Aerodyne Research Research Articles

Atmospheric CH_4 and N_2O measurements near Greater Houston area landfills using a QCL-based QEPAS sensor system during DISCOVER-AQ 2013

A quartz-enhanced photoacoustic absorption spectroscopy (QEPAS)-based gas sensor was developed for methane (CH₄) and nitrous-oxide (N₂O) detection. The QEPAS-based sensor was installed in a mobile laboratory operated by Aerodyne Research, Inc. to perform atmospheric CH₄ and N₂O detection around two urban waste-disposal sites located in the northeastern part of the Greater Houston area, during DISCOVER-AQ, a NASA Earth Venture during September 2013. A continuous wave, thermoelectrically cooled, 158 mW distributed feedback quantum cascade laser emitting at 7.83 μm was used as the excitation source in the QEPAS gas sensor system. Compared to typical ambient atmospheric mixing ratios of CH₄ and N₂O of 1.8 ppmv and 323 ppbv, respectively, significant increases in mixing ratios were observed when the mobile laboratory was circling two waste-disposal sites in Harris County and when waste disposal trucks were encountered.

Schmidt Wins ACS President-Elect

The members of the American Chemical Society have elected Diane Grob Schmidt, a section head at Procter & Gamble, as ACS president-elect for 2014. During her three-year succession, Schmidt will serve as president of the society in 2015 and immediate past-president in 2016; she will also serve on the board of directors during that time. The society, which publishes C&EN, also elected or reelected four other board directors. In the president-elect race, no candidate had a majority of members’ first-choice votes. Because Charles E. Kolb Jr., president and chief executive officer at Aerodyne Research, received the fewest first-choice votes, the second-choice votes of members who preferred Kolb were added to the first-choice votes for G. Bryan Balazs, an associate program leader at Lawrence Livermore National Laboratory, and for Schmidt, per ACS bylaws. That gave Schmidt 42% of the total votes for president-elect, compared with 35% for Balazs and 23% for ...

Candidates Named For ACS Election

Candidates for American Chemical Society president-elect and four additional spots on the ACS Board of Directors have been announced for the society’s fall election. The new president-elect will serve in the society’s three-year presidential succession, and those elected to director seats will serve three-year terms starting in 2014. Candidates for 2014 president-elect are G. Bryan Balazs, associate program leader at Lawrence Livermore National Laboratory; Charles E. Kolb Jr., president and CEO of Aerodyne Research; and Diane Grob Schmidt, R&D section head at Procter & Gamble. Director of District II candidates are George M. Bodner, the Arthur Kelly Distinguished Professor of Chemical Education and an engineering faculty member at Purdue University, and Alan A. Hazari, director of chemistry labs and lecturer at the University of Tennessee, Knoxville. Rigoberto Hernandez, a professor of chemistry at Georgia Institute of Technology, and Larry K. Krannich, a professor emeritus of chemistry at the University ...

Identification of the source of benzene concentrations at Texas City during SHARP using an adjoint neighborhood‐scale transport model and a receptor model

AbstractThe Aerodyne Research Inc. mobile laboratory performed real‐time in‐situ measurements of volatile organic compounds, nitrogen oxides, and formaldehyde in Texas City, Texas on 7 May 2009 during the Formaldehyde and olefins from Large Industrial Releases experiment of the 2009 Study of Houston Atmospheric Radical Precursors (SHARP) campaign. Our goal was to identify and quantify emission sources within the largest industrial facility in Texas City most likely responsible for measured concentrations of benzene, an important VOC and hazardous air pollutant. The Houston Advanced Research Center inverse air quality model has been used to infer benzene emission rates from all potential source locations that could account for the benzene concentrations measured by the mobile lab in the vicinity of the facility. A Positive Matrix Factorization receptor model was also applied to the concentrations measured by the mobile lab, the results of which strongly supported the source attribution specified by the inverse model. The two independent source apportionment techniques both implicated flare, storage tank, and ultraformer units in the facility as significant contributors to emission plumes of elevated benzene concentrations observed by the mobile lab. The emissions of some of the flare and tank units were found to be greater than reported in emission inventories by about an order of magnitude.

