which points to a potential burying mechanism for incorporation of ON during particle growth. Estimated effective net uptake coefficients (γΟΝ) were found to increase with initial AP concentration. Concentrations of gas-phase oxidation products (including dimers and autoxidation products) predicted using an updated master chemical mechanism increased with AP concentration, with little change in the overall species distribution, consistent with increased trapping/burying of ON during particle growth and thus increased values of γΟΝ. These results provide further evidence that kinetically controlled burying can contribute significantly to particle growth, provided that the incoming gas-phase molecules have sufficient residence time on the particle surface to become buried via subsequent gas−surface collisions.

Secondary organic aerosol (SOA) represents a major constituent of tropospheric fine particulate matter, with profound implications for human health and climate. However, the chemical mechanisms leading to SOA formation remain uncertain, and atmospheric models consistently underpredict the global SOA budget. Small α-dicarbonyls, such as methylglyoxal, are ubiquitous in the atmosphere because of their significant production from photooxidation of aromatic hydrocarbons from traffic and industrial sources as well as from biogenic isoprene. Current experimental and theoretical results on the roles of methylglyoxal in SOA formation are conflicting. Using quantum chemical calculations, we show cationic oligomerization of methylglyoxal in aqueous media. Initial protonation and hydration of methylglyoxal lead to formation of diols/tetrol, and subsequent protonation and dehydration of diols/tetrol yield carbenium ions, which represent the key intermediates for formation and propagation of oligomerization. On the other hand, our results reveal that the previously proposed oligomerization via hydration for methylglyoxal is kinetically and thermodynamically implausible. The carbenium ion-mediated mechanism occurs barrierlessly on weakly acidic aerosols and cloud/fog droplets and likely provides a key pathway for SOA formation from biogenic and anthropogenic emissions.

Abstract This study divided a basin metropolitan area with high air pollution into three subareas, namely urban, suburban, and rural, on the basis of population density for a systematic analysis of the effects of local air pollutants on respiratory diseases. A panel data regression model was used to estimate the annual incidence growth rates (AIGRs) of the four respiratory diseases, namely lung cancer, chronic obstructive pulmonary disease, asthma, and pneumonia, resulting from exposure to fine particulate matter (PM2.5, diameter of 2.5 μm or less), odd oxygen (ODO), or nonmethane hydrocarbon (NMHC). The results indicate that the prevailing wind direction is not a major factor determining the distribution of air pollutants. The spatial distributions of ODO and NMHC differed from that of PM2.5. Three air pollutants contributed to positive AIGRs of the four diseases in the study area, but PM2.5 which had a negative AIGR for asthma in the rural subarea. The pollutants with the strongest effects on AIGR, in descending order, were NMHC, PM2.5, and ODO. The effect of ambient NMHC was significant and nonnegligible, especially in the urban subarea. A dimensionless potential AIGR (PAIGR) formula was established to quantitatively compare the effects of different air pollutants on the four respiratory diseases. The results indicate that ambient NMHC had the strongest effect on the incidences of the respiratory diseases, followed by that of ambient PM2.5. The effect of ambient NMHC was significant and nonnegligible, especially in the urban subarea. The PAIGR ratio ranges of PM2.5 to ODO and NMHC to ODO for the four diseases in urban subsarea were from 3 to 19 and from 289 to 920, respectively. This study also applied multivariate regression to assess the association among 5 aspects, namely air quality, point source, line source, area source, and socioeconomic status, and the incidences of the four respiratory diseases. The results indicate that the model has favorable fit and can thus reflect the associations of the 15 factors of 5 aspects with the four respiratory diseases in each subarea.

