article a smog chamber facility for qualitative and

CHINESE JOURNAL OF CHEMICAL PHYSICS VOLUME 27, NUMBER 6 DECEMBER 27, 2014

ARTICLE

A Smog Chamber Facility for Qualitative and Quantitative Study onAtmospheric Chemistry and Secondary Organic Aerosol

Chang-jin Hua,b, Yue Chengb,c, Gang Panb, Yan-bo Gaia,b, Xue-jun Gua,b, Wei-xiong Zhaoa,b,Zhen-ya Wangb, Wei-jun Zhanga,b,d∗, Jun Chene, Fu-yi Liue, Xiao-bin Shane, Liu-si Shenge

a. Key Laboratory of Atmospheric Composition and Optical Radiation, Anhui Institute of Optics andFine Mechanics, Chinese Academy of Sciences, Hefei 230031, Chinab. Laboratory of Atmospheric Physico-Chemistry, Anhui Institute of Optics and Fine Mechanics, ChineseAcademy of Sciences, Hefei 230031, Chinac. No.8 Research Institute, China Electronics Technology Group Corporation, Hefei 230000, Chinad. School of Environmental Science & Optoelectronic Technology, University of Science and Technologyof China, Hefei 230026, Chinae. National Synchrotron Radiation Laboratory, School of Nuclear Science and Technology, University ofScience and Technology of China, Hefei 230029, China

(Dated: Received on May 29, 2014; Accepted on July 28, 2014)

In order to investigate the atmospheric oxidation processes and the formation of secondaryorganic aerosol (SOA), an indoor environmental reaction smog chamber are constructed andcharacterized. The system consists of the collapsible ∼830 L FEP Teflon film main reactor,in which the atmospheric chemical reactions take place and the formation of SOA occursunder the simulated atmospheric conditions, and the diverse on-line gas- and particle-phaseinstrumentation, such as the proton transfer reaction mass spectrometer, the synchrotronradiation photoionization mass spectrometer, the aerosol laser time-of-flight mass spectrom-eter, and other traditional commercial instruments. The initial characterization experimentsare described, concerning the temperature and ultraviolet light intensity, the reactivity ofthe pure air, the wall loss rates of gaseous compounds and particulate matter. And theinitial evaluation experiments for SOA yields from the ozonolysis of α-pinene and for massspectra of the products resulting from the photooxidation of OH initiated isoprene are alsopresented, which indicate the applicability of this facility on the studies of gas-phase chemicalmechanisms as well as the formation of SOA expected in the atmosphere.

Key words: Smog chamber, Atmospheric chemical reactions, Secondary organic aerosol,Mass spectrum

I. INTRODUCTION

Atmospheric aerosols, consisting of liquid or solidparticles suspended in air, play a key role in many envi-ronmental processes. It is well recognized that organiccompounds make up a substantial fraction of atmo-spheric fine particulate matter and secondary organicaerosol (SOA), resulting from the atmospheric oxida-tion of reactive organic gases, contributes to 45%–60%of the organic aerosol mass in the atmosphere [1, 2]. Asan important source leading to the formation of photo-chemical smog and the increase of ozone concentrationin troposphere [3, 4], SOA is also of climatic interestacting as cloud condensation nuclei [5], and scatter-ing or absorbing solar radiation [6]. Furthermore, asa portion of the organic component of PM2.5 in am-

∗Author to whom correspondence should be addressed. E-mail:[email protected]

bient atmospheres, SOA also has an important impacton human health, and numerous studies have shown aclear linkage between the increased risk of lung canceror cardiovascular disease and the exposure to ambientaerosols [7–9]. However, owing to the complexity of thesource of organic aerosol, the diversity of the chemicalcompounds comprising the SOA faction, and the diffi-culty of isolating chemical and microphysical processesin the atmosphere, our understanding on the formation,properties and impact of SOA is still limited.

