Kevin Bruce Strawbridge

The physical and chemical evolution of aerosols in smelter and power plant plumes: an airborne study

National and international concern about the health effects and continued use of Pb, Cd, As and Hg as well as other metals has defined a need for improved estimates of the long-term risks to ecosystems and human health from metals released from mining, metallurgical and energy production activities. A research aircraft was used to determine the microphysical and chemical properties of airborne particulate metal emissions from the Nanticoke coal-fired power-generating station located on the north shore of Lake Erie, Ontario, and the Horne copper smelter at Rouyn-Noranda, Quebec. These properties are critical to the determination of the deposition rates of the metals emitted, and hence the potential for these species to have impacts on local or distant ecosystems. An overview of the measurements made during the study is given. The size distributions of particles emitted from the stacks and observed within 5 km of the point of emission are briefly described. After dilution by ambient air, the concentration of particles smaller than 0.135 μm in diameter in the plumes is tens of thousands per cubic centimetre, far exceeding the concentrations found in ambient air. However, in the size range 0.135 to 3 μm diameter the plumes generally contribute about one to four times more particles than present in ambient air.

Turbulent heat fluxes over leads and polynyas, and their effects on arctic clouds during FIRE.ACE: Aircraft observations for April 1998

Abstract In this study, aircraft observations obtained during the First International Satellite Cloud Climatology Project @ISCCP) Regional Experiment‐Arctic Cloud Experiment (FIRE.ACE) were used to calculate latent and sensible heat fluxes over leads and polynyas. The purpose of this study is to analyse turbulent heat fluxes related to ocean surface characteristics, and study their effect on Arctic cloud formation. Aircraft passes were made over the leads and polynyas at an altitude of about 100 m. The measurements of a Land Resources Satellite System (LANDSAT) simulator, an airborne PRT‐5 infra‐red radiometer, and a lidar at 1.064 μm wavelength were used to specify ocean surface characteristics. Air temperature, vertical air velocity, and water vapour density measurements were used in the flux calculations. Cloud microphysical parameters, e.g., droplet concentration, ice crystal concentration, and water content were obtained using optical and hot wire probes. The results indicated that a 3‐km lead generated a sensible heat flux of 56 W m−2 and a latent heat flux of 14 W m−2, whereas over the ice they were about ‐20 W m−2 and ‐13 W m−2, respectively. Turbulent fluxes from leads and polynyas were found to be highly variable because of various surface and environmental conditions. