Smog Chamber Research Articles

Secondary organic aerosol formation from mixed volatile organic compounds: Effect of RO2 chemistry and precursor concentration

Secondary organic aerosol (SOA) plays a significant role in contributing to atmospheric fine particles, as well as in global air quality and climate. However, the current understanding of the atmospheric formation of SOA and its simulation is still highly uncertain due to the complexity of its precursor VOCs. In our study, SOA formation in different mixed VOC scenarios was investigated using a 30 m3 indoor smog chamber. By comparing SOA formation in individual VOC scenarios, it was found that SOA yield from anthropogenic VOCs (AVOCs) can be positively (+83.9%) affected by coexisting AVOCs, while inhibited (−51.4%) by the presence of isoprene, via the OH scavenging effect. The cross-reactions of peroxyl radical (RO2) generated from different AVOCs were proved to be the main contributor (up to 39.0%) to SOA formation, highlighting the importance of RO2 + RʹO2 reactions in mixed VOC scenarios. Meanwhile, the formation of gas-phase organic intermediates of different volatility categories from the RO2 reactions was also affected by the precursor concentration, and a higher SOA yield was found at lower precursor concentrations due to the larger contribution of intermediates with lower volatility. Our study provides new insights into SOA formation by considering the interactions between intermediate products from mixed VOCs.

Smog chamber study of secondary organic aerosol formation from gas- and particle-phase naphthalene ozonolysis

Naphthalene (Nap), one of the most abundant PAHs in the atmosphere, has been shown to be an important secondary organic aerosol (SOA) precursor. In this study, the gas- and particle-phases (Suspended Nap-coated polystyrene latex spheres (PSLs) generated by vaporization condensation) Nap ozonolysis were investigated in a 1000 L volume cubic Teflon smog chamber. Gas-phase products and Nap-SOAs were observed from the gas- and particle-phase Nap ozonolysis via homogeneous and heterogeneous reactions, respectively. The time-dependent size distribution and mass concentration of Nap-SOAs were analyzed using a scanning mobility particle sizer and a laboratory-developed single-particle aerosol mass spectrometry (SPAMS) instrument. The chemical components of the homogeneous and heterogeneous reaction products were analyzed on-line by single photo ionization mass spectrometry (SPIMS), SPAMS, as well as by thermal desorption gas chromatograph-mass spectrometry. The results showed that the chemical components of the gas-and particle-phase Nap ozonolysis were essentially the same, with the dominant products being phthalaldehyde, phthalic anhydride, 2-carboxybenzaldehyde, and benzoic acid; Nap-SOA formation was attributed to the formation of new particles as well as the uptake of homogeneous and heterogeneous Nap oxidation products on the gas-phase or/and the particle surface. Based on the online measurement results, the reaction mechanism of Nap-ozonolysis also exhibits an initial carbon atom or double-bond attacks by O3, and kinetic analysis of Nap-coated PSLs ozonolysis shows a heterogeneous reaction rate constant of 2.55E-4 s−1 with R2 = 0.984. This study provides a systematic approach to characterize the chemical and physical properties of the gas- and particle-phase Nap ozonolysis in real time, which will deepen our understanding of the migration and transformation of PAHs in the atmosphere.

Review of the influencing factors of secondary organic aerosol formation and aging mechanism based on photochemical smog chamber simulation methods

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 NOx, SO2, NH3, 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.

A lumped species approach for the simulation of secondary organic aerosol production from intermediate-volatility organic compounds (IVOCs): application to road transport in PMCAMx-iv (v1.0)

