Aerosol Characteristics and Chemistry
Aerosol properties undergo rapid fluctuations due to changes in meteorological conditions, and contact with other airborne pollutants - influences that vary with time and location. Studies in this area are developing and applying new methodologies to evaluate the chemical and physical characteristics of aerosols, as well as aiming to determine spatiotemporal trends of aerosol sources, size, composition, and concentration. Mechanisms of aerosol formation and transportation are also being examined. An understanding of mechanisms underlying spatiotemporal changes in the physical and chemical characteristics of aerosols is a key link needed to relate aerosol emissions to their environmental and health impacts.
Investigation of on-road Ultrafine and Submicron Particles by combining 1-s Time-Resolution Data obtained from a Fast-Mobility-Particle-Sizer and a Photoacoustic Instrument, X. Yao1, A. J. Knox1, G. J. Evans1, J. R. Brook2, Conference Presentation, CP-WB-2007-07
1Southern Ontario Centre for Atmospheric Aerosol Research, University of Toronto, M5S3E5, Toronto, Ontario, Canada, 2Air Quality Research Division, Environment Canada, M3H5T4, Toronto, CanadaShow Abstract >>
On-road ultrafine (<100 nm) and submicron particles mainly originate from nucleation processes, primary vehicular emissions and background particles. Some freshly nucleated particles in vehicular plumes rapidly grow to large particles via gas-particle condensation and particle-particle coagulation while most nucleated particles evaporate and/or are scavenged by coagulation. These processes occur on the order of seconds or even less than 1-s. Thus, high time-resolution instruments are demanded for studying these rapidly varying particles. The Fast-Mobility-Particle-Sizer and the Photoacoustic Instrument can yield a 1-s particle spectrum and a 1-s BC concentration, respectively. Combining simultaneous measurements made by the two instruments allows for the isolation of the on-road particles freshly emitted and/or formed from background particles and for studying transformation of particles and/or the influence of different vehicle operating conditions on particle concentration and particle size distribution. Two-months of continuous measurements made by the two instruments at a roadside site in Toronto were used to investigate size distributions and transformation of on-road particles. The results show that the two instruments simultaneously detected vehicular emission spikes, which contributed up to 10% of the total particle number concentration and BC concentration in daytime on weekdays. The number and volume size distributions of on-road particles emitted from various engine types operating under different conditions are presented. Bi-modal number size distributions of ultrafine particles with two modes at 9-11 nm and 15-50 nm were frequently detected in spikes. The tri-modal number size distributions with modes at 9-11 nm, 15-50 nm and 60-90 nm were less frequently detected in spikes. The number and volume concentrations normalized by BC concentrations are used to investigate the difference between particle emission characteristics of different engine types. Variations of concentrations and size distributions of on-road particles in spikes are also discussed in terms of the transformation of these particles.
Implications of atmospheric SO2 and aerosol SO42- variability and transport on particle acidity in Toronto, Canada, K. Godri and G.J. Evans, Conference Presentation, CP-WB-2007-06
Southern Ontario Centre for Atmospheric Aerosol Research, University of Toronto, M5S3E5, Toronto, Ontario, CanadaShow Abstract >>
The Ontario Power Generation Nanticoke coal fired power station is of concern to Toronto’s air quality; located ~150km southwest of Toronto, emitted pollutants are regularly transported into the city and observed at the sampling site situated in the downtown core. A four-month sampling campaign conducted during the summer of 2006 semi-continuously measured SO2 and sulphate PM2.5 concentrations using a Dionex Gas Particle Ion Chromatograph with 15 minute intervals. Local and regional sources contribute to the total measured SO2. The geographic origins of regional measured gaseous and particulate species were elucidated using NOAA HYSPLIT Trajectory and Dispersion Model analysis. Local SO2 sources contributed only weakly to total SO2 concentrations: the diurnal fraction of local SO2 concentrations contributed a maximum of 25% to the total from 03:00 to 07:00. Three categories of sulphur episodes were identified: SO2 episodes, haze episodes and simultaneously elevated particle and gas concentrations. The first was characterized by sharp narrow peaks of elevated SO2 levels and low sulphur particulate fractions. Haze episodes were distinguished by low visibility and elevated sulphate particulate concentrations. During the summer 2006 sampling campaign, a total of seven sulphur particulate episodes originating from Nanticoke were identified. However, occasions also existed when air masses traveled over Nanticoke and proceeded into Toronto but no episodes were monitored. Temporal variations in measured sulphate concentrations were examined using meteorological parameters and particle acidity information. The latter parameter was influenced by ammonium and sulphate concentration which dominated the total PM2.5 mass during summer months. Low NH4+/SO42- ratios indicated that the extent of particle neutralization was low. Application of the Aerosol Inorganic Model (AIM-II) to measured data provided in-situ aerosol acidic properties including free H+ concentrations and aerosol pH levels, the latter of which also accounts for the degree of bisulphate ion dissociation. Sulphate particle size was also related to shifts in inorganic aerosol chemical composition and relative humidity. Thermodynamic simulation results were used for understanding the formation pathway and size of these sulphate aerosols.
