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By taking advantage of recent advances in High-Resolution Atmospheric Pressure intake Time of Flight (APi–TOF) Mass Spectrometry (MS), the chemical analysis of naturally charged flame-generated soot nuclei and precursors is explored using a well-characterized dilution sampling approach. Measurements were performed for mass-to-charge ratio up to 2000 Thomson, bridging the gap between the gas phase and the particle phase. The flame products were sampled at several heights above the burner (HAB) in the soot inception zone of the flame, quickly diluted in nitrogen and directly transported to the APi–TOF inlet. The investigated sooting premixed flame has been the object of multiple studies over the years and the present results complement existing literature data. The analyses of flame products naturally carrying charge of either polarity revealed the chemical and polarity-dependent complexity of the nucleation and chemi-ionization processes. The measured high-resolution mass spectra include peaks attributed to (hydrocarbon) molecules/clusters containing oxygen and nitrogen atoms and suggest that collision charging of flame pyrolysis products likely involves protonation/deprotonation of neutral materials. Results clearly show the change of the overall composition of the charged flame products at different HABs. Patterns in the mass spectra under different conditions were investigated to discriminate between collision charging, chemical reaction and physical clustering (i.e., coagulation and condensation) growth mechanisms. A comparison of the results with those obtained with High-resolution Differential Mobility Analysis (HR-DMA) in a recent study allowed for a more quantitative determination of the ion number concentrations.

We present laboratory measurements of the chemical speciation of black carbon particles produced from burning a series of biomass fuels during FLAME III (2009). A soot particle aerosol mass spectrometer (SP-AMS) was utilized to study the chemical composition of refractory black carbon particles and the associated nonrefractory components. We examine the effect of source fuel and combustion efficiency on the chemical composition of the emitted black carbon aerosol particles. Fifteen different source fuel types were examined. Two distinct types of black carbon spectra were observed: Low mass to charge (C1+-C5+) black carbon cluster ions were observed for all fuels while high mass to charge (>C32+) black carbon cluster ions with distinctive fullerene structure were found for turkey oak and pine species. The relative ratios between the mass concentrations of non-refractory organic species and black carbon varied between fuel types and displayed an inverse correlation with the modified combustion efficiency (MCE) of the burns. Finally, positive matrix factorization (PMF) was conducted on the SP-AMS mass spectra in order to examine the variability in the chemical composition of the observed biomass burning particles and to identify potential signatures of different fuel types.

The Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was redeployed at the Jefferson Street (JST) site in downtown Atlanta, Georgia (GA) for 1 year (March 20, 2014–February 08, 2015) to chemically characterize non-refractory submicron particulate matter (NR-PM1) in near real-time and to assess whether organic aerosol (OA) types and amounts change from year-to-year. Submicron organic aerosol (OA) mass spectra were analyzed by season using multilinear engine (ME-2) to apportion OA subtypes to potential sources and chemical processes. A suite of real-time collocated measurements from the Southeastern Aerosol Research and Characterization (SEARCH) network was compared with ME-2 factor solutions to aid in the interpretation of OA subtypes during each season. OA tracers measured from high-volume filter samples using gas chromatography interfaced with electron ionization-mass spectrometry (GC/EI-MS) also aided in identifying OA sources. The initial application of ME-2 to the yearlong ACSM dataset revealed that OA source apportionment by season was required to better resolve sporadic OA types. Spring and fall OA mass spectral datasets were separated into finer periods to capture potential OA sources resulting from non-homogeneous emissions during transitioning periods. NR-PM1 was highest in summer (16.7 ± 8.4 μg m−3) and lowest in winter (8.0 ± 5.7 μg m−3), consistent with prior studies. OA dominated NR-PM1 mass (56–74% on average) in all seasons. Hydrocarbon-like OA (HOA) from primary emissions was observed in all seasons, averaging 5–22% of total OA mass. Strong correlations of HOA with carbon monoxide (CO) (R = 0.71–0.88) and oxides of nitrogen (NOx) (R = 0.55–0.79) indicated that vehicular traffic was the likely source. Biomass burning OA (BBOA) was observed in all seasons, with lower contributions (2%) in summer and higher in colder seasons (averaging 8–20% of total OA mass). BBOA correlated strongly with levoglucosan (R = 0.78–0.95) during colder seasons, which supports that BBOA is likely derived from fresh biomass/residential burning. However, weaker correlation with levoglucosan (R = 0.38) in summer suggested a more aged aerosol. During warmer seasons, OA from the reactive uptake of isoprene epoxydiols (IEPOX) onto acidic sulfate aerosol was resolved by ME-2 (denoted as IEPOX-OA), averaging 25–29% of the total OA mass. Temporal variation of IEPOX-OA was nearly coincident with that of 91Fac OA (a factor dominated by a distinct ion at m/z 91). The largest contribution of IEPOX-OA to total OA (29%) was found in summer, whereas the largest contribution of 91Fac to total OA (24%) occurred in early fall. Moderate negative correlation between IEPOX-OA and aerosol acidity was observed during late spring (−0.67) and summer (−0.42), consistent with laboratory studies showing that IEPOX-OA is enhanced in the presence of acidic aerosols. Finally, the largest OA mass in all seasons (46–70% of total OA) was derived from oxygenated OA denoted as low-volatility oxygenated OA (LV-OOA) and semi-volatile oxygenated OA (SV-OOA).

