Organic aerosol (OA) particles affect climate forcing and human health, but their sources and evolution remain poorly characterized. We present a unifying model framework describing the atmospheric evolution of OA that is constrained by high-time-resolution measurements of its composition, volatility, and oxidation state. OA and OA precursor gases evolve by becoming increasingly oxidized, less volatile, and more hygroscopic, leading to the formation of oxygenated organic aerosol (OOA), with concentrations comparable to those of sulfate aerosol throughout the Northern Hemisphere. Our model framework captures the dynamic aging behavior observed in both the atmosphere and laboratory: It can serve as a basis for improving parameterizations in regional and global models.

Organic aerosol (OA) data acquired by the Aerosol Mass Spectrometer (AMS) in 37 field campaigns were deconvolved into hydrocarbon‐like OA (HOA) and several types of oxygenated OA (OOA) components. HOA has been linked to primary combustion emissions (mainly from fossil fuel) and other primary sources such as meat cooking. OOA is ubiquitous in various atmospheric environments, on average accounting for 64%, 83% and 95% of the total OA in urban, urban downwind, and rural/remote sites, respectively. A case study analysis of a rural site shows that the OOA concentration is much greater than the advected HOA, indicating that HOA oxidation is not an important source of OOA, and that OOA increases are mainly due to SOA. Most global models lack an explicit representation of SOA which may lead to significant biases in the magnitude, spatial and temporal distributions of OA, and in aerosol hygroscopic properties.

We report the development and first field deployment of a new version of the Aerosol Mass Spectrometer (AMS), which is capable of measuring non-refractory aerosol mass concentrations, chemically speciated mass distributions and single particle information. The instrument was constructed by interfacing the well-characterized Aerodyne AMS vacuum system, particle focusing, sizing, and evaporation/ionization components, with a compact TOFWERK orthogonal acceleration reflectron time-of-flight mass spectrometer. In this time-of-flight aerosol mass spectrometer (TOF-AMS) aerosol particles are focused by an aerodynamic lens assembly as a narrow beam into the vacuum chamber. Non- Although the research described in this article has been funded in part by the U.S. EPA, it has not been subjected to the Agency's peer and policy review and therefore does not necessarily reflect the views of the Agency, and no official endorsement should be inferred. We thank Phil Mortimer from Aerodyne Research, Inc., James Schwab from ASRC at SUNY Albany, and Queens College for logistical support during the PMTACS campaign. S. Hings thanks International Max Planck Research School for funding for her participation in this work. J.L. Jimenez and P. DeCarlo thank the U.S. Dept. of Energy (DE-FG02-03ER83599) and the Office of Naval Research (grant N00244-04-P-0425) for funding participation in this work.Address correspondence to Frank Drewnick, Max Planck Institute for Chemistry, Cloud Physics and Chemistry Department, J. J. Becherweg 27, D-55128 Mainz, Germany. E-mail: drewnick@ mpch-mainz.mpg.de refractory particle components flash-vaporize after impaction onto the vaporizer and are ionized by electron impact. The ions are continuously guided into the source region of the time-of-flight mass spectrometer, where ions are extracted into the TOF section at a repetition rate of 83.3 kHz. Each extraction generates a complete mass spectrum, which is processed by a fast (sampling rate 1 Gs/s) data acquisition board and a PC. Particle size information is obtained by chopping the particle beam followed by time-resolved detection of the particle evaporation events. Due to the capability of the time-of-flight mass spectrometer of measuring complete mass spectra for every extraction, complete single particle mass spectra can be collected. This mode provides quantitative information on single particle composition. The TOF-AMS allows a direct measurement of internal and external mixture of non-refractory particle components as well as sensitive ensemble average particle composition and chemically resolved size distribution measurements. Here we describe for the first time the TOF-AMS and its operation as well as results from its first field deployment during the PM 2.5 Technology Assessment and Characterization Study-New York (PMTACS-NY) Winter Intensive in January 2004 in Queens, New York. These results show the capability of the TOF-AMS to measure quantitative aerosol composition and chemically resolved size distributions of the ambient aerosol. In additi...