Being able to provide controllable and repeatableconditions in which the chemical processes of interestcan be studied separately, environmental reaction smogchamber, especially indoor type, has proven an indis-pensable tool in the study of atmospheric chemistry andSOA formation [10–14]. For example, a state-of-the-art smog chamber facility comprising two 28 m3 Teflonchambers was built for investigation of atmosphericaerosol chemistry at California Institute of Technologyin 2001 [15]. In 2003, Toyota Central Research and De-velopment Laboratories used smog chamber facility to

DOI:10.1063/1674-0068/27/06/631-639 631 c⃝2014 Chinese Physical Society

632 Chin. J. Chem. Phys., Vol. 27, No. 6 Chang-jin Hu et al.

FIG. 1 Schematic of the smog chamber system. 3: Three-way valve, 4: four-way valve, E: electromagnetic valve, MFC:mass flow controller, and HC: hydrocarbon.

study the temperature dependence of SOA formation[16]. In 2005, an indoor environmental reaction smogchamber facility for the study of atmospheric processesleading to the formation of ozone and SOA at very lowreactant concentrations was constructed at Universityof California at Riverside [17]. And almost at the sametime, a temperature-controlled environmental reactionsmog chamber was set up in Paul Scherrer Instituteof Switzerland [18]. Although environmental reactionsmog chamber is essential for developing and evaluat-ing chemical mechanisms or models for predicting theformation of SOA in the absence of uncertainties asso-ciated with emissions, meteorology, and mixing effects,many works in China mainly focused on the kineticsof the atmospheric related oxidation [19–21], and thereis lack of the studies on SOA formation and the corre-sponding atmospheric chemistry and physics based onsmog chamber system in China [22–24]. Especially, theefficient smog chamber facility, which should be com-petent for identifying the chemical composition of gasand particle production of the interesting atmosphericchemical reaction processes and evaluating their contri-bution to the formation of SOA simultaneously, is ap-pealed urgently in China. It is the goal that this workis directed to.

A new indoor environmental reaction smog chamberwas built at Anhui Institute of Optics and Fine Me-chanics, Chinese Academy of Sciences in order to wellinvestigate atmospheric chemical reaction process andmechanism and the formation of SOA. A suite of on-

line instrumentation for the analysis of the gas phaseas well as the aerosol phase, including the proton trans-fer reaction mass spectrometer (PTR-MS), synchrotronradiation photoionization mass spectrometer (SRPIMS)and aerosol laser time-of-flight mass spectrometer (AL-TOFMS), and the corresponding controls are described.Details of the characterization experiments and the evo-lution experiments are also presented, which demon-strate the application of this facility in the studies ofthe oxidation of volatile organic compounds (VOCs) inthe presence (OH initiated oxidation) and absence (O3

initiated oxidation) of UV light.

II. CONSTRUCTION OF THE SMOG CHAMBERFACILITY

The schematic of the smog chamber facility is shownin Fig.1. The facility is roughly divided into three func-tion blocks: a simulation reaction chamber, a compo-nent injection system, and a detection system. The sim-ulation reaction chamber, where the atmospheric chem-ical reaction happens, is a main part made of TeflonFEP material. The component injection system is apart where background gases (purified air, NOx, SO2,or NH3 etc.) or particles (seed aerosol), precursor ofinterested reaction (VOCs) and oxidant (O3 or OH rad-ical) can be injected into the chamber. And the detec-tion system, which is controlled by a PC to meet therequirements of automatic sampling and data record-

DOI:10.1063/1674-0068/27/06/631-639 c⃝2014 Chinese Physical Society

Chin. J. Chem. Phys., Vol. 27, No. 6 Atmospheric Chemistry and Secondary Organic Aerosol 633

TABLE I Components of the pure air system and the corresponding parameters.

Component Type and Producer Parameter description

Air compressor Powerex SLAE05E (USA) Flow rate of 115 L/min

Refrigerating air dryer Drypoint RAC 10-15 (BEKO) Removes the water in the compressed air

T-grade filter Hangzhou Jiamei cleaning equipment Co., Ltd Removes particle above 1 µm and efficiency of

85.7% (10−1000 nm)

A-grade filter Hangzhou Jiamei cleaning equipment Co., Ltd Removes particle above 0.01 µm and efficiency of

94.7% (10−1000 nm)

Balstonr BX filter Model 9922-11 Removes particle above 0.01 µm and efficiency of

99.99% (10−1000 nm)

Pure air generator AADCO 737-15, ADDCO Instruments, 0−250 LPM∗ output flow at 80 psi with less than

Inc. USA 1 ppb O3, SO2, H2S, CS2, and NOx and less than

300 ppb CO2

∗ LPM=liter per minute.