Structural analysis of aerosol particles by microscopic observation using a time‐of‐flight secondary ion mass spectrometer

AbstractThe chemical composition and structure of fine aerosol particles with diameters of less than 1 µm were analyzed in the spring of 2011 at Fukue Island, Japan, using an aerosol quadrupole mass spectrometer (Q‐AMS, Aerodyne Research, Inc.) and a time‐of‐flight secondary ion mass spectrometer (TOF‐SIMS). The Q‐AMS results were similar to those of previous studies conducted at the same location, suggesting that the composition we observed is typical of this site. Based on the TOF‐SIMS results, we classified the fine aerosol particles into three types: Type A, in which sulfate was covered with organic matter (OM); Type B, in which soil‐containing particles with a diameter of 0.5 µm were associated with sulfate and OM; and Type C, in which black carbon (BC) and sulfate aggregates were associated with OM. During the observation period, the relative abundances of Type A, B, and C particles were 55%, 20%, and 25%, respectively. The structure, chemical composition, and the proportion of each type of particles provide information for a more representative particle model in radiative models. The relative abundance of Type C, i.e., BC‐containing particles, is quite different to that in Tokyo, suggesting that Type C could be an indicator of transboundary air pollution, in this case from mainland China.

Characterizing the Aging of Biomass Burning Organic Aerosol by Use of Mixing Ratios: A Meta-analysis of Four Regions

Characteristic organic aerosol (OA) emission ratios (ERs) and normalized excess mixing ratios (NEMRs) for biomass burning (BB) events have been calculated from ambient measurements recorded during four field campaigns. Normalized OA mass concentrations measured using Aerodyne Research Inc. quadrupole aerosol mass spectrometers (Q-AMS) reveal a systematic variation in average values between different geographical regions. For each region, a consistent, characteristic ratio is seemingly established when measurements are collated from plumes of all ages and origins. However, there is evidence of strong regional and local-scale variability between separate measurement periods throughout the tropical, subtropical, and boreal environments studied. ERs close to source typically exceed NEMRs in the far-field, despite apparent compositional change and increasing oxidation with age. The absence of any significant downwind mass enhancement suggests no regional net source of secondary organic aerosol (SOA) from atmospheric aging of BB sources, in contrast with the substantial levels of net SOA formation associated with urban sources. A consistent trend of moderately reduced ΔOA/ΔCO ratios with aging indicates a small net loss of OA, likely as a result of the evaporation of organic material from initial fire emissions. Variability in ERs close to source is shown to substantially exceed the magnitude of any changes between fresh and aged OA, emphasizing the importance of fuel and combustion conditions in determining OA loadings from biomass burning.

Pollution Gradients and Chemical Characterization of Particulate Matter from Vehicular Traffic near Major Roadways: Results from the 2009 Queens College Air Quality Study in NYC

We present measurements of traffic-related pollutants made near the Long Island Expressway (LIE, I-495), in Queens, New York. The Aerodyne Research Inc. (ARI) mobile laboratory (AML) was deployed to map spatial and temporal gradients of gas-phase species and particulate matter (PM) associated with vehicular exhaust in the residential areas near the LIE. We observe that pollutant levels build up during the early morning hours under stable boundary layer conditions yet fall off quickly within 150 m downwind of the highway. An ARI soot particle aerosol mass spectrometer (SP-AMS) provided measurements of the size-resolved chemical composition of refractory black carbon (rBC) and the associated coating species. The average size distribution of the traffic related PM is characterized by a rBC mode centered at ∼100 nm in vacuum aerodynamic diameter, D va (rBC mass fraction ∼50%). A second rBC mode (rBC mass fraction ∼5%) more heavily coated with organic material is also observed at D va ∼500 nm. Positive matrix ...

