J. G. Murphy

University of Toronto, Toronto, Ontario, Canada

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Publications (40)65.44 Total impact

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    ABSTRACT: Tropospheric ozone (O3) is a major component of photochemical smog and is a known human health hazard as well as a damaging factor for vegetation. Its precursor compounds, nitrogen oxides (NOx) and volatile organic compounds (VOCs), have a variety of anthropogenic and biogenic sources and exhibit non-linear effects on ozone production. As an update to previous studies on ground-level ozone in the GTA, we present an analysis of NO2, VOC and O3 data from federal and provincial governmental monitoring sites in the GTA from 2000-2012. We show that over the study period, summertime 24 h VOC reactivity and NO2 midday (11:00-15:00) concentrations at all sites decreased significantly; since 2000, all sites experienced a decrease in NO2 of 28-62% and in measured VOC reactivity of at least 53-71%. Comparing 2002/2003 to 2011/2012, the summed reactivity of OH towards NO2 and a suite of measured VOCs decreased from 8.6 to 4.6 s-1. Ratios of reactive VOC pairs indicate that the effective OH concentration experienced by primary pollutants in the GTA has increased significantly over the study period. Despite the continuous decrease in precursor levels, ozone concentrations are not following the same pattern at all stations; it was found that the Canada-Wide Standard for ozone continues to be exceeded at all monitoring stations. Additionally, while the years 2008-2011 had consistently lower ozone levels than previous years, 2012 experienced one of the highest recorded summertime ozone concentrations and a large number of smog episodes. We demonstrate that these high ozone observations in 2012 may be a result of the number of days with high solar radiation, the number of stagnant periods and the transport of high ozone levels from upwind regions.
    03/2014; 14(7).
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    J. A. Geddes, J. G. Murphy
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    ABSTRACT: Significant knowledge gaps persist in the understanding of forest-atmosphere exchange of reactive nitrogen oxides, partly due to a lack of direct observations. Chemical transport models require representations of dry deposition over a variety of land surface types, and the role of canopy exchange of NOx (= NO + NO2) is highly uncertain. Biosphere-atmosphere exchange of NOx and NOy (= NOx + HNO3 + PANs + RONO2 + pNO3- + ...) was measured by eddy covariance above a mixed hardwood forest in central Ontario (HFWR), and a mixed hardwood forest in northern lower Michigan (PROPHET) during the summers of 2011 and 2012 respectively. NOx and NOy mixing ratios were measured by a custom built two-channel analyzer based on chemiluminescence, with selective NO2 conversion via LED photolysis and NOy conversion via a hot molybdenum converter. Consideration of interferences from water and O3, and random uncertainty of the calculated fluxes are discussed. NOy flux observations were predominantly of deposition at both locations. The magnitude of deposition scaled with NOy mixing ratios, resulting in campaign-average deposition velocities close to 0.6 cm s-1 at both locations. A~period of highly polluted conditions (NOy concentrations up to 18 ppb) showed distinctly different flux characteristics than the rest of the campaign. Integrated daily average NOy flux was 0.14 mg (N) m-2 day-1 and 0.34 mg (N) m-2 day-1 at HFWR and PROPHET respectively. Concurrent wet deposition measurements were used to estimate the contributions of dry deposition to total reactive nitrogen oxide inputs, found to be 22% and 40% at HFWR and PROPHET, respectively.
    Atmospheric Chemistry and Physics 10/2013; 13(10):27891-27936. · 4.88 Impact Factor
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    Biogeosciences 01/2013; 10:4371. · 3.75 Impact Factor
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    ABSTRACT: Methane flux measurements were carried out at a temperate forest (Haliburton Forest and Wildlife Reserve) in central Ontario (45°17´11´´ N, 78°32´19´´ W) from June-October, 2011. Continuous measurements were made by an off-axis integrated cavity output spectrometer Fast Greenhouse Gas Analyzer (FGGA) from Los Gatos Research Inc. that measures methane (CH4) at 10 Hz sampling rates. Fluxes were calculated from the gas measurements in conjunction with wind data collected by a 3-D sonic anemometer using the eddy covariance (EC) method. Observed methane fluxes showed net uptake of CH4 over the measurement period with an average uptake flux (± standard deviation of the mean) of -2.7 ± 0.13 nmol m-2 s-1. Methane fluxes showed a seasonal progression with average rates of uptake increasing from June through September and remaining high in October. This pattern was consistent with a decreasing trend in soil moisture content at the monthly time scale. On the diurnal timescale, there was evidence of increased uptake during the day, when the mid-canopy wind speed was at a maximum. These patterns suggest that substrate supply of CH4 and oxygen to methanotrophs, and in certain cases hypoxic soil conditions supporting methanogenesis in low-slope areas, drive the observed variability in fluxes. A network of soil static chambers used at the tower site showed close agreement with the eddy covariance flux measurements. This suggests that soil-level microbial processes, and not abiological leaf-level CH4 production, drive overall CH4 dynamics in temperate forest ecosystems such as Haliburton Forest.