Abstract. Secondary organic aerosol (SOA) is formed in the atmosphere through the oxidation and condensation of organic compounds. Intermediate-volatility compounds (IVOCs), compounds with effective saturation concentration (C∗) at 298 K between 103 and 106 µg m−3, have high SOA yields and can be important SOA precursors. The first efforts to simulate IVOCs in chemical transport models (CTMs) used the volatility basis set (VBS), a highly parametrized scheme that oversimplifies their chemistry. In this work we propose a more detailed approach for simulating IVOCs in CTMs, treating them as lumped species that retain their chemical characteristics. Specifically, we introduce four new lumped species representing large alkanes, two lumped species representing polyaromatic hydrocarbons (PAHs) and one species representing large aromatics, all in the IVOC range. We estimate IVOC emissions from road transport using existing estimates of volatile organic compound (VOC) emissions and emission factors of individual IVOCs from experimental studies. Over the European domain, for the simulated period of May 2008, estimated IVOC emissions from road transport were about 21 Mmol d−1, a factor of 8 higher than emissions used in previous VBS applications. The IVOC emissions from diesel vehicles were significantly higher than those from gasoline ones. SOA yields under low-NOx and high-NOx conditions for the lumped IVOC species were estimated based on recent smog chamber studies. Large cyclic alkane compounds have both high yields and high emissions, making them an important, yet understudied, class of IVOCs.

Smog Chamber Study on the Role of NOxin SOA and O3Formation from Aromatic Hydrocarbons

China is facing dual pressures to reduce both PM2.5 and O3 pollution, the crucial precursors of which are NOx and VOCs. In our study, the role of NOx in both secondary organic aerosol (SOA, the important constituent of PM2.5) and O3 formation was examined in our 30 m3 indoor smog chamber. As revealed in the present study, the NOx level can obviously affect the OH concentration and volatility distribution of gas-phase oxidation products and thus O3 and SOA formation. Reducing the NOx concentration to the NOx-sensitive regime can inhibit O3 formation (by 42%), resulting in the reduction of oxidation capacity, which suppresses the SOA formation (by 45%) by inhibiting the formation of O- and N-containing gas-phase oxidation products with low volatility. The contribution of these oxidation products to the formation of SOA was also estimated, and the results could substantially support the trend of SOA yield with NOx at different VOC levels. The atmospheric implications of NOx in the coordinated control of PM2.5 and O3 are also discussed.

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.

A vehicle-mounted dual-smog chamber: Characterization and its preliminary application to evolutionary simulation of photochemical processes in a quasi-realistic atmosphere

Smog chambers are the effective tools for studying formation mechanisms of air pollution. Simulations by traditional smog chambers differ to a large extent from real atmospheric conditions, including light, temperature and atmospheric composition. However, the existing parameters for mechanism interpretation are derived from the traditional smog chambers. To address the gap between the traditional laboratory simulations and the photochemistry in the real atmosphere, a vehicle-mounted indoor-outdoor dual-smog chamber (JNU-VMDSC) was developed, which can be quickly transferred to the desired sites to simulate quasi-realistic atmosphere simultaneously in both chambers using “local air”. Multiple key parameters of the smog chamber were characterized in the study, demonstrating that JNU-VMDSC meets the requirements of general atmospheric chemistry simulation studies. Additionally, the preliminary results for the photochemical simulations of quasi-realistic atmospheres in Pearl River Delta region and Nanling Mountains are consistent with literature reports on the photochemistry in this region. JNU-VMDSC provides a convenient and reliable experimental device and means to study the mechanism of atmospheric photochemical reactions to obtain near-real results, and will make a great contribution to the control of composite air pollution.

Combined application of online FIGAERO-CIMS and offline LC-Orbitrap mass spectrometry (MS) to characterize the chemical composition of secondary organic aerosol (SOA) in smog chamber studies