Initial Cooperative Group Experience of Bevacizumab (Bev) Plus Concomitant Chemoradiation Therapy (CRT) in Patients With Inoperable Locally Advanced Stage III Non-small Cell Lung Cancer (LA-NSCLC): Preliminary Results of S0533

Purpose/Objective(s): Radiation pneumonitis (RP) is the most common toxicity following stereotactic ablative radiation therapy (SABR) for lung tumors, but methods to predict which patients will develop this side effect remain lacking. We performed a prospective clinical trial to assess the feasibility and potential of measuring levels of exhaled nitric oxide (NO), carbon monoxide (CO), nitrous oxide (N2O), and carbon dioxide (CO2) as predicative biomarkers of RP in patients receiving SABR to the lung. Materials/Methods: Twenty patients with lung tumors receiving SABR were enrolled in this pilot study. Exhaled concentrations of NO, CO, N2O, and CO2 were simultaneously measured with a real time laser based instrument immediately prior to and following each fraction. Patients were followed for development of symptomatic RP (Grade 2 or higher, CTCAE v4.0). RP incidence was evaluated for correlation with acute changes in exhaled gas concentrations, baseline concentrations, and dosimetric and demographic factors. Results: Five of twenty patients developed RP at an average of 5.4 months following SABR. Average acute changes in NO were 4.10 6.66% (mean standard error) for symptomatic and 33.5 9.31% for asymptomatic patients. Average acute changes in CO were -0.77% 1.53% for symptomatic and -7.32% 1.81% for asymptomatic patients. Average acute change in NO 12.5% and CO -5.5% correlated with RP incidence (p Z 0.036 and p Z 0.035, respectively). Bivariate analysis showed acute change in NO 12.5% combined with acute change in CO -5.5% strongly correlated with RP incidence (p Z 0.003). Baseline NO 24 parts per billion also correlated with RP incidence (p Z 0.036). N2O and CO2 concentrations were not predicative of symptomatic RP. Dosimetric parameters did not predict for the development of RP. Conclusions: Acute changes in exhaled NO and CO concentrations following SABR were found to predict development of RP. Evaluating changes in exhaled NO and CO concentrations immediately following radiation therapy represents a promising method for identifying individuals at highest risk for developing RP. Author Disclosure: J.M. More: None. N.C. Eclov: None. M. Chung: None. J.H. Shorter: A. Employee; JHS is affiliated with Aerodyne Research Inc., which designed the breath analysis instrument used in this study. R. Burmeister: Q. Leadership; RB is affiliated with Kos Systems, which seeks to develop applications for breath analysis. P. Banos: Q. Leadership; PB is affiliated with Kos Systems, which seeks to develop applications for breath analysis. P. Maxim: None. B.W. Loo: None. M. Diehn: None.

Real-Time Measurements of Engine-Out Trace Elements: Application of a Novel Soot Particle Aerosol Mass Spectrometer for Emissions Characterization

Lubricant-derived trace element emissions are the largest contributors to the accumulation of incombustible ash in diesel particulate filters (DPF), eventually leading to filter plugging and an increase in engine fuel consumption. Particulate trace element emissions also pose adverse health effects and are the focus of increasingly stringent air quality regulations. To date, the rates and physical and chemical properties of lubricant-derived additive emissions are not well characterized, largely due to the difficulties associated with conducting the measurements. This work investigated the potential for conducting real-time measurements of lubricant-derived particle emissions. The experiment used the Soot Particle Aerosol Mass Spectrometer (SP-AMS) developed by Aerodyne Research to measure the size, mass and composition of submicron particles in the exhaust. Results confirm the ability of the SP-AMS to measure engine-out emissions of calcium, zinc, magnesium, phosphorous, and sulfur. Further, emissions of previously difficult to detect elements, such as boron, and low-level engine wear metals, such as lead, were also measured. This paper provides an overview of the results obtained with the SP-AMS, and demonstrates the utility of applying real-time techniques to engine-out and tailpipe-out trace element emissions. Application of the SP-AMS for engine exhaust characterization followed a two-part approach: (1) measurement validation, and (2) measurement of engine-out exhaust. Measurement validation utilized a diesel burner with precise control of lubricant consumption. Results showed a good correlation between CJ-4 oil consumption and measured levels of lubricant-derived trace elements in the particle phase. Following measurement validation, the SP-AMS measured engine-out emissions from a medium-duty diesel engine, operated over a standard speed/load matrix. This work demonstrates the utility of state-of-the-art online techniques (such as the SP-AMS) to measure engine-out emissions, including trace species derived from lubricant additives. Results help optimize the combined engine-lubricant-aftertreatment system and provide a real-time characterization of emissions. As regulations become more stringent and emission controls more complex, advanced measurement techniques with high sensitivity and fast time response will become an increasingly important part of engine characterization studies.

