Characterization of Organic Aerosols in Beijing Using an Aerodyne High-Resolution Aerosol Mass Spectrometer

Fine particle of organic aerosol （OA）, mostly arising from pollution, are abundant in Beijing. To achieve a better un- derstanding of the difference in OA in summer and autumn, a high-resolution time-of-flight aerosol mass spectrometer （HR- ToF-AMS, Aerodyne Research Inc., USA） was deployed in urban Beijing in August and October 2012. The mean OA mass concentration in autumn was 30 4-30 μg m-3, which was higher than in summer （13 4-6.9 μg m-3）. The elemental anal- ysis found that OA was more aged in summer （oxygen-to-carbon （O/C） ratios were 0.41 and 0.32 for summer and autumn, respectively）. Positive matrix factorization （PMF） analysis identified three and five components in summer and autumn, re- spectively. In summer, an oxygenated OA （OOA）, a cooking-emission-related OA （COA）, and a hydrocarbon-like OA （HOA） were indentified. Meanwhile, the OOA was separated into LV-OOA （low-volatility OOA） and SV-OOA （semi-volatile OOA）; and in autumn, a nitrogen-containing OA （NOA） was also found. The SOA （secondary OA） was always the most important OA component, accounting for 55% of the OA in the two seasons. Back trajectory clustering analysis found that the origin of the air masses was more complex in summer. Southerly air masses in both seasons were associated with the highest OA loading, while northerly air masses were associated with the lowest OA loading. A preliminary study of OA components, especially the POA （primary OA）, in different periods found that the HOA and COA all decreased during the National Day holiday period, and HOA decreased at weekends compared with weekdays.

Pollutants identification of ambient aerosols by two types of aerosol mass spectrometers over southeast coastal area, China

Two different aerosol mass spectrometers, Aerodyne Aerosol Mass Spectrometer（AMS） and Single Particle Aerosol Mass Spectrometer（SPAMS） were deployed to identify the aerosol pollutants over Xiamen, representing the coastal urban area. Five obvious processes were classified during the whole observation period. Organics and sulfate were the dominant components in ambient aerosols over Xiamen. Most of the particles were in the size range of 0.2–1.0 μm, accounting for over 97% of the total particles measured by both instruments.Organics, as well as sulfate, measured by AMS were in good correlation with measured by SPAMS. However, high concentration of NH4＋was obtained by AMS, while extremely low value of NH4＋was detected by SPAMS. Contrarily, high particle number counts of NO3-and Clwere given by SPAMS while low concentrations of NO3-and Cl-were measured by AMS. The variations of POA and SOA obtained from SPAMS during event 1 and event 2 were in accordance with the analysis of HOA and OOA given by AMS, suggesting that both of AMS and SPAMS can well identify the organic clusters of aerosol particles. Overestimate or underestimate of the aerosol sources and acidity would be present in some circumstances when the measurement results were used to analyze the aerosol properties, because of the detection loss of some species for both instruments.

Chemical composition and size distribution of secondary organic aerosol formed from the photooxidation of isoprene

Photooxidation of isoprene leads to the formation of secondary organic aerosol （SOA）. In this study, the chemical composition of SOA formed from OH-initiated photooxidation of isoprene has been investigated with gas chromatography/mass spectrometry （GC/MS） and a home-made aerosol time-of-fiight mass spectrometer. Sampling particles generated in a home-made smog chamber. The size distribution of SOA particles was detected by a TSI 3321 aerodynamic particle size spectrometer in real time. Results showed that SOA created by isoprene photooxidation was predominantly in the form of fine particles, which have diameters less than 2.5 μm. The obtained mass spectra of individual particles show that products of the OH-initiated oxidation of isoprene contain methyl vinyl ketone, methacrolein, formaldehyde, and some other hydroxycarbonyls. The possible reaction mechanisms leading to these products were also discussed.