This study introduces an atmospheric pressure chemical ionization method that relies on low-energy thermal collisions (i.e.

The resolution of mass spectrometers is often insufficient to conclusively identify all peaks that may be present in recorded spectra. Here, we present new methods to extract consistent molecular and bulk level chemical information by constrained fitting of series of complex organic mass spectra with multiple overlapping peaks. Possible individual peaks in a group of overlapping peaks are identified by both defining a chemical space and by free peak fitting. If simply all possible formulas from the chemical space would be used to fit each peak, the result would not be well constrained. The free peak fitting algorithm provides information about likely peak locations. A new algorithm then reconciles the results of both methods and produces a final peak list for use in subsequent fitting, while using all available experimental constraints. Comparison to ultra-high resolution data suggests that the real peak density is substantially higher than can be resolved with the instrument resolution. Bulk chemical properties such as carbon number (nC) and carbon oxidation state (OS C ) can be calculated from the fit results. For mixtures of compounds dominated by C, H, O and N, bulk properties can be reliably extracted, even though some formula assignments may remain uncertain. This ability to retrieve correct bulk parameters even if not all assigned formulas are correct originates from the relationship between mass defects of individual peaks and the chemical parameters under our CHON composition assumptions. Retrieving consistent bulk parameters across series of many mass spectra is essential for extracting time trends, e.g. for field measurements taking place over several weeks. We illustrate the fitting method using a sample data set from a chemical ionization mass spectrometer with a resolution of approximately 4000 (M/dM), operated using acetate reagent ions. Spectral simulation experiments validate the analysis method by showing good agreement of intensities for many specific ions, as well as for bulk chemical parameters. An alternative method to directly extract bulk chemical information from the raw spectra without the need of any peak assignment or peak fitting is also introduced, which shows good agreement with the peak fitting results. The latter method can be applied very rapidly without the need for complex analysis procedures, e.g. as a quick online diagnostic during data acquisition.

An Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was first deployed in Beijing, China for characterization of summer organic and inorganic aerosols. The non-refractory submicron aerosol (NR-PM1) species, i.e., organics, sulfate, nitrate, ammonium, and chloride were measured in situ at a time resolution of ∼15 min from 26 June to 28 August, 2011. The total NR-PM1 measured by the ACSM agrees well with the PM2.5 measured by a Tapered Element Oscillating Microbalance (TEOM). The average total NR-PM1 mass for the entire study is 50 ± 30 μg m−3 with the organics being the major fraction, accounting for 40% on average. High concentration and mass fraction of nitrate were frequently observed in summer in Beijing, likely due to the high humidity and excess gaseous ammonia that facilitate the transformation of HNO3 to ammonium nitrate particles. Nitrate appears to play an important role in leading to the high particulate matter (PM) pollution since its contribution increases significantly as a function of aerosol mass loadings. Positive matrix factorization (PMF) of ACSM organic aerosol (OA) shows that the oxygenated OA (OOA) – a surrogate of secondary OA dominates OA composition throughout the day, on average accounting for 64%, while the hydrocarbon-like OA (HOA) shows a large increase at meal times due to the local cooking emissions. Our results suggest that high PM pollution in Beijing associated with stagnant conditions and southern air masses is characterized by the high contribution of secondary inorganic species and OOA from regional scale, whereas the aerosol particles during the clean events are mainly contributed by the local emissions with organics and HOA being the dominant contribution.