Abstract. A combination of online and offline mass spectrometric techniques was used to characterize the chemical composition of secondary organic aerosol (SOA) generated from the photooxidation of α-pinene in an atmospheric simulation chamber. The filter inlet for gases and aerosols (FIGAERO) coupled with a high-resolution time-of-flight iodide chemical ionization mass spectrometer (I−-ToF-CIMS) was employed to track the evolution of gaseous and particulate components. Extracts of aerosol particles sampled onto a filter at the end of each experiment were analysed using ultra-performance liquid chromatography ultra-high-resolution tandem mass spectrometry (LC-Orbitrap MS). Each technique was used to investigate the major SOA elemental group contributions in each system. The online CIMS particle-phase measurements show that organic species containing exclusively carbon, hydrogen, and oxygen (CHO group) dominate the contribution to the ion signals from the SOA products, broadly consistent with the LC-Orbitrap MS negative mode analysis, which was better able to identify the sulfur-containing fraction. An increased abundance of high-carbon-number (nC≥16) compounds additionally containing nitrogen (CHON group) was detected in the LC-Orbitrap MS positive ionization mode, indicating a fraction missed by the negative-mode and CIMS measurements. Time series of gas-phase and particle-phase oxidation products provided by online measurements allowed investigation of the gas-phase chemistry of those products by hierarchical clustering analysis to assess the phase partitioning of individual molecular compositions. The particle-phase clustering was used to inform the selection of components for targeted structural analysis of the offline samples. Saturation concentrations derived from nearly simultaneous gaseous and particulate measurements of the same ions by FIGAERO-CIMS were compared with those estimated from the molecular structure based on the LC-Orbitrap MS measurements to interpret the component partitioning behaviour. This paper explores the insight brought to the interpretation of SOA chemical composition by the combined application of online FIGAERO-CIMS and offline LC-Orbitrap MS analytical techniques.

Compilation of reaction kinetics parameters determined in the Key Development Project for Air Pollution Formation Mechanism and Control Technologies in China

A compilation of new advances made in the research field of laboratory reaction kinetics in China's Key Development Project for Air Pollution Formation Mechanism and Control Technologies was presented. These advances are grouped into six broad, interrelated categories, including volatile organic compound (VOC) oxidation, secondary organic aerosol (SOA) formation, new particle formation (NPF) and gas-particle partitioning, ozone chemistry, model parameters, and secondary inorganic aerosol (SIA) formation, highlighting the laboratory work done by Chinese researchers. For smog chamber applications, the current knowledge gained from laboratory studies is reviewed, with emphasis on summarizing the oxidation mechanisms of long-chain alkanes, aromatics, alkenes, aldehydes/ketones in the atmosphere, SOA formation from anthropogenic emission sources, and oxidation of aromatics, isoprene, and limonene, as well as SIA formation. For flow tube applications, atmospheric oxidation mechanisms of toluene and methacrolein, SOA formation from limonene oxidation by ozone, gas-particle partitioning of peroxides, and sulfuric acid-water (H2SO4-H2O) binary nucleation, methanesulfonic acid-water (MSA-H2O) binary nucleation, and sulfuric acid-ammonia-water (H2SO4-NH3-H2O) ternary nucleation are discussed.

Direct measurements of ozone response to emissions perturbations in California

Abstract. A new technique was used to directly measure O3 response to changes in precursor NOx and volatile organic compound (VOC) concentrations in the atmosphere using three identical Teflon smog chambers equipped with UV lights. One chamber served as the baseline measurement for O3 formation, one chamber added NOx, and one chamber added surrogate VOCs (ethylene, m-xylene, n-hexane). Comparing the O3 formation between chambers over a 3-hour UV cycle provides a direct measurement of O3 sensitivity to precursor concentrations. Measurements made with this system at Sacramento, California, between April–December 2020 revealed that the atmospheric chemical regime followed a seasonal cycle. O3 formation was VOC-limited (NOx-rich) during the early spring, transitioned to NOx-limited during the summer due to increased concentrations of ambient VOCs with high O3 formation potential, and then returned to VOC-limited (NOx-rich) during the fall season as the concentrations of ambient VOCs decreased and NOx increased. This seasonal pattern of O3 sensitivity is consistent with the cycle of biogenic emissions in California. The direct chamber O3 sensitivity measurements matched semi-direct measurements of HCHO/NO2 ratios from the TROPOspheric Monitoring Instrument (TROPOMI) aboard the Sentinel-5 Precursor (Sentinel-5P) satellite. Furthermore, the satellite observations showed that the same seasonal cycle in O3 sensitivity occurred over most of the entire state of California, with only the urban cores of the very large cities remaining VOC-limited across all seasons. The O3-nonattainment days (MDA8 O3>70 ppb) have O3 sensitivity in the NOx-limited regime, suggesting that a NOx emissions control strategy would be most effective at reducing these peak O3 concentrations. In contrast, a large portion of the days with MDA8 O3 concentrations below 55 ppb were in the VOC-limited regime, suggesting that an emissions control strategy focusing on NOx reduction would increase O3 concentrations. This challenging situation suggests that emissions control programs that focus on NOx reductions will immediately lower peak O3 concentrations but slightly increase intermediate O3 concentrations until NOx levels fall far enough to re-enter the NOx-limited regime. The spatial pattern of increasing and decreasing O3 concentrations in response to a NOx emissions control strategy should be carefully mapped in order to fully understand the public health implications.