FIG. 2 Schematic of pure air system.

ing, comprises a suite of traditional and non-traditionalinstruments used to monitor gas and particle specieswithin the reactor.

A. Simulation reaction chamber

The main reactor, which is housed inside ahighly reflective aluminum enclosure, is a ∼830 L(1.3 m×0.8 m×0.8 m) flexible bag made of 75 µm FEPTeflon film. FEP Teflon film is one kind of the gener-ally accepted materials in environmental reaction smogchamber designed for its high transparency and chem-ical inertia as being exposed to a near UV irradiation.And collapsible design enables air extraction from thechamber without altering the pressure inside the reac-tor. The low-cost and efficient UV irradiation is pro-vided by a bank of total twelve 40 W black lamps (peakintensity at 350 nm) mounted on the wall of aluminumenclosure. Each lamp can be controlled separately sothat light intensity can be adjusted in different levelsaccording to the requirements of the experiments.

B. Component injection system

Pure air is generally used as carrier gas for primarycomponents injected to the chamber in our experiments.As shown in Fig.2, the pure air system consists of anair compressor, drying system, particle filtering system,and zero air supply (AADCO 737-15, USA); and thecorresponding parameters of these parts are briefly de-scribed in Table I. The pure air system can supply puri-fied air with no detectable non-methane hydrocarbons(NMHC<1 ppb), NOx (<1 ppb), low O3 concentration(<1 ppb), low particle densities (<5 particles/cm3), and<5% relative humidity (RH) at rate up to 40 L/min atpressure of 30 psi.

As shown in Fig.1, gaseous components (such as NOx

and NH3) are carried by purified air and supplied tothe chamber directly. While O3 is generated by passingthe purified air through a corona discharge O3 gener-ator, wherein flow rates and time can be controlled toprovide O3 of ppb to ppm mixing ratios in the cham-ber. Liquid parent hydrocarbon (for example, isopreneor α-pinene) is firstly evaporated in a 250 mL glasssampling bulb, which is wrapped in a temperature-controlled heater (50−300 ◦C), and then flushed intothe chamber by purified air. A particle generation sys-tem (TSI, model 3940, USA) is available for seed parti-cle experiments, which consists of a constant output at-omizer (TSI, model 3076, USA), a diffusion dryer (TSI,model 3062, USA), and an aerosol charge neutralizer(TSI, model 3077, USA). The dry seed particles with acertain concentration and size distribution can be ob-tained by controlling the concentration of the solutionand the injection time.

C. Detection system

The commercial instruments used to monitor gaseousspecies and aerosol particles within the reactor are listedand briefly described in Table II.



TABLE II The commercial analytical instruments of the smog chamber.