Submicron aerosol particles (PM₁) were measured in-situ using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer during the summer 2009 Field Intensive Study at Queens College in New York, NY. Organic aerosol (OA) and sulfate are the two dominant species, accounting for 54% and 24%, respectively, of the total PM₁ mass. The average mass-based size distribution of OA presents a small mode peaking at ~150 nm (<i>D</i>_va) and an accumulation mode (~550 nm) that is internally mixed with sulfate, nitrate, and ammonium. The diurnal cycles of both sulfate and OA peak between 01:00–02:00 p.m. EST due to photochemical production. The average (±σ) oxygen-to-carbon (O/C), hydrogen-to-carbon (H/C), and nitrogen-to-carbon (N/C) ratios of OA in NYC are 0.36 (±0.09), 1.49 (±0.08), and 0.012 (±0.005), respectively, corresponding to an average organic mass-to-carbon (OM/OC) ratio of 1.62 (±0.11). Positive matrix factorization (PMF) of the high resolution mass spectra identified two primary OA (POA) sources, traffic and cooking, and three secondary OA (SOA) components including a highly oxidized, regional low-volatility oxygenated OA (LV-OOA; O/C = 0.63), a less oxidized, semi-volatile SV-OOA (O/C = 0.38) and a unique nitrogen-enriched OA (NOA; N/C = 0.053) characterized with prominent C_xH_{2x + 2}N⁺ peaks likely from amino compounds. Our results indicate that cooking and traffic are two distinct and mass-equivalent POA sources in NYC, together contributing ~30% of the total OA mass during this study. The OA composition is dominated by secondary species, especially during high PM events. SV-OOA and LV-OOA on average account for 34% and 30%, respectively, of the total OA mass. The chemical evolution of SOA in NYC appears to progress with a continuous oxidation from SV-OOA to LV-OOA, which is further supported by a gradual increase of O/C ratio and a simultaneous decrease of H/C ratio in total OOA. Detailed analysis of NOA (5.8% of OA) presents evidence that organic nitrogen species such as amines might have played an important role in the atmospheric processing of OA in NYC, likely involving both acid-base chemistry and photochemistry. In addition, analysis of air mass trajectories and satellite imagery of aerosol optical depth (AOD) indicates that the high potential source regions of secondary sulfate and aged OA are mainly located in regions to the west and southwest of the city

Emissions from motor vehicles are a significant source of fine particulate matter (PM) and gaseous pollutants in urban environments. Few studies have characterized both gaseous and PM emissions from individual in-use vehicles under real-world driving conditions. Here we describe chase vehicle studies in which Received 27 February 2003; accepted 29 March 2004. This work was supported in part by the New York State Energy Research and Development Authority (NYSERDA), contract # 4918ERT-ERES99; the US Environmental Protection Agency (EPA), cooperative agreement # R828060010; and New York State Department of Environmental Conservation (NYS DEC), contract # C004210. Although the research described in this article has been funded in part by US EPA, it has not been subjected to the Agency's required peer and policy review and therefore does not necessary reflect the views of the Agency, and no official endorsement should be inferred. The authors thank the MTA for their cooperation, including Chris Bush for providing bus fleet information and Dana Lowell for help in organizing the logistics of the Fall 2000 campaign, the NYS DEC for providing drivers during the chase experiments, and Queens College for logistical support during the Summer 2001 campaign. The TILDAS scientists on-board the mobile laboratory, particularly Joanne Shorter and Mark Zahniser, are acknowledged for their assistance throughout the two phases of this study. Thanks also go to Jay Slowik and Leah Williams for help with laboratory soot experiments, Tim Onasch for assistance with the development of data analysis programs, and Paul Ziemann for useful discussions about organic mass spectral analysis. P. J. Silva thanks the Camille and Henry Dreyfus Foundation for Support. D. A. Ghertner thanks Robert Harriss for providing funding for his involvement in this project.Address correspondence to Manjula R. Canagaratna, Center for Aerosol and Cloud Chemistry and Center for Atmospheric and Environmental Chemistry, Aerodyne Research Inc., 45 Manning Road, Billerica, MA 01821, USA. E-mail: mrcana@aerodyne.com on-road emissions from individual vehicles were measured in real time within seconds of their emission. This work uses an Aerodyne aerosol mass spectrometer (AMS) to provide size-resolved and chemically resolved characterization of the nonrefractory portion of the emitted PM; refractory materials such as elemental carbon (EC) were not measured in this study. The AMS, together with other gas-phase and particle instrumentation, was deployed on the Aerodyne Research Inc. (ARI) mobile laboratory, which was used to "chase" the target vehicles. Tailpipe emission indices of the targeted vehicles were obtained by referencing the measured nonrefractory particulate mass loading to the instantaneous CO 2 measured simultaneously in the plume. During these studies, nonrefractory PM 1.0 (NRPM 1 ) emission indices for a representative fraction of the New York City Metropolitan Transit Authority (MTA) bus fleet were determined. Diesel bus emissions ranged from 0.10 g NRPM 1...