Secondary organic aerosol formation from cis-3-hexen-1-ol/NOx photo-oxidation: The roles of cis-3-hexen-1-ol concentration, illumination intensity, NOx and NH3

Cis-3-Hexen-1-ol (cis-HXO) is an important green leaf volatile (GLV), and its photochemical oxidation is an important pathway to generate secondary organic aerosol (SOA). In this study, smog chamber experiments were carried out to investigate the effects of cis-HXO concentration, illumination intensity, and nitrogen oxides (NOX) and ammonia (NH3) levels on the formation of cis-HXO photo-oxidation SOA in the presence of NOX. The number concentration, mass concentration and yield of SOA under different influencing factors were determined using a scanning mobility particle sizer (SMPS) and a single photon ionization time-of-flight mass spectrometer (SPIMS). The experimental results demonstrated that stronger illumination intensity and higher cis-HXO concentration promoted particles formation. The SOA yield showed a good positive correlation with NOX concentration, especially under high NOX conditions, due to the fragmentation of alkoxy radicals during the reaction to form more polymerizable products as well as the presence of dinitrate and trinitrate, thus promoting the production of SOA. To our surprise, although the addition of NH3 promoted the formation of particles, it inhibited the growth of particles, and thus reducing the particles geometric mean diameter. The chemical components of cis-HXO photo-oxidation SOAs were also analyzed by a thermal-desorption gas chromatography mass spectrometry (TD-GC-MS). Based on the detected products, a reaction mechanism for the cis-HXO photo-oxidation was proposed. The experimental results confirm that cis-HXO is a significant global source of SOA which has a great reference significance for regional air quality prediction and more accurate modelling of global SOA generation.

Secondary organic aerosol formation from photooxidation of γ-butyro and γ-valero-lactone: A combined experimental and theoretical study

The formation of secondary organic aerosol (SOA) generated by OH-photooxidation of γ-butyrolactone (GBL) and γ-valerolactone (GVL) in the presence of OH, NO, H2O vapour and aerosol seeds ((NH4)2SO4 and CaCl2) has been investigated for the first time. Experiments were conducted in a smog chamber at 298 K and atmospheric pressure. Lactone's decay was followed by gas chromatography with a mass spectrometric detector (GC-MS), and the temporal evolution of the SOA was monitored using a fast mobility particle sizer (FMPS). The SOA yield increases slightly when the initial GVL concentration increases. On the other hand, SOA formation is minor for GBL, and it rises slightly at low concentrations. In the case of GVL, the organic aerosol formation can be tentatively expressed by a one-product gas/particle partitioning absorption model. The particle number concentration, mass and yield decrease in the presence of NO but increase at higher relative humidity (RH) and seed surface area within the studied range. Acetic acid and succinic anhydride for GVL, and succinic anhydride for GBL were experimentally identified as oxidation products both in gas and particle phase using thermal desorption followed by GC-MS. Moreover, the theoretical studies carried out to complement the experimental results indicate that H-abstraction at the carbon site adjacent to the heterocyclic oxygen is the predominant pathway, being even more favourable when H2O was added. Also, under atmospheric conditions, the opening of the ring of the corresponding oxy-radicals and their subsequent fragmentation could be the possible explanation for the formation of detected products and the higher yield of SOA in the presence of H2O and absence of NO. Considering these results, the formation of SOA from the use of both lactones as potential biofuels is few significative, although SOA generation may be enhancement by particle-phase heterogeneous reactions catalyzed by humidity and the acidity of seed aerosols present in real atmosphere.