Instrument Model Measurement Range Accuracy

Temperature and Vaisala HMT333 Temperature −40 ◦C to 80 ◦C ±0.2 ◦C

Humidity Sensor Relative humidity 0–100% ±1%

NH3 analyzer TEI model 17i NO, NO2, NOx, NH3 0−100 ppm ±0.5 ppb

SO2 analyzer TEI model 43i SO2 0−1000 ppb ±0.2 ppb

O3 analyzer TEI model 49i O3 0−200 ppm ±1.0 ppb

GC-FID Agilent 7820A VOCs 12 ppb

SMPS TSI 3080L DMA Aerosol number and size distribution 1−107 cm−3 Adequate

TSI 3775 CPC Aerosol number and size distribution 14−673 nm

The temperature and RH in the smog chamber aredetected continually by a temperature and humiditysensor (Vaisala HMT333, Finland). The concentrationsof O3, NO (NO2, NOx, NH3), and SO2 are measuredin real time by ozone analyzer (TEI, model 49i, USA),NH3 analyzer (TEI, model 17i, USA) and SO2 analyzer(TEI, model 43i, USA) respectively. Generally, hydro-carbons (especially the precursors of SOA) are moni-tored by gas chromatography-flame ionization detector(GC-FID, Agilent 7820A, USA) equipped with an HP-5capillary column (30 m×0.32 mm×0.25 µm film thick-ness). The gaseous species in the smog chamber aresampled by the six-port stainless steel injection valveequipped with a heated (150 ◦C) 0.25 mL Teflon sam-pling loop, and the GC temperature program is as fol-lows: 50 ◦C for 0.5 min, 50−150 ◦C at 40 ◦C/min.The calibration of the concentration of HCs was per-formed prior to each experiment by vaporizing somemicroliter volumes of a sample solution into an 80 LTeflon bag filled with a determined volume of pure air[25]. The size distribution and number concentrationof aerosol particles are monitored using a scanning mo-bility particle sizer (SMPS), which consists of a TSImodel 3077 85Kr neutralizer, a TSI model 3081 long col-umn cylindrical differential mobility analyzer (DMA),and a TSI model 3775 condensation particle counter(CPC). In general, the SMPS is operated at a rate of135 s/scan. While DMA operates with sheath at flowrate of 3.0 L/min and aerosol sample at flow rate of0.3 L/min, and the corresponding column voltage is ex-ponentially ramped from −10 V to −9591 V to allowfor measurable particle mobility size distribution in therange of 14−673 nm.

The smog chamber is also characterized by severalfeatured home-made instruments besides the aforemen-tioned traditional instruments. A Chernin multipasscell system has been developed and combined with thesmog chamber in our group for measurement of VOCsbased on absorption spectroscopy in ultraviolet-visiblerange. The details of the principle, design, and applica-tion of the cell have been described previously [26, 27].Briefly, the optical path-length can be adjusted from3 m to 330 m, and its detection limit is 19.1 µg/m3 for

NO2 with 37 m absorption path-length.

As a non-dissociative ionization technique based onproton transfer reactions to ionize organic components,proton transfer reaction mass spectrometer (PTR-MS)was developed originally for trace gas analysis [28] andapplyed in research on atmospheric photochemical reac-tion within environmental reaction smog chambers [18].A high sensitive PTR-MS has been constructed recently[29] and has also been cooperated with the smog cham-ber for on-line measurements of gaseous componentswithin the chamber. The mass spectrometer consists ofan ion source (H3O

+ is used as the proton donor), anion-molecule reaction flow tube, and a mass spectrumdetection system. And its detection limit is around10−8 based on the primary ion intensity, ion reactiontime, and instrumental parameters.

With regard to its tunability in the ultraviolet (UV)and vacuum ultraviolet (VUV) energy range and high-intensity photons, synchrotron radiation (SR) is well-known as one of the best fragment-free, single-photonphotoionization sources for a “soft” ionization method.A VUV photoionization mass spectrometer based on SR[30] has been combined with the smog chamber for thefirst time very recently in our group [31]. Generally,the mass spectrometer is operated at the energy region7.5−22.4 eV, which is enough to ionize almost all gascomponents within the chamber. In view of the particu-lar advantage of SR photoionization mass spectrometry,which is universal to the detected molecules based onthe ionization energy (IE) of molecules and can deter-mine molecular composition further by photoionizationefficiency (PIE) curve although not with only the m/zratio, it is believed that the technique may find a widerange of applications in the study on atmospheric oxi-dation and formation of SOA.

On-line detection of size distribution and analysis ofchemical composition of aerosol particles are prerequi-site to study atmospheric photochemical processes andformation of secondary organic aerosol (SOA). However,the traditional methods, such as SMPS and GC-MS,can only be competent for one way. To overcome thosedisadvantages, an aerosol time of flight mass spectrom-eter was designed [32] and employed to detect the par-



ticle phase generated in the reaction chamber, whichallow real-time measurement of the size and chemicalcomposition of individual aerosol particle. The massspectrometer can measure aerosol particle with the sizelow to 100 nm at an average 10% hit rate of ionization,and has a mass resolution high to 1510 at m/z=913[33].