Examination of seasonal and diurnal variations in water soluble inorganic fine particulate matter and gas precursor emissions in downtown Toronto, Canada,
K. Godri and G.J. Evans, Conference Presentation, CP-WB-2007-05
Southern Ontario Centre for Atmospheric Aerosol Research, University of Toronto, M5S3E5, Toronto, Ontario, CanadaShow Abstract >>
From June 2006 to May 2007, water soluble inorganic aerosols, including Cl-, SO42-, NO3-, NO2- and NH4+, and their associated precursor gas (HCl, SO2, HNO3, HNO2, NH3) concentrations were measured adjacent to a high-traffic street in downtown Toronto, Canada. Semi-continuous measurements averaged over 15 minute intervals were performed with a Dionex Gas Particle Ion Chromatograph. The dataset was analyzed for seasonal and diurnal variation for each pair of inorganic aerosol and its associated precursor gas. Particulate nitrate and HNO3 exhibited a seasonal trend. Local gaseous transport emissions contributed to HNO3 and particulate nitrate production in the winter. Low temperatures and high relative humidity induced gaseous HNO3 and NH3 condensation yielding NH4NO3 aerosol. Consequently, low fractions of total nitrate (TNO3=HNO3+pNO3-) were measured in the gas phase during winter months. Ammonia and particulate ammonium also demonstrate seasonal diurnal differences. During the summer, NH3 correlated with NOx local transport emissions, exhibiting a morning rush hour maxima on weekdays. The progression from summer to winter shifted the morning maxima to an afternoon/evening diurnal peak and the overall magnitude of NH3 concentrations also decreased. Ammonium only demonstrated diurnal variation in the winter when particulate nitrate concentrations are at a maximum. Particulate sulphate and SO2 showed no diurnal variation regardless of season suggesting dominate transport from regional sources throughout the year. The frequency of SO2, and in particular SO42- episodes declined in the winter as did the magnitude of the concentrations measured for each species; less efficient oxidation of SO2 yielded higher winter SO2/SO42- ratios. Toronto’s geographic location allows for low ambient chloride concentrations. However, roadway salting in the winter causes both gas and particulate phase chloride episodes. Early morning chloride particulate peaks were seen daily in the summer and are attributed to the lawn sprinkler system situated close to the sampling inlet. Highly acidic aerosols are associated with the summer months while a shift towards neutralization occurs as the temperature declines.
Characterization of Ultrafine Particles for Use in Exposure Studies, B. Andrew, B.A.Sc. Thesis, BASc-WB-2007-02Show Abstract >>
Ultrafine particles (UFP), particles with a diameter less than 100nm, have been implicated as one of the causative agents of the negative health outcomes of particulate matter. Due to their small size, large surface area to mass ratio, and transient nature, ultrafine particles are difficult to describe in terms of number concentration and size distribution in a way that could be useful for human exposure and other health research. This thesis presents a system for characterizing ultrafine particles in a manner that is simple yet descriptive. The characterization system uses high-resolution data and specific analysis methods to describe UFP characteristics. UFPs were measured near a busy street in downtown Toronto, Ontario, from May 2006 to Janurary 2007. Analysis of the results from the characterization system, gives evidence that this method produces a good representation of UFPs. Additionally, this system showed that the most important parameters for describing the UFP characteristics were the average concentration, the number of spikes per sample, the fraction of monomodal distributions and the distance between size distribution modes. Finally, it was determined that there are four characteristic types of ultrafine particle exposures; extreme, mild, high baseline/low spikes and hybrid exposures.