Evaluation of the daytime tropospheric loss of 2-methylbutanal

Abstract. Saturated aldehydes, e.g. 2-methylbutanal (2 MB, CH3CH2CH(CH3)C(O)H), are emitted into the atmosphere by several biogenic sources. The first step in the daytime atmospheric degradation of 2 MB involves gas-phase reactions initiated by hydroxyl (OH) radicals, chlorine (Cl) atoms, and/or sunlight. In this work, we report the rate coefficients for the gas-phase reaction of 2 MB with OH (kOH) and Cl (kCl), together with the photolysis rate coefficient (J), in the ultraviolet solar actinic region in Valencia (Spain) at different times of the day. The temperature dependence of kOH was described in the 263–353 K range by the following Arrhenius expression: kOH(T)=(8.88±0.41)×10-12 exp[(331±14)/T] cm3 molec.−1 s−1. At 298 K, the reported kOH and kCl are (2.68±0.07)×10-11 and (2.16±0.32)×10-10 cm3 molec.−1 s−1, respectively. Identification and quantification of the gaseous products of the Cl reaction and those from the photodissociation of 2 MB were carried out in a smog chamber by different techniques (Fourier transform infrared spectroscopy, proton transfer time-of-flight mass spectrometry, and gas chromatography coupled to mass spectrometry). The formation and size distribution of secondary organic aerosols formed in the Cl reaction were monitored by a fast mobility particle sizer spectrometer. A discussion on the relative importance of the first step in the daytime atmospheric degradation of 2 MB is presented together with the impact of the degradation products in marine atmospheres.

Cytotoxicity and oxidative stress induced by atmospheric mono-nitrophenols in human lung cells

Nitrophenols (NPs) are hazardous pollutants found in various environmental matrices, including ambient fine particulate matter (PM2.5), agricultural residues, rainwater, wildfires, and industrial wastes. This study showed for the first time the effect of three pure nitrophenols and their mixture on human lung cells to provide basic understanding of the NP influence on cell elements and processes. We identified NPs in ambient PM2.5 and secondary organic aerosol (SOA) particles generated from the photooxidation of monocyclic aromatic hydrocarbons in the U.S. EPA smog chamber. We assessed the toxicity of identified NPs and their equimolar mixture in normal bronchial epithelial (BEAS-2B) and alveolar epithelial cancer (A549) lung cell lines. The inhibitory concentration-50 (IC50) values were highest and lowest in BEAS-2B cells treated with 2-nitrophenol (2NP) and 4-nitrophenol (4NP), respectively, at 24 h of exposure. The lactate dehydrogenase (LDH) assay showed that 4NP, the most abundant NP we identified in PM2.5, was the most cytotoxic NP examined in both cell lines. The annexin-V/fluorescein isothiocyanate (FITC) analysis showed that the populations of late apoptotic/necrotic BEAS-2B and A549 cells exposed to 3NP, 4NP, and NP equimolar mixture increased between 24 and 48 h. Cellular reactive oxygen species (ROS) buildup led to cellular death post exposure to 3NP, 4NP and the NP mixtures, while 2NP induced the lowest ROS buildup. An increased mitochondrial ROS signal following NP exposure occurred only in BEAS-2B cells. The tetramethylrhodamine, methyl ester, perchlorate (TMRM) assay showed that exposed cells exhibited collapse of the mitochondrial membrane potential. TMRM signals decreased significantly only in BEAS-2B cells, and most strongly with 4NP exposures. Our results suggest that acute atmospheric exposures to NPs may be toxic at high concentrations, but not at ambient PM2.5 concentrations. Further chronic studies with NP and NP-containing PM2.5 are warranted to assess their contribution to lung pathologies.