D. Auto-control and data acquisition system

A computer auto-control and data acquisition sys-tem is used to acquire, process, and record data fromthe detection instruments. And the software is pro-grammed by using Labview. The analog signals fromO3 analyzer, NH3 analyzer, SO2 analyzer, and tem-perature and humidity sensor are firstly converted todigital through a 12 bits analog to digital (AD) conver-sion chip and then recorded by personal computer. Toreduce the consumption volume of the samples withinthe chamber, gaseous components or aerosol particlesare sampled at regular intervals. This working mode isperformed by using computer-controlled three-way elec-tromagnetic valves installed between the chamber andthe detection instruments. The program permits thesetting of time sampling sequences and data logging ac-cording to the experimental requirements.

III. CHARACTERIZATION OF THE SMOG CHAMBER

Characterization of the smog chamber was performedin order to obtain the fundamental parameters, such astemperature, relative humidity, irradiation light, back-ground reactivity of background gases, wall loss ratesof gas reactants and particles.

A. Characterization of temperature and ultraviolet lightintensity

In order to mimic ground-level sunlight with clearsky conditions in UV region, blacklights were chosen asirradiation source in our chamber. The emission spec-trum of blacklight (peak intensity at 350 nm) is shownin Fig.3, as well as the representative solar spectrum(z=0). Figure 4 shows the characterization of tem-perature in the smog chamber when 10 blacklights areturned on. It seems that after the initial increasing,the temperature inside the smog chamber keeps nearlystable around 24.5±0.2 ◦C in the following time duringour experiment.

It is well known that the following reactions will beinitiated under ultraviolet light [34]:

NO2 + hνk1→ NO+O· (1)

O·+O2k2→ O3 (2)

NO +O3k3→ NO2 +O2 (3)

FIG. 3 Spectra of blacklight and solar (z=0).

FIG. 4 The evolution of temperature in smog chamber.

So the photolysis rate of NO2, k1, can be used as an in-dex of the light intensity inside the chamber. When theresulting NO, NO2, and O3 mixing ratios in the smogchamber are measured, the photolysis rate constant, k1,can be estimated as k1=k3[NO][O3]/[NO2] [15], wherek3 is calculated from the Arrhenius equation as follows:

k3(T ) = A exp

(−E

R

1

T

)(4)

where A and E/R are 2.0×10−12 and 1.4×102 respec-tively [34]. The photolysis of NO2 in this smog chamberis shown in Fig.5, and the measured k1 value in the smogchamber at full light intensity is 0.21 min−1.

B. Reactivity of pure air

In order to evaluate the background reactivity, thecharacterization experiment was carried out under blackcondition with no reactive VOCs but 224 ppb O3 andthe purified air being added into the chamber. As shownin Fig.6, total particle number concentration was lessthan 10 particle/cm3 and total particle mass was lessthan 0.1 µg/m3 during 4 h experiment, nearly the sameas the background level. Compared with the photoox-idation of VOCs, wherein the particle number concen-tration and particle mass are generally 105 particle/cm3



FIG. 5 The light intensity measured by the photolysis rate.The initial concentration of NO2 was 200 ppb.

FIG. 6 Particle size distribution in smog chamber duringbackground reactivity experiment.

and 102 µg/m3, respectively, the formation of particlesin pure air irradiations can be ignored in this chamber.

C. Wall loss of particle and gaseous compounds

According to the partitioning theory originally out-lined by Pankow [35, 36] and Odum et al. [37], SOAyield Y is defined as the ratio of the amount of SOAformed to the amount of hydrocarbon consumed,

Y =∆M0

∆HC(5)

where ∆M0 (µg/m3) is the mass of organic aerosolformed by the oxidation of ∆HC (µg/m3). Accuratedetermination of the SOA yield requires correction ofwall losses.

Particle wall losses are always expected in finitevolume reactors and are somewhat enhanced by thecharged surfaces of the Teflon media. It is believedthat the loss of particles to the wall of the chamberis the principal process that complicates the interpre-tation of measured aerosol data. Particle depositiononto the wall of the chamber is the net result of tur-bulent, Brownian diffusion, gravitational sedimentationand also a function of the particle size [38]. In orderto determine the deposition rate of the aerosol, decay

of the (NH3)2SO4 aerosol was investigated under darkcondition. The observations were conducted at low par-ticle concentration (∼103 particle/cm3) to avoid the co-agulation. Particle wall loss can be described as a firstorder process dependent on a particle loss coefficient,kdep(dp),

dN(dp)

dt= −kdep(dp)N(dp) (6)

where N(dp) is the concentration of particles andkdep(dp) is the loss coefficient for particles with diame-ter dp [15].