Volatile organic compounds (VOCs) emitted from anthropogenic sources are critical precursors to ozone and secondary organic aerosol (SOA), and potential contributors to health risks. However, quantitatively estimating the impact of these source‐derived VOCs on air quality and health is limited by their diverse chemical compositions, resulting in nonselective mass‐based VOC control strategies. To address this issue, we conducted a comprehensive study of typical VOC samples freshly emitted from various flue gases via field‐based measurements and chemical analysis under the same quality control. Our results showed that different source‐specific VOC profiles have unequal sensitivities to chemical reactivity on ozone and SOA formation potential, as well as potential health risks. Mobile sources and residential solid fuel burning were identified as the most sensitive sources of potential secondary pollutants and potential inhalation health risks, respectively. Despite accounting for only 22.7% of the total mass, residential VOCs contributed significantly to both inhalation non‐cancer risk (NCR) (57.4%) and cancer risk (CR) (47.3%). The large inequality between residential VOC emissions and their health risks highlights the necessity of continuously promoting the transition from mass‐based VOC control to effect‐oriented VOC control. This suggests that mobile sources is worth more attention for secondary pollutant formation, while residential solid fuel burning sources should receive more policy priority to reduce health risks. Plain Language Summary: Volatile organic compounds (VOCs) can not only contribute to secondary pollutant formation but can also directly induce negative human health impacts. However, there is a knowledge gap between source‐emitted VOC chemicals and their potential health risks (including non‐cancer and cancer risks). This study first revealed unequal potential health risks posed by anthropogenic VOCs through real‐world measurements, providing a new perspective to the debate on VOC pollution control. This study conducted systematic field measurements and comprehensive assessments of the potential health risks of source‐emitted VOCs. The results highlight the need for control strategies that consider health‐relevant metrics beyond VOC mass, especially in residential areas where people may be more exposed to these chemicals. Key Points: Residential solid fuel burning (accounting for 23% of total volatile organic compound (VOC) mass) contributes to 57% of the noncancer risk and 47% of the cancer riskAcrolein is the predominant contributor to non‐cancer risk induced by VOCs emitted from the majority of anthropogenic sourcesThe identification of VOC species benefits the promotion of the transition from mass‐based VOC control to effect‐oriented VOC control [ABSTRACT FROM AUTHOR]

The goal of the Sea2Cloud project is to study the interplay between surface ocean biogeochemical and physical properties, fluxes to the atmosphere, and ultimately their impact on cloud formation under minimal direct anthropogenic influence. Here we present an interdisciplinary approach, combining atmospheric physics and chemistry with marine biogeochemistry, during a voyage between 41° and 47°S in March 2020. In parallel to ambient measurements of atmospheric composition and seawater biogeochemical properties, we describe semicontrolled experiments to characterize nascent sea spray properties and nucleation from gas-phase biogenic emissions. The experimental framework for studying the impact of the predicted evolution of ozone concentration in the Southern Hemisphere is also detailed. After describing the experimental strategy, we present the oceanic and meteorological context including provisional results on atmospheric thermodynamics, composition, and flux measurements. In situ measurements and flux studies were carried out on different biological communities by sampling surface seawater from subantarctic, subtropical, and frontal water masses. Air–Sea-Interface Tanks (ASIT) were used to quantify biogenic emissions of trace gases under realistic environmental conditions, with nucleation observed in association with biogenic seawater emissions. Sea spray continuously generated produced sea spray fluxes of 34% of organic matter by mass, of which 4% particles had fluorescent properties, and which size distribution resembled the one found in clean sectors of the Southern Ocean. The goal of Sea2Cloud is to generate realistic parameterizations of emission flux dependences of trace gases and nucleation precursors, sea spray, cloud condensation nuclei, and ice nuclei using seawater biogeochemistry, for implementation in regional atmospheric models. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• The aqueous-phase reactions of typical long-chain alcohols start from initial protonation. • Dehydration to carbenium ions (CBs) is the rate-limiting step. • OSA/OSI and dimers are formed via esterification and oligomerization from CBs, respectively. • Relative short-chain alcohols are more prone to contribute OSAs/OSIs than long-chain alcohols. • Typical long-chain alcohols contribute SOA formation via esterification rather than oligomerization. Organosulfate (OSA) nanoparticles, as secondary organic aerosol (SOA) compositions, are ubiquitous in urban and rural environments. Hence, we systemically investigated the mechanisms and kinetics of aqueous-phase reactions of 1-butanol/1-decanol (BOL/DOL) and their roles in the formation of OSA nanoparticles by using quantum chemical and kinetic calculations. The mechanism results show that the aqueous-phase reactions of BOL/DOL start from initial protonation at alcoholic OH-groups to form carbenium ions (CBs), which engage in the subsequent esterification or oligomerization reactions to form OSAs/organosulfites (OSIs) or dimers. The kinetic results reveal that dehydration to form CBs for BOL and DOL reaction systems is the rate-limiting step. Subsequently, about 18% of CBs occur via oligomerization to dimers, which are difficult to further oligomerize because all reactive sites are occupied. The rate constant of BOL reaction system is one order of magnitude larger than that of DOL reaction system, implying that relative short-chain alcohols are more prone to contribute OSAs/OSIs than long-chain alcohols. Our results reveal that typical long-chain alcohols contribute SOA formation via esterification rather than oligomerization because OSA/OSI produced by esterification engages in nanoparticle growth through enhancing hygroscopicity. Graphical Abstract [Display omitted] [ABSTRACT FROM AUTHOR]