In a companion paper (Kroll, J. H.; Clarke, J. S.; Donahue, N. M.; Anderson, J. G.; Demerjian, K. L. J. Phys. Chem. A 2001, 105, 1554) we present direct measurements of hydroxyl radical (OH) yields for the gas-phase reaction of ozone with a number of symmetric alkenes. Yields are strongly pressure-dependent, contrary to the results of prior scavenger studies. Here we present a statistical-dynamical model of OH production from the reaction, utilizing RRKM/master equation calculations to determine the fate of the carbonyl oxide intermediate. This model agrees with our experimental results, in that both theory and observations indicate strongly pressure-dependent OH yields. Our calculations also suggest that ethene ozonolysis produces OH via a different channel than the substituted alkenes, though the identity of this channel is not clear. This channel may play a role in the ozonolysis of monosubstituted alkenes as well. Our time-dependent master equation calculations show that the discrepancy between OH yields measured in our direct study and those measured in prior scavenger studies may arise from differing experimental time scales; on short time scales, OH is formed only from the vibrationally excited carbonyl oxide intermediate, whereas on longer time scales OH formation from thermal dissociation may be significant. To demonstrate this we present time-dependent measurements of OH yields at 10 Torr and 100 Torr; yields begin increasing after hundreds of milliseconds, an effect which is much more pronounced at 100 Torr. These results are entirely consistent with theoretical predictions. In the atmosphere, the thermalized carbonyl oxide may be susceptible to bimolecular reactions which, if fast enough, could prevent dissociation to OH; however there is little experimental evidence that any such reactions are important. Thus we conclude that both mechanisms of OH formation (dissociation of vibrationally excited carbonyl oxide and dissociation of thermalized carbonyl oxide) are significant in the troposphere.

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During the summer of 1988, measurements of photochemical trace species were made at a coordinated network of seven rural sites in the eastern United States and Canada. At six of these sites concurrent measurements of ozone and the sum of the reactive nitrogen species, NOy, were made, and at four of the sites a measure for the reaction products of the NO x oxidation was obtained. Common to all sites, ozone, in photochemically aged air during the summer, shows an increase with increasing NOy levels, from a background value of 30-40 parts per billion by volume (ppbv)at NOy mixing ratios below 1 ppbv to values between 70 to 100 ppbv at NOy levels of 10 ppbv. Ozone correlates even more closely with the products of the NOx oxidation. The correlations from the different sites agree closely at mixing ratios of the oxidation products below 5 ppbv, but systematic differences appear at higher levels. Variations in the biogenic hydrocarbon emissions may explain these differences. IntroductionElevated and potentially harmful levels of ozone are being found in many rural areas of North America during summer. Daily maximum 03 levels measured in rural areas are often comparable to those found in urban areas and daily average levels can exceed urban levels. There is substantial evidence from field measurements and model calculations that most of this ozone is being produced photochemically from ozone precursors emitted within the region [Research Triangle Institute, 1975; Vukovich et al., 1977Vukovich et al., , 1985Cleveland et al., 1977;Spicer et al., 1979;Wolff and Lioy, 1980;Fehsenfeld et al., 1983;Kelly et al., 1984;Liu et al., 1987]. A similar situation appears to exist for western Europe [Cox et al., 1975;Guicherit and Van Dop, 1977;Hov, 1984]. The photochemical processes responsible for these high levels are thought to be quite similar to the processes that operate in urban photochemical smog but with important differences. In