Figure 7(a) shows the deposition rate constant of theparticle as a function of its diameter measured in thischamber. Regarding to the irregular geometry of thechamber in this work, we tried to determine the re-lationship between kdep and dp by optimization of fourparameters (a, b, c, and d) according to empirical Eq.(7)[16].

kdep(dp) = adpb +

c

dpd

(7)

The optimized line well expressed the experimentaldata, and the parameters a, b, c, and d were optimizedto be 4.17×10−13, 4.66, 10.18, and 0.75 respectively. Asfor the smaller volume of this chamber, it is reasonableto find that the decay of the aerosol with bigger sizein this chamber is faster than that of TCRDL [16] andTSC [23]. For example, for the aerosol with 150 nm ofdp, kdep is calculated to be 30.0%/h for our chamber,whereas 10.3%/h for TCRDL [16] and 6.74%/h for TSC[23]. Based on the measurement of the deposition rateconstant of the particle, the wall effect for aerosol par-ticles of this chamber has been corrected well (as shownin Fig.7 (b) and (c)).

The wall loss of gaseous compounds of the chamber,especially reactive VOCs, was also evaluated. α-pinenehas been chosen as a test sample. In the trial, the initialα-pinene concentration was 2122 ppb, and the resultingconcentration was still 2118 ppb after 3 h. Therefore,the wall loss of HCs is negligible in this chamber.

IV. INITIAL EXPERIMENTS

A. α-Pinene/O3 SOA yield

In our recent work, we have demonstrated the ap-plicability of the chamber on the study of SOA sizedistributions and formation rates from photo-oxidationof isoprene with organic seed [39]. Based on the to-tal aerosol volume measured by SMPS, total mass ofSOA can be calculated as its average density has beendetermined.

In order to evaluate the reproducibility of the cham-ber, a series of α-pinene/O3 experiments were per-formed under dark condition and the results were com-pared with those carried out in Caltech [15], and arelisted in Table III and shown in Fig.8.



FIG. 7 Evaluation of wall loss of the chamber. (a) The deposition rate efficient (kdep) of the particles as a function ofparticle diameter. (b) An example of the evolution of particle size distribution (raw data). (c) The evolution of particle sizedistribution (corrected data based on the measurement of kdep shown in Fig.7(a)).

TABLE III Conditions and summary of the α-pinene/O3

system SOA yield experiments (∆ROG and ∆M0 in µg/m3

and [O3] in ppb).

No. ∆ROGa ∆M0b [O3] RH/% Tavg/K Yield

1 1363 313 225 9 299 0.230

2 467 61 93 8 298 0.131

3 1062 220 180 8 298 0.242

4 1385 335 213 11 298 0.261

5 1680 439 244 10 298 0.207

Caltech-1 398.5 80 270 <2 301 0.201

Caltech-2 225.2 35 278 <2 302 0.155

Caltech-3 512.5 110 499 <2 302 0.215

Caltech-4 888.5 220 175 <2 303 0.248

Caltech-5 762.6 185 380 <2 303 0.243a Reactive organic gas (ROG) concentration reacted.b Generated mass concentration of the SOA (corrected forwall loss).

The data are analyzed according to the originalschemes outlined by Pankow [35, 36] and Odum et al.[37]. Following the semiempirical product model, SOAyield Y , can be expressed as

Y = M0

∑i

αiki1 + kiM0

(8)

where αi is the mass-based stoichiometric fraction ofspecies i formed from the parent hydrocarbon, ki is thegas-particle partitioning coefficient, and M0 is the totalmass concentration of organic material. As shown inFig.8, the yield data of our chamber have shown essen-tial agreement with those of Caltech chamber, whichverified the ability of the new chamber to accuratelysimulate gas-particle conversion processes. It is worthpointing out that the yield in our work is a little lower.Regarding to the relative humidity as one of the impor-tant factors in SOA formation [40], however, it is rea-sonable that the SOA yield of this chamber (RH=10%)

FIG. 8 Comparison of yield data obtained for the α-pinene/O3 system in this work with that of Caltech underblack condition.

is less than the yield of Caltech (RH<2%).