Characterization of submicron aerosols in the urban outflow of the central Pearl River Delta region of China

Submicron aerosol particles （with aerody- namic diameters less than 1 pm, PM1） were sampled and measured in Heshan, an urban outflow site of Guangzhou megacity in Pearl River Delta in South China, using an Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer （HR-ToF-AMS） in November 2010 during 2010 Guangzhou Asian Games. The mean PM~ mass concentration measured was 47.9 ± 17.0 μg.m3 during the campaign, with organic aerosol （OA） and sulfate being the two dominant species, accounting for 36.3% and 20.9% of the total mass, respectively, followed by black carbon （17.1%, measured by an aethalometer）, nitrate （12.9%）, ammonium （9.6%） and chloride （3.1%）. The average size distributions of the species （except black carbon） were dominated by an accumulation mode peaking at -550 nm. Calculations based on high-resolution organic mass spectrum showed that, C, H, O and N on average contributed 58.1%, 7.3%, 30.7%, and 3.9% to the total organic mass, respectively. The average ratio of organic mass over organic carbon mass （OM/OC） was 1.73 ± 0.08. Four components of OA were identified by the Positive Matrix Factorization （PMF） analysis, including a hydro- carbon-like （HOA）, a biomass burning （BBOA） and two oxygenated （SV-OOA and LV-OOA） organic aerosol components, which on average accounted for 18.0%, 14.3%, 28.8% and 38.9% of the total organic mass, respectively.

Single particle analysis of ambient aerosols in Shanghai during the World Exposition,2010:two case studies

ATSI Model 3800 aerosol time-of-flight mass spectrometer(ATOFMS)was deployed for single-particle analysis in Shanghai during theWorld Exposition(EXPO),2010.Measurements on two extreme cases:polluted day(1st May)and clean day(25th September)were compared to show how meteorological conditions affected the concentration and composition of ambient aerosols.Mass spectra of 90496 and 50407 particles were analyzed respectively during the two sampling periods.The ART-2a neural network algorithm was applied to sort the collected particles.Seven major classes of particles were obtained:dust,sea salt,industrial,biomass burning,organic carbon(OC),elementary carbon(EC),and NH4-rich particles.Number concentration of ambient aerosols showed a strong anti-correlation with the boundary layer height variation.The external mixing states of aerosols were quite different during two sampling periods because of different air parcel trajectories.Number fraction of biomass burning particles(43.3%)during polluted episode was much higher than that(21.6%)of clean time.Air parcels from the East China Sea on clean day diluted local pollutant concentration and increased the portion of sea salt particle dramatically(13.3%).The large contribution of biomass burning particles in both cases might be an indication of a constant regional background of biomass burning emission.Mass spectrum analysis showed that chemical compositions and internal mixing states of almost all the particle types were more complicate during polluted episode compared with those observed in clean time.Strong nitrate signals in the mass spectra suggested that most of the particles collected on polluted day had gone through some aging processes before reaching the sampling site.

Homogeneous and heterogeneous reactions of anthracene with selected atmospheric oxidants

The reactions of gas-phase anthracene and suspended anthracene particles with O3 and O3-NO were conducted in a 200-L reaction chamber, respectively. The secondary organic aerosol （SOA） formations from gas-phase reactions of anthracene with O3 and O3-NO were observed. Meanwhile, the size distributions and mass concentrations of SOA were monitored with a scanning mobility particle sizer （SMPS） during the formation processes. The rapid exponential growths of SOA reveal that the atmospheric lifetimes of gas-phase anthracene towards O3 and O3-NO are less than 20.5 and 4.34 hr, respectively. The particulate oxidation products from homogeneous and heterogeneous reactions were analyzed with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer （VUV-ATOFMS）. Gas chromatograph/mass spectrometer （GC/MS） analyses of oxidation products of anthracene were carried out for assigning the time-of-flight （TOF） mass spectra of products from homogeneous and heterogeneous reactions. Anthrone, anthraquinone, 9,10- dihydroxyanthracene, and 1,9,10-trihydroxyanthracene were the ozonation products of anthracene, while anthrone, anthraquinone, 9-nitroanthracene, and 1,8-dihydroxyanthraquinone were the main products of anthracene with O3-NO.