Eddy covariance measurements of CO 2 isotopologues with a quantum cascade laser absorption spectrometer

Stable isotope measurements of the biosphere–atmosphere CO 2 exchange can be used to constrain carbon budget estimates on different spatial and temporal scales. Eddy covariance (EC) measurements can provide a direct measure of the isotope flux ratio of CO 2 and thus indicate the ecosystem fingerprint on the isotope budget of the atmosphere. For the first time we report on EC flux measurements of stable CO 2 isotopologues over a forest canopy. We used a quantum cascade laser absorption spectrometer (QCLAS, Aerodyne Research Inc.) for the simultaneous measurement of 12CO 2, 13CO 2 and CO 18O isotopologue fluxes with a sampling rate of 10 Hz over the Lägeren mixed forest site in Switzerland during an intensive field campaign in 2008. The total CO 2 flux measured with the closed-path QCLAS matches well the half-hourly fluxes measured with a conventional open-path infrared gas analyzer ( R 2 = 0.988). The 18O isotope discrimination is strongly reduced after precipitation events, reflecting 18O isotope exchange of CO 2 with water in various water pools of the ecosystem. The 13CO 2/ 12CO 2 flux ratio is surprisingly constant on a diurnal timescale, but the substantial random noise in the half-hourly EC flux ratio puts a limit on resolving diurnal variations of only a few permil. Hence, we explore which component in our EC set-up is limiting the precision of the measured flux ratios. On the one hand we use data simulations to estimate the error contribution from the QCLAS instrument. On the other hand different EC data processing procedures are examined to quantify the uncertainty inherently associated with turbulent flux measurements and calculations. We show that the random error associated with EC data processing is of the same order of magnitude as the flux ratio uncertainty from the instrument precision. Therefore, a direct determination of ecosystem discrimination on hourly or diurnal time scales with the EC technique remains a challenge.

Characterization of Aerosol Particles in the Tokyo Metropolitan Area using Two Different Particle Mass Spectrometers

Particle mass spectrometers of two types—a time-of-flight aerosol mass spectrometer (AMS) of Aerodyne Research Inc. and a laser desorption/ionization single particle aerosol mass spectrometer (LISPA-MS) developed at Nagoya University—were deployed to characterize aerosol particles in the Tokyo metropolitan area during the summer of 2008. Based on the ensemble measurements by AMS, equivalent mass concentration of organic aerosol, traced by mass-to-charge ratio (m/z) 44, showed a closer correlation with particulate nitrate and gas-phase odd oxygen, [O 3 +NO 2 ], whereas equivalent mass concentration of organic aerosol, traced by m/z 57, did not. On a particle-by-particle basis, the relative signal peak area of various target species in the LISPA-MS spectra, which was calculated as the ion-signal fraction of the species relative to the total signal peak area summed over all the ion peaks in each spectrum, was used as a measure of the relative amount of the species. A rough qualitative agreement was obtained ...

Field intercomparison of two optical analyzers for CH<sub>4</sub> eddy covariance flux measurements

Abstract. Fast response optical analyzers based on laser absorption spectroscopy are the preferred tools to measure field-scale mixing ratios and fluxes of a range of trace gases. Several state-of-the-art instruments have become commercially available and are gaining in popularity. This paper aims for a critical field evaluation and intercomparison of two compact, cryogen-free and fast response instruments: a quantum cascade laser based absorption spectrometer from Aerodyne Research, Inc., and an off-axis integrated cavity output spectrometer from Los Gatos Research, Inc. In this paper, both analyzers are characterized with respect to precision, accuracy, response time and also their sensitivity to water vapour. The instruments were tested in a field campaign to assess their behaviour under various meteorological conditions. The instrument's suitability for eddy covariance flux measurements was evaluated by applying an artificial flux of CH4 generated above a managed grassland with otherwise very low methane exchange. This allowed an independent verification of the flux measurements accuracy, including the overall eddy covariance setup and data treatment. The retrieved fluxes were in good agreement with the known artificial emission flux, which is more than satisfactory, given that the analyzers were attached to separate sonic anemometers placed on individual eddy towers with different data acquisition systems but similar data treatment that are specific to the best practice used by the involved research teams.

Characterising aerosol transport into the Canadian High Arctic using aerosol mass spectrometry and Lagrangian modelling

Abstract. We report the analysis of measurements made using an aerosol mass spectrometer (AMS; Aerodyne Research Inc.) that was installed in the Polar Environment Atmospheric Research Laboratory (PEARL) in summer 2006. PEARL is located in the Canadian high Arctic at 610 m above sea level on Ellesmere Island (80° N 86° W). PEARL is unique for its remote location in the Arctic and because most of the time it is situated within the free troposphere. It is, therefore, well suited as a receptor site to study the long-range tropospheric transport of pollutants into the Arctic. Some information about the successful year-round operation of an AMS at a high Arctic site such as PEARL will be reported here, together with design considerations for reliable sampling under harsh low-temperature conditions. Computational fluid dynamics calculations were made to ensure that sample integrity was maintained while sampling air at temperatures that average −40 °C in the winter and can be as low as −55 °C. Selected AMS measurements of aerosol mass concentration, size and chemical composition recorded during the months of August, September and October 2006 will be reported. The air temperature was raised to about 20 °C during sampling, but the short residence time in the inlet system (~25 s) ensured that less than 10% of semivolatiles such as ammonium nitrate were lost. During this period, sulfate was, at most times, the predominant aerosol component with on average 0.115 μg m−3 (detection limit 0.003 μg m−3). The second most abundant component was undifferentiated organic aerosol, with on average 0.11 μg m−3 (detection limit 0.04 μg m−3). The nitrate component, which averaged 0.007 μg m−3, was above its detection limit (0.002 μg m−3), whereas the ammonium ion had an apparent average concentration of 0.02 μg m−3, which was approximately equal to its detection limit. A few episodes, having increased mass concentrations and lasting from several hours to several days, are apparent in the data. These were investigated further using a statistical analysis to determine their common characteristics. High correlations among some of the components arriving during the short-term episodes provide evidence for common sources. Lagrangian methods were also used to identify the source regions for some of the episodes. In all cases, these coincided with the arrival of air that had contacted the surface at latitudes below about 60° N. Most of these lower-latitude footprints were on land, but sulfate emissions from shipping in the Atlantic were also detected. The Lagrangian results demonstrate that there is direct transport of polluted air into the high Arctic (up to 80° N) from latitudes down to 40° N on a time scale of 2–3 weeks. The polluted air originates in a wide variety of industrial, resource extraction and petroleum-related activity as well as from large population centres.

Size dependent partitioning of organic material: evidence for the formation of organic coatings on aqueous aerosols

Organic aerosol formation resulting from the ozonolysis of α-pinene, myrcene and sabinene was investigated in a large aerosol chamber in the presence of aqueous seed aerosols. The chemical composition of the particles was monitored by an aerosol mass spectrometer (Aerodyne Research Inc.) as a function of time and the particle size. Smaller particles were found to contain more organics relative to sulfate than the larger ones. In contrast, the water to sulfate mass ratio was not dependent on the particle size. These experimental findings indicate the formation of organic layers on the particles. With the aid of an aerosol dynamic model we demonstrate that the observations are consistent with the formation of multilayered organic films having thicknesses of approximately 10 nm. The results also suggest that the films were formed through condensation of low-volatile oxidation products that did not take up water considerably. Even though dissolution of oxidation products into the particle aqueous phase cannot be conclusively ruled out, the most plausible interpretation of the results is that the monoterpene ozonolysis lead to the formation of organic coatings on aqueous aerosols. Such films are likely to form in regions with monoterpene emissions.