Secondary organic aerosol (SOA) produced by ozonolysis of styrene and other alkene compounds is a major part of fine particles in urban atmospheres. The atmospheric ozonolysis process of styrene is simulated in a smog chamber, and the formed SOA particles are detected on‐line by a synchronous radiation vacuum ultraviolet photoionization mass spectrometer (VUV‐PIMS) in this study. Through molecular ion peaks in the photonionization mass spectra of SOA and the corresponding photoionization efficiency curve, combined with off‐line measurement verification of ultraviolet visible and infrared absorption spectra, it is determined that formaldehyde, formic acid, benzene, phenol, benzaldehyde, and benzoic acid are the main constituents of styrene SOA. These provide new information for studying the atmospheric ozonolysis oxidation mechanism of styrene. VUV‐PIMS can get over complicated sample preparation procedures, secondary pollution, and other shortcomings of the off‐line method and is a useful instrument to measure constituents and unveil the formation process of SOA particles. [ABSTRACT FROM AUTHOR]

Hydroperoxides are formed in the atmospheric oxidation of volatile organic compounds, in the combustion autoxidation of fuel, in the cold environment of the interstellar medium, and also in some catalytic reactions. They play crucial roles in the formation and aging of secondary organic aerosols and in fuel autoignition. However, the concentration of organic hydroperoxides is seldom measured, and typical estimates have large uncertainties. In this work, we developed a mild and environmental- friendly method for the synthesis of alkyl hydroperoxides (ROOH) with various structures, and we systematically measured the absolute photoionization cross-sections (PICSs) of the ROOHs using synchrotron vacuum ultraviolet-photoionization mass spectrometry (SVUV-PIMS). A chemical titration method was combined with an SVUV-PIMS measurement to obtain the PICS of 4-hydroperoxy-2-pentanone, a typical molecule for combustion and atmospheric autoxidation ketohydroperoxides (KHPs). We found that organic hydroperoxide cations are largely dissociated by loss of OOH. This fingerprint was used for the identification and accurate quantification of the organic peroxides, and it can therefore be used to improve models for autoxidation chemistry. The synthesis method and photoionization dataset for organic hydroperoxides are useful for studying the chemistry of hydroperoxides and the reaction kinetics of the hydroperoxy radicals and for developing and evaluating kinetic models for the atmospheric autoxidation and combustion autoxidation of the organic compounds. [ABSTRACT FROM AUTHOR]

Nitroguaiacols are typical constituents of biomass-burning emissions, including absorbing aerosols which contribute to climate change. Although they are also harmful to humans and plants, their atmospheric fate and lifetimes are still very speculative. Therefore, in this work, the photolysis kinetics of aqueous-phase 4-nitroguaiacol (4NG) and 5-nitroguaiacol (5NG), and the resulting photo-formed products were investigated under artificial sunlight, observing also the effect of sunlight on the absorption properties of the solutions. We found the photolysis of 5NG slower than that of 4NG, whereas the absorbance in the visible range prevailed in the 5NG solutions at the end of experiments. Although we identified dinitroguaiacol as one of the 4NG photolysis products, which increased light absorption of 4NG-containing solutions, considerably more chromophores formed in the 5NG photolyzed solutions, implying its stronger potential for secondary BrC formation in the atmosphere. In general, denitration, carbon loss, hydroxylation, nitration, and carbon gain were characteristic of 4NG phototransformation, while carbon loss, hydroxylation, and carbon gain were observed in the case of 5NG. The photolysis kinetics was found of the first order at low precursor concentrations (