B. Measurement of products chemical composition

The determination of chemical composition of gasor particle phase products resulting from oxidation ofVOCs is pivotal to learning the formation, propertiesand impact of SOA. And it covers a wide range of an-alytical techniques. Compared to off-line techniques,which often create the inherent risk of artifacts due toadsorption, evaporation, and chemical reactions duringthe multi-step collection and analysis procedure, on-linetechniques have revolutionized the chemical analysis ofproducts by providing real-time measurements. Gener-ally, the complexity of the organic component and thestrong fragmentation of molecular ion species in tradi-tional MS make it very difficult to identify unambigu-ously the chemical composition of the gaseous or parti-cle phase products from atmospheric oxidation.

It is believed that both PTR-MS and SRPIMS arefeatured for their “soft” ionization and the other prop-erties, such as high mass resolution, high sensitivity andability to discriminate the isomers. In this work, gas



FIG. 9 Mass spectra of products from isoprene/CH3ONO/air system photochemical reaction. (a) PTR-MS for gas products,(b) SRPIMS for gas products at the photon energy of 15 eV, (c) ALTOFMS for particle products.

phase products produced from isoprene/CH3ONO/airphotooxidation system have been detected and ana-lyzed on-line by PTR-MS and SRPIMS respectively.As shown in Fig.9, C4H6O (m/z=70) is detected asa major gas phase product from OH initiated isoprenephotooxidation reaction in the two different kinds ofMS (Fig.9 (a) and (b)). Further work proves that twoisomers, methacrolein (MACR) and methyl vinyl ke-tone (MVK), are candidates for m/z=70 components.While the further oxidation of MACR is responsible forthe formation of SOA, the oxidation of MVK makes nocontribution to the formation of SOA.

Aerosol laser time-of-flight mass spectrometry (AL-TOFMS) is notable for the capability of the simul-taneous determination of both the size and chemicalcomposition of individual particle in real-time [41]. Anaerosol laser time-of-flight mass spectrometer has alsodeveloped in our group and its cooperation with smogchamber in the study on photooxidation of the aro-matic hydrocarbon has been demonstrated previously[42, 43]. In this work, particle phase products pro-duced from isoprene/CH3ONO/air photooxidation sys-tem are also detected on-line by ALTOFMS. As shownin Fig.9(c), the components m/z=120 has been foundpartition in particle phase, which is attentively assignedas 2-methylglyceric acid (2-MG). As it was found re-cently that a series of oligomers involving 2-MG arerelated with the formation of SOA, 2-MG is believedto act as SOA tracer compound for isoprene oxidationin the ambient atmosphere [44–46]. Although morework is needed to analyze the whole features in thismass spectra, the results obtained here show reason-able agreement with those investigated by using differ-ent kinds of techniques in the other laboratories [47].

V. CONCLUSION

A state-of-the-art smog chamber is designed and con-structed for investigation of atmospheric chemistry inthis work. Useful analytical techniques, such as PTR-MS, SRPIMS, and ALTOFMS, have been developed

and employed to the smog chamber system for on-linemeasurement of gas and particle products of VOCs ox-idation. A series of characterization and evaluation ex-periments has been carried out, which shows generalagreement with other work and good reproducibilityof the chamber. Although only the primary data areshown here, the ability to accurately and precisely studygas-phase chemical mechanisms and SOA formation ofthis chamber facility is demonstrated.

VI. ACKNOWLEDGMENTS

This work was supported by the NaturalScience Foundation of Anhui Province, China(No.1208085MD59), the National Natural ScienceFoundation of China (No.U1232209, No.41175121, andNo.21307137), the Presidential Foundation of HefeiInstitutes of Physical Science, Chinese Academy ofSciences, China (No.YZJJ201302), and the KnowledgeInnovation Foundation of the Chinese Academy ofSciences (No.KJCX2-YW-N24).

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