Chemical and microphysical characterization of ambient aerosols with the aerodyne aerosol mass spectrometer

The application of mass spectrometric techniques to the real-time measurement and characterization of aerosols represents a significant advance in the field of atmospheric science. This review focuses on the aerosol mass spectrometer (AMS), an instrument designed and developed at Aerodyne Research, Inc. (ARI) that is the most widely used thermal vaporization AMS. The AMS uses aerodynamic lens inlet technology together with thermal vaporization and electron-impact mass spectrometry to measure the real-time non-refractory (NR) chemical speciation and mass loading as a function of particle size of fine aerosol particles with aerodynamic diameters between approximately 50 and 1,000 nm. The original AMS utilizes a quadrupole mass spectrometer (Q) with electron impact (EI) ionization and produces ensemble average data of particle properties. Later versions employ time-of-flight (ToF) mass spectrometers and can produce full mass spectral data for single particles. This manuscript presents a detailed discussion of the strengths and limitations of the AMS measurement approach and reviews how the measurements are used to characterize particle properties. Results from selected laboratory experiments and field measurement campaigns are also presented to highlight the different applications of this instrument. Recent instrumental developments, such as the incorporation of softer ionization techniques (vacuum ultraviolet (VUV) photo-ionization, Li+ ion, and electron attachment) and high-resolution ToF mass spectrometers, that yield more detailed information about the organic aerosol component are also described.

Real-Time Measurements of Nitrogen Oxide Emissions from In-Use New York City Transit Buses Using a Chase Vehicle

New diesel engine technologies and alternative fuel engines are being introduced into fleets of mass transit buses to try to meet stricter emission regulations of nitrogen oxides and particulates: Real-time instruments including an Aerodyne Research tunable infrared laser differential absorption spectrometer (TILDAS) were deployed in a mobile laboratory to assess the impact of the implementation of the new technologies on nitrogen oxide emissions in real world driving conditions. Using a "chase" vehicle sampling strategy, the mobile laboratory followed target vehicles, repeatedly sampling their exhaust. Nitrogen oxides from approximately 170 in-use New York City mass transit buses were sampled during the field campaigns. Emissions from conventional diesel buses, diesel buses with continuously regenerating technology (CRT), diesel hybrid electric buses, and compressed natural gas (CNG) buses were compared. The chase vehicle sampling method yields real world emissions that can be included in more realistic emission inventories. The NO, emissions from the diesel and CNG buses were comparable. The hybrid electric buses had approximately one-half the NOx emissions. In CRT diesels, NO2 accounts for about one-third of the NOx emitted in the exhaust, while for non-CRT buses the NO2 fraction is less than 10%.

Floating Solids: Combining Phase Field and Fluid-Structure Interactions

Aerodyne Research, Inc., 45 Manning Road, Billerica. MA 01821-3976 USAReceived 10 May 2004, revised 16 November 2004, accepted 20 November 2004Published online 22 April 2005Key words Phase field, fluid-structure interactions, Navier-Stokes, finite difference.AMS 04A25A mixed-stress formulation presented here combines the methodologies of phase field and fluid-structure inter-actions in order to simulate phase transformations involving moving and rotating solid bodies interacting withfluids. The Navier-Stokes equations are solved everywhere, with an additional strain tensor field overlaid on thesolid, such that elastic stress can be incorporated into the equation of motion. An additional term in the equationfor strain evolution provides rotation due to local vorticity. The results exhibit a small amount of artificial ero-sion of the solid due to nonzero normal velocity within the diffuse interface at separation points; this is discussedhere as a phenomenon common to all diffuse interface formulations incorporating convection. Two-dimensionalsimulations presented here demonstrate oscillations due to feedback between surface tension and elastic stress,and rigid body motion with particle collision and agglomeration which involves a change in the topology of thefluid-solid interface. The formulation and simulations presented here use isotropic Cahn-Hilliard free energy,and extension of the formulation to three-dimensional and anisotropic systems is straightforward. Likewise,these simulations describe linear elastic solids with Poisson ratio of 1 (equivalent to