In this study, we reviewed smog chamber systems and methodologies used in secondary organic aerosol (SOA) formation studies. Many important chambers across the world have been reviewed, including 18 American, 24 European, and 8 Asian chambers. The characteristics of the chambers (location, reactor size, wall materials, and light sources), measurement systems (popular equipment and working principles), and methodologies (SOA yield calculation and wall-loss correction) are summarized. This review discussed key experimental parameters such as surface-to-volume ratio (S/V), temperature, relative humidity, light intensity, and wall effect that influence the results of the experiment, and how the methodologies have evolved for more accurate simulation of atmospheric processes. In addition, this review identifies the sources of uncertainties in finding SOA yields that are originated from experimental systems and methodologies used in previous studies. The intensity of the installed artificial lights (photolysis rate of NO2 varied from 0.1/min to 0.40/min), SOA density assumption (varied from 1 g/cm3 to 1.45 g/cm3), wall-loss management, and background contaminants were identified as important sources of uncertainty. The methodologies developed in previous studies to minimize those uncertainties are also discussed.

One barrier to predicting biogenic secondary organic aerosol (SOA) formation in a changing climate can be attributed to the complex nature of plant volatile emissions. Plant volatile emissions are dynamic over space and time, and change in response to environmental stressors. This study investigated SOA production from emissions of healthy and aphid-stressed Scots pine saplings via dark ozonolysis and photooxidation chemistry. Laboratory experiments using a batch reaction chamber were used to investigate SOA production from different plant volatile mixtures. The volatile mixture from healthy plants included monoterpenes, aromatics, and a small amount of sesquiterpenes. The biggest change in the volatile mixture for aphid-stressed plants was a large increase (from 1.4 to 7.9 ppb) in sesquiterpenes-particularly acyclic sesquiterpenes, such as the farnesene isomers. Acyclic sesquiterpenes had different effects on SOA production depending on the chemical mechanism. Farnesenes suppressed SOA formation from ozonolysis with a 9.7-14.6% SOA mass yield from healthy plant emissions and a 6.9-10.4% SOA mass yield from aphid-stressed plant emissions. Ozonolysis of volatile mixtures containing more farnesenes promoted fragmentation reactions, which produced higher volatility oxidation products. In contrast, plant volatile mixtures containing more farnesenes did not appreciably change SOA production from photooxidation. SOA mass yields ranged from 10.8 to 23.2% from healthy plant emissions and 17.8-26.8% for aphid-stressed plant emissions. This study highlights the potential importance of acyclic terpene chemistry in a future climate regime with an increased presence of plant stress volatiles.

Anthropogenic nitrogen oxides may influence the cloud condensation nuclei (CCN) activity of biogenic secondary organic aerosols (SOA) in both daytime photooxidation and nighttime NO3 oxidation, which has significant implications for the climatic impact of SOA. We investigated the influence of NOx on the CCN activity of monoterpene‐derived SOA in OH oxidation and in NO3 oxidation. In OH oxidation, NOx had little influence on the hygroscopic parameter κ of organic aerosol (κOrg), which was attributed to the minor fraction of organic nitrates (ON) in SOA (<24%), resulted from the low branching ratio of RO2 + NO to form ON. In contrast, in NO3 oxidation κOrg was much reduced compared to OH/O3 oxidation due to a dominant fraction of ON. We report κ of MT‐derived ON formed in photo‐oxidation and NO3 oxidation (0.029–0.052) for the first time to our knowledge, which may be used to improve model simulations of CCN concentrations. Plain Language Summary: Anthropogenic nitrogen oxides may influence the cloud formation ability of biogenic secondary organic aerosols (SOA) in both daytime and nighttime, which has implications to understand the climatic impact of SOA. However, the influence remains unclear. We found that for monoterpenes, a major class of precursors of biogenic SOA, NOx had little influence on the cloud formation ability of SOA in the daytime oxidation. In contrast, in the nighttime oxidation of monoterpenes by NO3, an important oxidant formed from NOx at night‐time, SOA had much lower cloud formation ability than that in the photo‐oxidation. The difference was attributed to the different fractions of organic nitrates (ON) in SOA. We also determined the κ of monoterpene‐derived ON for the first time to our knowledge. Key Points: In daytime OH oxidation NOx had little influences on the cloud condensation nuclei (CCN) activity of MT‐SOAIn nighttime NO3 oxidation MT‐SOA had much lower CCN activity compared with those formed via OH or O3 oxidationWe report the κ of monoterpene‐derived organic nitrates (0.029–0.052) for the first time to our knowledge [ABSTRACT FROM AUTHOR]

This study divided a basin metropolitan area with high air pollution into three subareas, namely urban, suburban, and rural, on the basis of population density for a systematic analysis of the effects of local air pollutants on respiratory diseases. A panel data regression model was used to estimate the annual incidence growth rates (AIGRs) of the four respiratory diseases, namely lung cancer, chronic obstructive pulmonary disease, asthma, and pneumonia, resulting from exposure to fine particulate matter (PM2.5, diameter of 2.5 μm or less), odd oxygen (ODO), or nonmethane hydrocarbon (NMHC). The results indicate that the prevailing wind direction is not a major factor determining the distribution of air pollutants. The spatial distributions of ODO and NMHC differed from that of PM2.5. Three air pollutants contributed to positive AIGRs of the four diseases in the study area, but PM2.5 which had a negative AIGR for asthma in the rural subarea. The pollutants with the strongest effects on AIGR, in descending order, were NMHC, PM2.5, and ODO. The effect of ambient NMHC was significant and nonnegligible, especially in the urban subarea. A dimensionless potential AIGR (PAIGR) formula was established to quantitatively compare the effects of different air pollutants on the four respiratory diseases. The results indicate that ambient NMHC had the strongest effect on the incidences of the respiratory diseases, followed by that of ambient PM2.5. The effect of ambient NMHC was significant and nonnegligible, especially in the urban subarea. The PAIGR ratio ranges of PM2.5 to ODO and NMHC to ODO for the four diseases in urban subsarea were from 3 to 19 and from 289 to 920, respectively. This study also applied multivariate regression to assess the association among 5 aspects, namely air quality, point source, line source, area source, and socioeconomic status, and the incidences of the four respiratory diseases. The results indicate that the model has favorable fit and can thus reflect the associations of the 15 factors of 5 aspects with the four respiratory diseases in each subarea. [ABSTRACT FROM AUTHOR]

• The complex dynamics physical and chemical processes and the corresponding influencing factors involved in SOA formation and aging mainly based on the results of photochemical smog chamber simulation studies were reviewed. • The properties of the precursor VOCs, the oxidates (such as OH radicals), and the atmospheric environment (such as NO X , SO 2 , NH 3 , light intensity, temperature, humidity and seed aerosols) work together to influence the products and yield of SOA. ► Nucleation and vapor pressure of the products were found to be the most fundamental reasons for interpreting dynamics of SOA formation and aging process. • The prospects for the study direction of the SOA formation and aging are predicted. The formation and aging mechanism of secondary organic aerosol (SOA) and its influencing factors have attracted increasing attention in recent years because of their effects on climate change, atmospheric quality and human health. However, there are still large errors between air quality model simulation results and field observations. The currently undetected components during the formation and aging of SOA due to the limitation of current monitoring techniques and the interactions among multiple SOA formation influencing factors might be the main reasons for the differences. In this paper, we present a detailed review of the complex dynamic physical and chemical processes and the corresponding influencing factors involved in SOA formation and aging. And all these results were mainly based the studies of photochemical smog chamber simulation. Although the properties of precursor volatile organic compounds (VOCs), oxidants (such as OH radicals), and atmospheric environmental factors (such as NO x , SO 2 , NH 3 , light intensity, temperature, humidity and seed aerosols) jointly influence the products and yield of SOA, the nucleation and vapor pressure of these products were found to be the most fundamental aspects when interpreting the dynamics of the SOA formation and aging process. The development of techniques for measuring intermediate species in SOA generation processes and the study of SOA generation and aging mechanism in complex systems should be important topics of future SOA research. [Display omitted] [ABSTRACT FROM AUTHOR]