    Biogeosciences Discussions 12/2012; 9(12):17743-17774.
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    ABSTRACT: Two methods based on ion chromatography (IC) were developed for the detection of methyl and ethyl alkyl amines (methylamine (MA), ethylamine (EA), dimethylamine (DMA), diethylamine (DEA), trimethylamine (TMA) and triethylamine (TEA)) and NH(3)/NH(4)(+) in online atmospheric gas-particle and size-resolved particulate samples. The two IC methods were developed to analyze samples collected with an ambient ion monitor (AIM), an online gas-particle collection system, or with a Micro Orifice Uniform Deposit Impactor (MOUDI) for size-resolved particle samples. These methods enable selective and (semi-) quantitative detection of alkyl amines at ambient atmospheric concentrations (pptv and pgm(-3)) in samples where significant interferences can be expected from Na(+) and NH(4)(+), for example marine and rural air masses. Sample pre-concentration using a trace cation column enabled instrumental detection limits on the order of pmol (sub-ng) levels per sample, an improvement of up to 10(2) over current IC methods. Separation was achieved using a methanesulfonic acid gradient elution on Dionex CS12A and CS17 columns. The relative standard deviations in retention times during 3 weeks continuous (hourly) sampling campaigns ranged from 0.1 to 0.5% and 0.2 to 5% for the CS12A and CS17 across a wide dynamic range of atmospheric concentrations. Resolution of inorganic and organic cations is limited to 25min for online samples. Mass-dependent coelution of NH(4)(+)/MA/EA occurred on the CS12A column and DEA/TMA coeluted on both columns. Calibrations of ammonium show a non-linear response across the entire calibration range while all other analytes exhibit high linearity (R(2)=0.984-0.999), except for EA and TEA on the CS12A (R(2)=0.960 and 0.941, respectively). Both methods have high analytical accuracy for the nitrogenous bases ranging from 9.5 to 20% for NH(3) and <5-15% for the amines. Hourly observations of amines at Egbert, ON in October 2010 showed gaseous DMA and TMA+DEA at 1-10pptv in air, while particulate DMA and TMA+DEA were present at 0.5-4ng m(-3). A size-resolved particulate sample collected over 23h was found to contain DMA, TMA+DEA and MEA at 1.78, 8.15 and 0.03ngm(-3) mass loadings, with the amine mass enhanced in particle sizes between 100 and 1000nm. These results highlight a need for very sensitive and selective detection of methyl and ethyl amines in addition to NH(3) in continuous online monitoring strategies.
    Journal of Chromatography A 06/2012; 1252:74-83. · 4.61 Impact Factor
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    ABSTRACT: Gas and fine particle (PM2.5) phase formic acid concentrations were measured with online instrumentation during separate one-month studies in the summer of 2010 in Los Angeles (LA), CA, and Atlanta, GA. In both urban environments, median gas phase concentrations were on the order of a few ppbv (LA 1.6 ppbv, Atlanta 2.3 ppbv) and median particle phase concentrations were approximately tens of ng/m3 (LA 49 ng/m3, Atlanta 39 ng/m3). LA formic acid gas and particle concentrations had consistent temporal patterns; both peaked in the early afternoon and generally followed the trends in photochemical secondary gases. Atlanta diurnal trends were more irregular, but the mean diurnal profile had similar afternoon peaks in both gas and particle concentrations, suggesting a photochemical source in both cities. LA formic acid particle/gas (p/g) ratios ranged between 0.01 and 12%, with a median of 1.3%. No clear evidence that LA formic acid preferentially partitioned to particle water was observed, except on three overcast periods of suppressed photochemical activity. Application of Henry's Law to predict partitioning during these periods greatly under-predicted particle phase formate concentrations based on bulk aerosol liquid water content (LWC) and pH estimated from thermodynamic models. In contrast to LA, formic acid partitioning in Atlanta appeared to be more consistently associated with elevated relative humidity (i.e., aerosol LWC), although p/g ratios were somewhat lower, ranging from 0.20 to 5.8%, with a median of 0.8%. Differences in formic acid gas absorbing phase preferences between these two cities are consistent with that of bulk water-soluble organic carbon reported in a companion paper.