High Time Resolution of Aerosol Particles in Toronto Using a Gas-Particle Ion
Chromatography System, Krystal Godri and Greg J. Evans, Conference Presentation, CP-WB-2006-02
Department of Chemical Engineering and Applied Chemistry, University of Toronto, M5S 3E5, Toronto, Ontario, CanadaShow Abstract >>
Urban air quality is an area of growing concern. Atmospheric aerosol particles have been linked to poor health by epidemiological studies. (Brook, 2002) It is pertinent to determine the chemical composition, concentrations, size and degree of toxicity of various species of particulate matter (PM). The implementation of a new instrument for the measurement of aerosols and gaseous species is presented in this study. The gas particle ion chromatograph (GP-IC) (Dionex, Al-Horr, 2003) allows for simultaneous concentration collection of PM and atmospheric gas data at a high temporal resolution.
This powerful new monitor utilizes ion chromatography (IC) as an analysis technique. The simplicity and robustness of the GP-IC make it an attractive combined PM and gas species monitor.
This study sampled air collected from downtown Toronto, Ontario, Canada. The sampling location was approximately 20m from a high traffic street surrounded by midsized buildings. The gas-particle ion chromatography instrument drew a total of 10 l/min of air for particulate matter and gaseous analysis. Ion chromatography results were generated with a 15 minute time resolution.
Seasonal trends and episodes as observed from downtown Toronto will be presented. Comparison studies between the GP-IC and other aerosol monitoring instruments will also be discussed.
Al-Horr, R., Samanta, G., and Dasgupta, P.K. (2003) A Continuous Analyzer for Soluble
Anionic Constituents and Ammonium in Atmospheric Particulate Matter, Enviro. Sci. Technol., 37, 5711-5720.
Brook, R.D., Brook, J.R., Urch, B., Vincent, R., Rajagopalan, S., Silverman, F. (2002)
Inhalation of fine particulate air pollution and ozone cause acute arterial vasoconstriction in healthy adults.Circulation, 105, 1534-4536.
Application of MAX-DOAS to Canadian Urban and Rural Sites, R. J. C. D’Souza1, G. J. Evans1 and J. R. Brook2, Conference Presentation,
1Department of Chemical Engineering, University of Toronto, 200 College St., M5S3E5, Toronto, Canada, 2Air Quality Research Division, Environment Canada, 4905 Dufferin St., M3H5T4, Toronto, CanadaShow Abstract >>
Air pollutants affecting tropospheric air quality can vary in concentration with altitude as well as in two dimensions across a region. Differential Optical Absorption Spectroscopy (DOAS) is a relatively new approach to help derive multi-dimensional tropospheric urban concentrations of trace pollutant gases from ground-based UV-visible measurements. Column amounts of absorbers, in particular, nitrogen dioxide, formaldehyde and aerosols, can be obtained. The MAX-DOAS instrument consists of a small telescope that collects scattered sunlight. This light is fed to a commercial miniature Czerny-Turner Spectrograph/Detector Unit (Ocean Optics USB2000) covering a wavelength range from 290-440 nm, within which SO2, NO2, and HCHO absorb strongly. Spectra are collected at small elevation angles with the intention of discerning nuanced vertical trace gas variations within the troposphere, in particular, the boundary layer. The MAX-DOAS study intends to demonstrate the capability of the technique to derive column amounts of different trace gases and information on their vertical location in both rural and urban regions within Canada. Monitoring was performing in August 2005 as part of the Canadian Regional and Urban Investigation System for Environmental Research (CRUISER) campaign at a rural location SE of Edmonton, and in 2006 at downtown Toronto, York, Burlington and Center Island. Radiative transfer modelling is used to validate results obtained and to provide further information on diurnal mixing height variation and the vertical aerosol extinction profile.
Analysis of Air Pollutants using MAX-DOAS, S. Basma, Summer Research Report, SRA-WB-2006-01Show Abstract >>
Multi Axis Differential Optical Absorption Spectroscopy (MAX DOAS) is a new approach to derive atmospheric column densities, and possibly, the concentrations of trace gases such as O4, NO2,and formaldehyde. MAX DOAS uses scattered sunlight received from different viewing angles to provide a distribution of pollutants in the atmosphere. Measurements using MAX DOAS were taken at various locationsin the GTA during the summer of 2006. The effect of viewing geometry on O4 measurements was examined, along with the relationship between O4 abundance and aerosol load. Decent correlations were found between O4 measurements and particulate matter concentrations.The slant column densities of O4 were observed to decrease with increasing PM2.5 concentration. This trend was especially prominent at low elevation angles. The changes in O4 measurements were also used as an indication of the path length variation. A relative ratio of NO2 to O4 differential slant column density was calculated and used as an estimation of the NO2 concentration. Results were compared to data obtained from the NOx analyzer, and showed some variability.