The impact of relative humidity (RH) on organic new particle formation (NPF) from ozonolysis of monoterpenes remains an area of active debate. Previous reports provide contradictory results indicating both depression and enhancement of NPF under conditions of moderate RH, while others do not indicate a potential impact. Only several reports have suggested that the effect may depend on absolute mixing ratio of the precursor volatile organic compound (VOC, ppbv). Herein we report on the impact of RH on NPF from dark ozonolysis of α- and β-pinene at mixing ratios ranging from 0.2 to 80 ppbv. We show that RH enhances NPF (by a factor of eight) at the lowest α-pinene mixing ratio, with a very strong dependence on α-pinene mixing ratio from 4 to 22 ppbv. At higher mixing ratios, the effect of RH plateaus, with resulting modest decreases in NPF. In the case of α- and β-pinene, NPF is enhanced at low mixing ratios due to a combination of chemistry, accelerated kinetics, and reduced partitioning of semi-volatile oxidation products to the particulate phase. Reduced partitioning would limit particle growth, permitting increased gas-phase concentrations of semi- and low-volatility products, which could favor NPF. [ABSTRACT FROM AUTHOR]

Intermediate volatility organic compounds (IVOCs) and semi-volatile organic compounds (SVOCs) have recently been proposed as important precursors of secondary organic aerosol (SOA). In the present work, 97 volatile organic compounds (VOCs) and 80 intermediate volatility and semi-volatile organic compounds (IVOCs and SVOCs) were measured by online gas chromatography-mass spectrometer/flame ionization detection (GC-MS/FID), and offline thermal desorption gas chromatography-mass spectrometer (TD-GC-MS), respectively. The average concentration of speciated VOCs, IVOCs, and SVOCs were 22.36 ± 9.02 μg m−3, 1.01 ± 0.32 μg m−3, and 0.10 ± 0.17 μg m−3. Alkanes and polycyclic aromatic hydrocarbons (PAHs) are the main compounds of total S/IVOCs. With the increase in molecular weight, the concentrations decreased in the gas phase, while increasing in the particle phase. Vehicular emission is the most significant source according to the carbon preference index (CPI) and the carbon of the most abundant alkane (Cmax). The yield method was used to estimate SOA from the oxidation of VOCs and S/IVOCs. The estimated SOA mass from IVOCs and SVOCs (0.70 ± 0.57 μg m−3) was comparable to that of VOCs (0.62 ± 0.61 μg m−3), and the oxidation of PAHs and alkanes took up 28.70 ± 8.26% and 51.97 ± 20.77% of the total SOA estimation, respectively. Compared to previous work, our study provided detailed molecular information of ambient S/IVOC species and elucidated their importance on SOA formation. Despite their low concentration, S/IVOCs species are important SOA precursors which shared comparable contribution compared with VOCs. [ABSTRACT FROM AUTHOR]

Understanding the effects of mixed anthropogenic pollutants on the photooxidation of volatile organic compounds (VOCs) is essential for unraveling the formation pathways of secondary organic aerosols (SOA). Yet, it remains a highly challenging experimental target owing to the complexities in the precise measurement of molecular compositions of products and number/mass concentrations of particles as a function of pollutant concentration in the ambient atmosphere. Here, a series of well-defined chamber experiments were performed to explore the effects of NO x and NH 3 on the SOA formation from photooxidation of the most abundant monoterpene, α -pinene. The results indicate that the suppression effect of NO and NO 2 on the α -pinene photooxidation shows monotonous and parabolic trends, respectively. The presence of NH 3 enhances particle number concentrations during the α -pinene + NO x photooxidation by participating in reactions with organic acids. New compounds, including organic peroxides, esters, organic nitrates, and peroxyacyl nitrates, are observed at molecular weight (MW) = 166, 173, 217, 231, 280, 282, 304, and 410 through threshold photoionization making use of a recently constructed vacuum ultraviolet free electron laser in positive ion mode. The molecular structures and formation paths of these species are speculated, which advance the category of VOC oxidation products. Our study provides significant understanding of the influence of NO x and NH 3 on the VOC photooxidation, which can be utilized to establish predictive SOA formation networks and to improve atmospheric models. [Display omitted] • This study investigates the atmospheric components affected by the anthropogenic-biogenic interactions. • The suppression effect of NO and NO 2 on the α -pinene photooxidation shows monotonous and parabolic trends, respectively. • NH 3 enhances the number concentrations of SOA from the α -pinene + NO x photooxidation by reacting with organic acids. • A series of newly-observed compounds advance understanding of atmospheric components. [ABSTRACT FROM AUTHOR]