    Journal of Geophysical Research 01/2012; 117:D00V21. · 3.17 Impact Factor
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    ABSTRACT: In May-July 2010, the Calnex field study was conducted by National Oceanic and Atmospheric Administration (NOAA), California Air Resources Board (CARB), and other partners to answer important scientific questions about emissions, chemical transformations, climate processes, transport, and meteorology in California. The study provided a rich dataset of observations from aircrafts, ships, and supersites, which were supplemented by California's routine monitoring networks. For the CalNex period, CARB and US EPA conducted high-resolution three-dimensional air-quality simulations of gas and particle pollutants over California using different modeling platforms based on the Community Multiscale Air Quality (CMAQ) model. Simulated concentrations of different species from the two modeling systems were directly compared to measurements from routine ground monitoring networks as well as observations from different field study platforms. This investigation aims to improve the understanding of the physical and chemical processes that control the formation of air pollutants in California and to provide insight on the capabilities, development needs, and differences of the modeling systems used by CARB and US EPA.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: Nitryl chloride formation from reaction of N2O5 on chloride-containing aerosol has proven to be a widespread phenomenon in the polluted troposphere. Understanding this process involves some of the most challenging aspects of gas and particle phase chemistry, and interfacial transport. For example, it is useful to consider how well we understand related issues such as: N2O5 uptake, particle chloride chemistry, and the ultimate effect of this chlorine atom source on the photochemistry. In addition, the high levels of nitryl chloride that are produced in this chemistry present the possibility that further chlorine activation chemistry could be happening on particles. This talk will attempt to summarize where we are in understanding the myriad aspects of this interesting chemistry, and possible additional processes.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: To investigate formation of secondary organic aerosol (SOA) and the contribution of SOA to organic aerosols, semi-volatile and intermediate-volatile organic compounds (SVOCs/IVOCs) in both gas and particle phases were measured using a modified Thermal Desorption Gas Chromatograph (TAG) instrument in Bakersfield, CA during the CALifornia at the NEXus between air quality and climate (CALNEX) campaign from 31 May through 27 June, 2010. More than 150 organic compounds were identified, spanning a wide range of volatility and functionality. Quantified compounds included organic tracers for primary and secondary organic sources, such as alkanes, PAHs, acids, hopanes and ketones. Hourly gas/particle partitioning was determined by a denuder difference method where the sample flow alternated every other sample through an active charcoal multi-channel denuder that efficiently removed gas-phase components. Gas/particle partitioning of three SOA tracers (phthalic acid, pinonaldehyde and 6, 10, 14-trimethyl-2-pentadecanone) was investigated to understand the formation mechanisms of SOA for different functional group classes in the ambient atmosphere. Comparison with Pankow gas/particle partitioning theory, observed particle-phase phthalic acid and pinonaldehyde, suggests formation by other mechanisms than gas-to-particle condensation. Source attribution is performed using Positive Matrix Factorization (PMF) analysis of speciated particle-phase TAG data along with total submicron organic aerosol (OA) measured by an Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS). SOA accounts for a major component of OA and the contribution of biogenic SOA to total SOA is comparable to anthropogenic SOA during nights.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: There is extensive evidence that ultrafine particles (Dp<100 nm) have adverse effects on human health. In this study, physical and chemical properties of ultrafine aerosol particles are investigated at a polluted urban site in Bakersfield, California. The analysis is based on measurements during the CalNex campaign 15 May to 29 June in 2010. Aerosol measurements in this study include mainly particle number size distributions provided by a Scanning Mobility Particle Sizer (SMPS) and size resolved aerosol chemical composition determined with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS). Growth events of ultrafine particles were observed on most days during the campaign and the events had a very regular pattern. A nucleation mode centered at 10-20 nm appeared in early morning and was observed to grow up to 40-100 nm throughout the day. Most of the growth events were regional, representing horizontal scales of at least 100 km. Microphysical modeling and size-resolved HR-ToF-AMS concentrations show that organic components dominated the particle growth in the ultrafine mode, and sulfate provided only a minor contribution to the growth. The ultrafine mass was largely dominated by organics (83%) and was in general at maximum during the afternoon, indicating the importance of photochemistry. Whereas elemental carbon and the AMS tracer m/z 57 for hydrocarbon-like organic aerosol (HOA) peaked in early morning during rush hour, indicative of primary emissions, particle number concentration peaked in the afternoon. This is interpreted as a result of new particle formation. Potentially important parameters for both growth and new particle formation, as concentrations of oxidizers and different organic and inorganic vapors, have been investigated.
    Journal of Geophysical Research 12/2011; · 3.17 Impact Factor
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    ABSTRACT: The pH of atmospheric particles is considered an important property that plays a role in gas-particle partitioning of many atmospheric constituents, the aqueous phase processing of organics, and the health effects of particle exposure. It is challenging to measure aerosol pH directly, but it is possible to combine measurements of particle composition, relative humidity and temperature with calculations from aerosol thermodynamics algorithms to calculate the bulk pH. While this approach is relatively straightforward in environments with high levels of strong acidity (> 20 neq m-3), it produces a high level of uncertainty (> 6 pH units) in more neutral conditions. We demonstrate that simultaneous measurements of gas phase NH3 offer a powerful additional constraint that can reduce the calculated pH uncertainty by an order of magnitude. This approach is used to calculate aerosol pH in several rural and urban environments including measurements from Bakersfield and Pasadena during CalNex 2010. We explore the validity of the assumptions of gas-particle equilibrium partitioning and internal mixing of particles, as well as the impact of organic acids and bases.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: The 2010 California Research at the Nexus of Air Quality and Climate Change (CalNex) field campaign supersite in Bakersfield, CA, presented an opportunity to investigate the gas-particle partitioning of trace atmospheric species in a low-sulphur high-NH3 environment. With the demand for cleaner energy, atmospheric S levels are expected to continue to decrease across North America, while restrictions on NH3 emissions are still in preliminary stages. Despite the absence of significant sulphur emissions contributing to particulate matter (PM) formation, California's San Joaquin Valley still experiences some of the worst air quality in the continental US. Partitioning of other trace gases may become more important in low sulphur regions; here we report our observations of HONO, HCl and oxalic acid partitioning. Observations of the water-soluble composition of atmospheric gases and fine particulate matter (PM2.5) were made with an Ambient Ion Monitor - Ion Chromatography (AIM-IC) system from University Research Glassware (Chapel Hill, NC). The AIM-IC was fitted with a newly designed impactor inlet that minimizes gas and particle losses prior to collection by a wet wall parallel plate denuder and super saturated steam condensation chamber, respectively, situated at a height of 4.5 m for this study. Observations of NH3 indicated ambient levels typically in excess of 10 ppb, up to 60 ppb, and all observed inorganic aerosol was found to be completely neutralized throughout the campaign by NH4+. Mixing ratios of HONO showed excellent agreement with concurrent measurements made by a LOPAP instrument from University of Miami, maximizing during the night at values in the range of 1 - 1.5 ppb. On several nights, particulate NO2- mass loadings in the range of 0.2 mug m-3 (equivalent to 0.1 ppb HONO) were observed by the AIM-IC. The diurnal pattern of HCl showed maximum mixing ratios of 0.2 - 0.3 ppb occurring near 13:00 PST, and near zero values at night. Intermittent bursts of Cl- were also detected, however the Cl- present in PM2.5 was significantly less than that present as HCl. These online observations are some of the few to date describing simultaneous measurements of both gas and particle phase reservoirs of chlorine as HCl/Cl-. The diurnal pattern of oxalic acid showed maximum mixing ratios less than 0.1 ppb near 16:00 PST and near zero values at night. The presence of oxalate in PM2.5 was observed throughout the campaign with mass loadings in the range of 0 - 0.2 mug m-3 also maximizing during the day.
    AGU Fall Meeting Abstracts. 12/2010;
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    ABSTRACT: During the 2010 California Nexus between Air Quality and Climate Change (CalNex) study, we utilized a modified Ambient Ion Monitor Ion Chromatograph (AIM-IC) to monitor PM2.5 and gas composition at Bakersfield, CA supersite. AIM-IC is an instrument capable of simultaneous measurements of soluble PM2.5 composition (dominated by NH4+, SO42-, NO3-) and associated precursor gases (NH3(g), SO2(g), HNO3(g)) on a nearly continuous basis with a time resolution of 1 hour. We describe a novel inlet design that enabled the instrument to acquire tower-height measurements from the base of the tower with minimal inlet losses. In this configuration gases and particles were stripped into solution in the tower-mounted assembly, minimizing sampling losses for NH3 and HNO3. The inlet assembly consisted of an aluminum box equipped with 2.5 µm impactor positioned on the Teflon®-coated aluminum tube, a wet parallel-plate denuder, and particle super saturation chamber. Electrical and liquid sample lines (~ 20 m in length) were connected to the main body of the instrument which was located in a trailer at the base of the tower. Among the PM2.5 constituents, we found NH4NO3 to be the most dominant species by mass. In addition, NH4NO3 exhibited a large concentration maximum in the morning and a smaller one in the late afternoon. Significant levels of (NH4)2SO4 were observed in the late afternoon only, most likely due to regional air transport. In terms of aerosol acidity, we observed a fully neutralized aerosol throughout the study. NH3 was the dominant soluble gas phase species as a consequence of large agricultural emissions in San Joaquin Valley. HNO3 displayed a diurnal maximum around noon as a result of gas/particle partitioning of volatile NH4NO3 and possibly from local photochemical production. We detected, on-average, sub-ppb levels of SO2, consistent with the absence of major SO2 emission sources in the region. In this work, we also examine meteorological and chemical factors that affected the gas/particle partitioning of the NH4+- SO42-- NO3- system in this region that is characterized by warm weather, very high NH3 and low SO42- precursor emissions.
    AGU Fall Meeting Abstracts. 12/2010;
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    ABSTRACT: The CalNex 2010 field campaign aimed to study atmospheric processes impacting air quality and climate change in California from ground, airborne and ship platforms. At the CalNex-LA ground site, measurements of gas phase ammonia (NH3), nitric acid (HNO3), hydrochloric acid (HCl) and particulate ammonium, nitrate, sulphate and chloride were obtained. Gas phase NH3 was measured by quantum cascade tunable infrared laser differential absorption spectroscopy (QC-TILDAS), HNO3 and HCl by chemical ionization mass spectrometry (CIMS) and the chemical composition of particles was measured by aerosol mass spectrometry (AMS) and Particle-into-Liquid Sampling (PILS) with ion chromatography detection. Mixing ratios of ammonia ranged between 1 and 6 ppb, with higher values during the day. The diurnal profile of NH3 closely follows that of HNO3, both of which peak in concentration around noon. The diurnal profile of particle ammonium is not as pronounced because it follows both particle nitrate, which peaks in the morning, and particle sulfate, which peaks in the afternoon. There was always sufficient ammonia present to fully neutralize particle sulfate, but the equilibrium product for ammonium nitrate formation was only exceeded under certain meteorological conditions. Preliminary analysis using the E-AIM aerosol thermodynamics model suggests aerosol to be in thermodynamic equilibrium with gas phase NH3. Using this uniquely complete dataset, we can fully investigate inorganic gas-particle partitioning and estimate aerosol pH.
    AGU Fall Meeting Abstracts. 12/2010;
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    ABSTRACT: Peroxyacetyl nitrate (PAN) and its chemical analogues are increasingly being quantified in the ambient atmosphere by thermal dissociation (TD) followed by detection of either the peroxyacyl radical or the NO<sub>2</sub> product. Here we present details of the technique developed at University of California, Berkeley which detects the sum of all peroxynitrates (ΣPNs) via laser-induced fluorescence (LIF) of the NO<sub>2</sub> product. We review the various deployments and compare the Berkeley ΣPNs measurements with the sums of PAN and its homologue species detected individually by other instruments. The observed TD-LIF ΣPNs usually agree to within 10% with the summed individual species, thus arguing against the presence of significant concentrations of unmeasured PAN-type compounds in the atmosphere, as suggested by some photochemical mechanisms. Examples of poorer agreement are attributed to a sampling inlet design that is shown to be inappropriate for high NO<sub>x</sub> conditions. Interferences to the TD-LIF measurements are described along with strategies to minimize their effects.