Measurement of Ambient Aerosol Composition During the PMTACS-NY 2001 Using an Aerosol Mass Spectrometer. Part I: Mass Concentrations Special Issue ofAerosol Science and Technologyon Findings from the Fine Particulate Matter Supersites Program

Semicontinuous ambient aerosol composition measurements performed during the PMTACS-NY Summer 2001 field campaign in Queens/New York with an aerosol mass spectrometer (AMS, developed by Aerodyne Research Inc.) are described. The measurements include 10 min averages of the nonrefractory sulfate, nitrate, ammonium, chloride, and organic mass concentrations in the particle size range of 50 to approximately 1000 nm. Particle-bound water concentrations (i.e., aerosol liquid water content) were estimated from the mass spectral information and local meteorological data. Aggregate semicontinuous AMS mass measurements were compared with those from a TEOM mass monitor that was also deployed at the PMTACS-NY 2001 site. On average, the AMS observed 64% of the total particulate matter mass measured by the TEOM Monitor. Filter and additional semicontinuous particulate sulfate measurements performed simultaneously at the site suggest that the observed discrepancy in mass balance between the two instruments is attributable to a combination of large particles (≥1 μm) lost in the AMS inlet system and the refractory aerosol components not measured by the AMS. Measured diurnal patterns of sulfate, nitrate, organics, and total nonrefractory mass concentrations indicate that elevated PM levels measured during this campaign were due to regional transport as well as local production of particulate matter.

Chase Studies of Particulate Emissions from in-use New York City Vehicles

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 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 CO2 measured simultaneously in the plume. During these studies, nonrefractory PM1.0 (NRPM1) 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 NRPM1/kg fuel to 0.23 g NRPM1/kg, depending on the type of engine used by the bus. The average NRPM1 emission index of diesel-powered buses using Continuously Regenerating Technology (CRT™) trap systems was 0.052 g NRPM1/kg fuel. Buses fueled by compressed natural gas (CNG) had an average emission index of 0.034 g NRPM1/kg Fuel. The mass spectra of the nonrefractory diesel aerosol components measured by the AMS were dominated by lubricating oil spectral signatures. Mass-weighted size distributions of the particles in fresh diesel exhaust plumes peak at vacuum aerodynamic diameters around 90 nm with a typical full width at half maximum of 60 nm.

Analysis of Humidity Halos around Trade Wind Cumulus Clouds

Regions of enhanced humidity in the vicinity of cumulus clouds, so-called cloud halos, reflect features of cloud evolution, exert radiative effects, and may serve as a locus for new particle formation. Reported here are the results of an aircraft sampling campaign carried out near Oahu, Hawaii, from 31 July through 10 August 2001, aimed at characterizing the properties of trade wind cumulus cloud halos. An Aerodyne Research, Inc., fast spectroscopic water vapor sensor, flown for the first time in this campaign, allowed characterization of humidity properties at 10-m spatial resolution. Statistical properties of 60 traverses through cloud halos over the campaign were in general agreement with measurements reported by Perry and Hobbs. One particularly long-lived cloud is analyzed in detail, through both airborne measurement and numerical simulation, to track evolution of the cloud halos over the cloud's lifetime. Results of both observation and the simulation show that cloud halos tend to be broad at lower levels and narrow at upper levels, and broader on the downshear side than on the upshear side, broadening with time particularly in the downshear direction. The high correlation of clear-air turbulence distribution with the halo distribution temporally and spatially suggests that the halo forms, in part, due to turbulent mixing at the cloud boundary. Radiative calculations carried out on the simulated cloud and halo field indicate that the halo radiative effect is largest near cloud top during mature and dissipation stages. The halo-enhanced atmospheric shortwave absorption, averaged over this period, is about 1.3% of total solar absorption in the column.