Smog chamber simulation on heterogeneous reaction of O3 and NO2 on black carbon under various relative humidity conditions

In this study, heterogeneous formation of nitrate from O3 reaction with NO2 on black carbon (BC) and KCl-treated BC surface in the presence of NH3 was simulated under 30–90% RH conditions by using a laboratory smog chamber. We found that O3 and NO2 in the chamber quickly reacted into N2O5 in the gas phase, which subsequently hydrolyzed into HNO3 and further neutralized with NH3 into NH4NO3 on the BC surface, along with a small amount of N2O5 decomposed into NO and NO2 through a reaction with the BC surface active site. Meanwhile, the fractal BC aggregates restructured and condensed to spherical particles during the NH4NO3 coating process. Compared to that during the exposure to NO2 or O3 alone, the presence of strong signals of CH2O+, CH2O2+ and CH4NO+ during the simultaneous exposure to both NO2 and O3 suggested a synergetic oxidizing effect of NO2 and O3, which significantly activated the BC surface by forming carbonyl, carboxylic and nitro groups, promoted the adsorption of water vapor onto the BC surface and enhanced the NH4NO3 formation. Under <75 ± 2% RH conditions the coating process of NH4NO3 on the BC surface consisted of a diffusion of N2O5 onto the surface and a subsequent hydrolysis, due to the limited number of water molecules adsorbed. However, under 90 ± 2% RH conditions N2O5 directly hydrolyzed on the aqueous phase of the BC surface due to the multilayer water molecules adsorbed, which caused an instant NH4NO3 formation on the surface without any delay. The coating rate of NH4NO3 on KCl-treated BC particles was 3–4 times faster than that on the pure BC particles at the initial stage, indicating an increasing formation of NH4NO3, mainly due to an enhanced hygroscopicity of BC by KCl salts.

Comparing black-carbon- and aerosol-absorption-measuring instruments – a new system using lab-generated soot coated with controlled amounts of secondary organic matter

Abstract. We report on an inter-comparison of black-carbon- and aerosol-absorption-measuring instruments with laboratory-generated soot particles coated with controlled amounts of secondary organic matter (SOM). The aerosol generation setup consisted of a miniCAST 5201 Type BC burner for the generation of soot particles and a new automated oxidation flow reactor based on the micro smog chamber (MSC) for the generation of SOM from the ozonolysis of α-pinene. A series of test aerosols was generated with elemental to total carbon (EC / TC) mass fraction ranging from about 90 % down to 10 % and single-scattering albedo (SSA at 637 nm) from almost 0 to about 0.7. A dual-spot Aethalometer AE33, a photoacoustic extinctiometer (PAX, 870 nm), a multi-angle absorption photometer (MAAP), a prototype photoacoustic instrument, and two prototype photo-thermal interferometers (PTAAM-2λ and MSPTI) were exposed to the test aerosols in parallel. Significant deviations in the response of the instruments were observed depending on the amount of secondary organic coating. We believe that the setup and methodology described in this study can easily be standardised and provide a straightforward and reproducible procedure for the inter-comparison and characterisation of both filter-based and in situ black-carbon-measuring (BC-measuring) instruments based on realistic test aerosols.

A New Type of Quartz Smog Chamber: Design and Characterization.

Since the 1960s, many indoor and outdoor smog chambers have been developed worldwide. However, most of them are made of Teflon films, which have relatively high background contaminations due to the wall effect. We developed the world's first medium-size quartz chamber (10 m3), which is jointed with 32 pieces of 5 mm thick polished quartz glasses and a stainless-steel frame. Characterizations show that this chamber exhibits excellent performance in terms of relative humidity (RH) (2-80%) and temperature (15-30 ± 1 °C) control, mixing efficiency of the reactants (6-8 min), light transmittance (>90% above 290 nm), and wall loss of pollutants. The wall loss rates of the gas-phase pollutants are on the order of 10-4 min-1 at 298 K under dry conditions. It is 0.08 h-1 for 100-500 nm particles, significantly lower than those of Teflon chambers. The photolysis rate of NO2 (JNO2) is automatically adjustable to simulate the diurnal variation of solar irradiation from 0 to 0.40 min-1. The inner surface of the chamber can be repeatedly washed with deionized water, resulting in low background contaminations. Both experiments (toluene-NOx and α-pinene-ozone systems) and box model demonstrate that this new quartz chamber can provide high-quality data for investigating SOA and O3 formation in the atmosphere.