Observations from four periods (three late springs and one early summer) at temperate forest sites in western and eastern Canada offer the first estimation of how the concentrations of submicron forest organic aerosol mass (SFOM) from the oxidation of biogenic volatile organic compounds (BVOC) vary over the ambient temperature range of 7 °C to 34 °C. For the measurement conditions of clear skies, low oxides of nitrogen and within approximately one day of emissions, 50 estimates of SFOM concentrations show the concentrations increase exponentially with temperature. The model that is commonly used to define terpene emissions as a function of temperature is able to constrain the range of the SFOM values across the temperature range. The agreement of the observations and model is improved through the application of an increased yield of SFOM as the organic mass concentration increases with temperature that is based on results from chamber studies. The large range of SFOM concentrations at higher temperatures leaves open a number of questions, including the relative contributions of changing yield and of isoprene, that may be addressed by more ambient observations at higher temperatures.

A metastable atom bombardment (MAB) ionization source has been coupled to an existing thermal desorption aerosol mass spectrometer. The design allows real-time alternation between MAB and electron ionization (EI). A jet of metastable species produced in a DC discharge is directed at the ionization volume of the mass spectrometer, where Penning ionization is thought to be the dominant mechanism. Performance is characterized in experiments with oleic acid particles. By changing discharge gases between N 2 , Kr, and Ar, the excited state energy of the metastable species can be adjusted in the range 8.5–11.7 eV. For vaporization at 180 °C, all gases yield significantly less fragmentation than EI, which could improve results of factor analysis. Fragmentation increases with vaporization temperature, but generated fragments have higher average mass than those produced by EI. Analyte signal levels are 0.1% and 0.006% of equivalent analysis with EI when using Ar * and Kr * , respectively. These sensitivities are not practical for ambient studies, but are sufficient for source measurements, as demonstrated with direct measurements of biomass burning emissions. The measured Ar * flux of 3.6 × 10 13 sr −1 s −1 is ∼30 times lower than the best literature values for similar metastable beam sources, suggesting that sensitivity can be increased by source design improvements.

Atmospheric aerosols are a major pollutant in Beijing—a megacity in China. To achieve a better understanding of the characteristics, sources and processes of aerosols in Beijing, an Aerodyne Aerosol Mass Spectrometer (AMS) was deployed at an urban site in July 2006 to obtain size-resolved chemical composition of non-refractory submicron particles (NR-PM 1 ) at 5 min resolution. During this study, NR-PM 1 was on average composed of 25% sulfate, 22% nitrate, 16% ammonium, 1.4% chloride and 35% of organic aerosol (OA) species. The average size distributions of sulfate, nitrate and ammonium were very similar and characterized by a prominent accumulation mode peaking at D va ≈ 600 nm. The average size distribution of OA was significantly broader due to the presence of an ultrafine mode. Multivariate analysis of the AMS organic spectra with Positive Matrix Factorization (PMF) identified a hydrocarbon-like OA (HOA) and two oxygenated OA (OOA) components. The HOA component likely corresponded to primary OA material associated with combustion-related emissions. The two OOA components, which likely corresponded to more oxidized (OOA I) and less oxidized (OOA II) secondary OA materials, accounted for 45 ± 16% and 16 ± 7.2%, respectively, of the observed OA mass. OOA I correlated well with sulfate while OOA II correlated well with nitrate. The particle loading, composition and size distributions observed during this campaign were highly variable. Backtrajectory analysis indicates that this variability correlated with the varying impacts of regional and local sources and processes.