    Atmospheric Measurement Techniques. 01/2010;
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    ABSTRACT: The Border Air Quality and Meteorology Study (BAQS-Met) was an intensive, collaborative field campaign during the summer of 2007 that investigated the effects of transboundary pollution, local pollution, and local meteorology on regional air quality in Southwestern Ontario. This analysis focuses on the measurements of the inorganic constituents of particulate matter with diameter of less than 1 μm (PM1), with a specific emphasis on nitrate. We evaluate the ability of AURAMS, the Environment Canada&apos;s chemical transport model, to represent regional air pollution in SW Ontario by comparing modelled aerosol inorganic chemical composition with measurements from Aerosol Mass Spectrometers (AMS) onboard the National Research Council (NRC) of Canada Twin Otter aircraft and at a ground site in Harrow, ON. The agreement between modelled and measured pNO3− at the ground site (observed mean (M_obs) = 0.50 μg m−3; modelled mean (M_mod) = 0.58 μg m−3; root mean square error (RSME) = 1.27 μg m−3) was better than aloft (M_obs = 0.32 μg m−3; M_mod = 0.09 μg m−3; RSME = 0.48 μg m−3). Possible reasons for discrepancies include errors in (i) emission inventories, (ii) atmospheric chemistry, (iii) predicted meteorological parameters, or (iv) gas/particle thermodynamics in the model framework. Using the inorganic thermodynamics model, ISORROPIA, in an offline mode, we find that the assumption of thermodynamic equilibrium is consistent with observations of gas and particle composition at Harrow. We develop a framework to assess the sensitivity of PM1 nitrate to meteorological and chemical parameters and find that errors in both the predictions of relative humidity and free ammonia (FA ≡ NH3(g) + NH4+ − SO42−) are responsible for the poor agreement between modelled and measured values.
    Atmospheric Chemistry and Physics 01/2010; · 4.88 Impact Factor
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    ABSTRACT: An ion chromatographic method is described for the quantification of the simple alkyl amines: methylamine (MA), dimethylamine (DMA), trimethylamine (TMA), ethylamine (EA), diethylamine (DEA) and triethylamine (TEA), in the ambient atmosphere. Limits of detection (3σ) are in the tens of pmol range for all of these amines, and good resolution is achieved for all compounds except for TMA and DEA. The technique was applied to the analysis of time-integrated samples collected using a micro-orifice uniform deposition impactor (MOUDI) with ten stages for size resolution of particles with aerodynamic diameters between 56 nm and 18 μm. In eight samples from urban and rural continental airmasses, the mass loading of amines consistently maximized on the stage corresponding to particles with aerodynamic diameters between 320 and 560 nm. The molar ratio of amines to ammonium (R3NH+/NH4+) in fine aerosol ranged between 0.005 and 0.2, and maximized for the smallest particle sizes. The size-dependence of the R3NH+/NH4+ ratio indicates differences in the relative importance of the processes leading to the incorporation of amines and ammonia into secondary particles. The technique was also used to make simultaneous hourly online measurements of amines in the gas phase and in fine particulate matter using an Ambient Ion Monitor Ion Chromatograph (AIM-IC). During a ten day campaign in downtown Toronto, DMA, TMA+DEA, and TEA were observed to range from below detection limit to 2.7 ppt in the gas phase. In the particle phase, MAH+ and TMAH++DEAH+ were observed to range from below detection limit up to 15 ng m−3. The presence of detectable levels of amines in the particle phase corresponded to periods with higher relative humidity and higher mass loadings of nitrate. While the hourly measurements made using the AIM-IC provide data that can be used the evaluate the application of gas-particle partitioning models to amines, the strong size-dependence of the R3NH+/NH4+ ratio indicates that using bulk measurements and an assumption of internal mixing may not be appropriate.