Assessing the influence of environmental conditions on secondary organic aerosol formation from a typical biomass burning compound

The atmospheric chemistry in complex air pollution remains poorly understood. In order to probe how environmental conditions can impact the secondary organic aerosol (SOA) formation from biomass burning emissions, we investigated the photooxidation of 2,5-dimethylfuran (DMF) under different environmental conditions in a smog chamber. It was found that SO2 could promote the formation of SOA and increase the amounts of inorganic salts produced during the photooxidation. The formation rate of SOA and the corresponding SOA mass concentration increased gradually with the increasing DMF/OH ratio. The addition of (NH4)2SO4 seed aerosol accelerated the SOA formation rate and significantly shortened the time for the reaction to reach equilibrium. Additionally, a relatively high illumination intensity promoted the formation of OH radicals and, correspondingly, enhanced the photooxidation of DMF. However, the enhancement of light intensity accelerated the aging of SOA, which led to a gradual decrease of the SOA mass concentration. This work shows that by having varying influence on atmospheric chemical reactions, the same environmental factor can affect SOA formation in different ways. The present study is helpful for us to better understand atmospheric complex pollution.

Study on the reaction of 3-methyl-2-butenal and 3-methylbutanal with Cl atoms: kinetics and reaction mechanism

The reaction of Cl atoms with two C5 aldehydes (3-methyl-2-butenal and 3-methylbutanal) were investigated by proton-transfer-reaction mass spectrum (PTR-MS) using smog chamber at 298 ± 1 K and 760 Torr. A relative rate method was used to determine the rate constants of the title reactions with m-xylene and trans-2-butene as reference compounds: (3.04 ± 0.18) × 10−10 and (2.07 ± 0.14) × 10−10 cm3/(molecule⋅sec) for 3-methyl-2-butenal and 3-methylbutanal, respectively. Additionally, the gas-phase products were also identified by PTR-MS, and the possible reaction mechanisms were proposed basing on the identified products. The detected gas-phase products are similar for two C5 aldehydes reactions, mainly including small molecules of aldehydes, ketones and chlorinated aldehyde compounds. The atmospheric lifetimes (τ) calculated for 3-methyl-2-butenal (τ = 7.0 hr, marine boundary layer (MBL)) and 3-methylbutanal (τ = 10.3 hr, MBL) according to the obtained rate constants. The results indicate that Cl atoms at MBL are competitive with OH radicals for the degradation contribution of C5 aldehyde compounds.

Aerosol mass spectrometry of neutral species based on a tunable vacuum ultraviolet free electron laser.

A vacuum ultraviolet free electron laser (VUV-FEL) photoionization aerosol mass spectrometer (AMS) has been developed for online measurement of neutral compounds in laboratory environments. The aerosol apparatus is mainly composed of a smog chamber and a reflectron time-of-flight mass spectrometer (TOF-MS). The indoor smog chamber had a 2 m3 fluorinated ethylene propylene film reactor placed in a temperature- and humidity-controlled room, which was used to generate the aerosols. The aerosols were sampled via an inlet system consisting of a 100 μm orifice nozzle and aerodynamic lenses. The application of this VUV-FEL AMS to the α-pinene ozonolysis under different concentrations reveals two new compounds, for which the formation mechanisms are proposed. The present findings contribute to the mechanistic understanding of the α-pinene ozonolysis in the neighborhood of emission origins of α-pinene. The VUV-FEL AMS method has the potential for chemical analysis of neutral aerosol species during the new particle formation processes.