Time series measurements of the size and composition of aerosol particles made near Ocean Station Papa during the Canadian SOLAS SERIES experiment in July 2002 indicate major contributions to the aerosol mass from the oxidation of dimethyl sulphide, from primary emissions of sea salt, and from ship emissions. The high temporal resolution of the AMS revealed significant variability in the fine mode species mass concentrations in this area. The background fine mode composition was dominated by non-sea-salt-sulphate (nss-SO4), sea salt, organics, and methanesulphonic acid (MSA), with average mass concentrations of 0.74±0.04, 0.6±0.1, 0.3±0.1, and 0.16±0.05 μg m−3, respectively. The fine mode MSA:nss-SO4 ratio varied from 0.01 to 3.19±0.2, with a mean of 0.23. The average fine mode mass distribution was internally mixed with a mode vacuum aerodynamic diameter of 475 nm. The concentration of MSA was an order of magnitude higher than previously reported values in the North Pacific, indicating significant oxidation of DMS. A diurnal signal in particulate products of DMS oxidation (i.e. MSA and sulphate) and in gaseous DMS and SO2 indicates daytime photochemistry and in-cloud oxidation. A simple examination of chemical reaction pathways is used to help elucidate the relationships among the sulphur species and oxidants. The relationship between sea salt mass and wind speed is examined. This study marks the first time atmospheric measurements have been included in an iron enrichment experiment, and the first time an Aerodyne Aerosol Mass Spectrometer (AMS) has been deployed in a remote marine setting. Due to the proximity of the ship to the fertilized patch and the relatively high wind speeds, no impact of the SERIES iron fertilization on the local aerosol was observed.

A proton transfer reaction mass spectrometer (PTR-MS) was redesigned and deployed to monitor selected hydrocarbon emissions from in-use vehicles as part of the Mexico City Metropolitan Area (MCMA) 2003 field campaign. This modified PTR-MS instrument provides the necessary time response (

Two Aerodyne AerosolMass Spectrometers (AMS) were depl oyed at three sites representing urban, semi-ruraland rural areas during the Pacific 2001 experiment in the Lower Fraser Valley (LFV), British Columbia, Canada in August 2001. The AMS provides on-line quantitative measurements of the size and chemical composition of the non-refractory fraction of submicron aerosol particles. A significant accumulation mode with a peak around 400–500 nm was observed at all sites that was principally composed of sulphate, organics, ammonium and some nitrate. Another significant mode with a peak below 200 nm was also observed at the urban site and when urban plumes affected the other sites. This paper focuses on the variability of the organic particulate composition and size distribution as a function of location and photochemical activity with a particular emphasis on the urban and rural areas. The small organic mode at the urban site was well correlated with gas phase CO, 1,3-butadiene, benzene and toluene with Pearson’s r values of 0.76, 0.71, 0.79 and 0.69, respectively, suggesting that combustion-related emissions are likely to be the main source of the small organic mode at this site. The mass spectra of the urban organic particulate are similar to those of internal combustion engine lubricating oil, and of diesel exhaust aerosol particles, implying that they were composed of a mixture of n-alkanes, branched alkanes, cycloalkanes, and aromatics. In contrast, organic particulate at the rural site was dominated by shorter chain oxidized organic compounds. Correlations between the two organic modes and gas phase compounds at the ruralsite indicated that a significant part of the smal lmode originated from combustion sources, while the large accumulation organic mode appeared to be the result of photochemical processing. Processing

A generalised method for the deconvolution of mass spectral data from the aerodyne aerosol mass spectrometer (AMS) is presented. In this instrument, the sampled ensemble of gas and non-refractory particle phase materials interfere with each other in the mass spectra and the data must be systematically analyzed to generate meaningful, quantitative and chemically resolved results. The method presented here is designed to arithmetically separate the raw data into partial mass spectra for distinct chemical species. This technique was developed as part of the AMS analysis tools introduced by Allan et al. (J. Geophys. Res. Atmos. 108 (2003) 4090) and is in use by most groups within the AMS users community. This technique employs a user-definable ‘fragmentation table’ for each chemical species or group of species, and examples of some tables designed for the interpretation of field data are given. The ongoing work being performed to develop and validate the tables will be presented in future publications.