    Atmospheric Chemistry and Physics 01/2010; · 4.88 Impact Factor
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    ABSTRACT: The Border Air Quality and Meteorology study (BAQS-Met) was an intensive field campaign conducted in Southwestern Ontario during the summer of 2007. The focus of BAQS-Met was determining the causes of the formation of ozone and fine particulate matter (PM2.5), and of the regional significance of trans-boundary transport and lake breeze circulations on that formation. Fast (1 Hz) measurements of ammonia were acquired using a Quantum Cascade Laser Tunable Infrared Differential Absorption Spectrometer (QC-TILDAS) at the Harrow supersite. Measurements of PM2.5 ammonium, sulfate and nitrate were made using an Ambient Ion Monitor Ion Chromatograph (AIM-IC) with hourly time resolution.The median mixing ratio of ammonia was 2.5 ppb, with occasional high spikes at night resulting from local emissions. Measurements were used to assess major local emissions of NH3, diurnal profiles and gas-particle partitioning. The measurements were compared with results from A Unified Regional Air-quality Modelling System (AURAMS). While the fraction of total ammonia (NHx≡NH3 + NH4+) observed in the gas phase peaks between 0.1 and 0.8, AURAMS tended to predict fractions of either less than 0.05 or greater than 0.8. The model frequently predicted acidic aerosol, in contrast withobservations whereinNHx always exceeded the observed equivalents of sulfate. One explanation for our observations is that the net flux of ammonia from the land surface to the atmosphere increases when aerosol sulfate is present, effectively buffering the mixing ratio of gas phase ammonia, a process not included in the model. We explore the impact of a bi-directional flux parameterization on the predicted gas-particle partitioning of atmospheric ammonia.
    Atmospheric Chemistry and Physics 01/2010; · 4.88 Impact Factor
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    ABSTRACT: The UC Berkeley TD-LIF technique detects the sum of all peroxynitrates (PNs) via laser-induced fluorescence (LIF) of NO2 produced by the by thermal dissociation (TD) of peroxyacetyl nitrate (PAN) and its chemical analogues. We review the various deployments and compare the Berkeley PNs measurements with the sums of PAN and PAN-type species detected individually by other instruments. The observed PNs usually agree to within 10% with the summed individual species, thus arguing against the presence of significant concentrations of unmeasured PAN-type compounds in the atmosphere as suggested by some photochemical mechanisms. Interferences to the TD-LIF measurements are described along with strategies to minimize their effects.
    AGU Fall Meeting Abstracts. 12/2009;
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    ABSTRACT: Characterizing area-source volatilization of ammonia has presented many challenges using fast-response techniques such as eddy covariance due to the adhesive and reactive nature of NH3 within the measuring system. A series of laboratory experiments were conducted to determine the optimal setup using a tunable diode laser absorption spectrometer (TDLAS). The series of experiments were performed concomitantly between the TDLAS and a quantum cascade tunable infrared laser differential absorption spectrometer and results are presented in a companion paper. These experiments consisted of a range of standard additions (10-1000ppbv) using both perfluoroalkoxy (PFA) and polyethylene (PE) inlet tubing ranging in lengths between 3.9 and 8.9m. To address the issue of NH3 adsorption, a test using a heated (40oC) 5-m PE sample line was used in one test series. The standard NH3 additions were mixed with either pre-purified N2 or ambient room air to mimic ambient field conditions. A novel sample inlet, provided by University of Toronto and based on the design of Aerodyne Inc., was employed for the test duration. This inlet was designed to relinquish the use of a filter on the inlet, which may pose attenuation and sample flow issues. The responses to concentration changes using these various configurations demonstrated that the response to the [NH3] changes exhibited a double exponential decay. On average, the primary decay curve represented 88% of the total change in concentration and the average decay coefficient was 0.24s. However, the secondary decay coefficient was much larger (35.2s). The optimal response of the TDLAS was obtained using the shortest length of PFA tubing (3.9m) where the primary decay responses were all greater than 90% of the total change in 0.17s on average and the remaining decay occurred over a period of 0.12s. Surprisingly, the test using the heated PE tubing did not produce any discernible improvements to the instrument response. The optimal configuration proved to be a viable setup of the instrumentation for measuring NH3 fluxes over agricultural landscapes.
    AGU Spring Meeting Abstracts. 05/2009;

Publication Stats

227 Citations
65.44 Total Impact Points

Institutions

  • 2010–2014
    • University of Toronto
      • Department of Chemistry
      Toronto, Ontario, Canada
  • 2005–2006
    • California Institute of Technology
      Pasadena, California, United States
  • 2004–2006
    • University of California, Berkeley
      • Department of Chemistry
      Berkeley, CA, United States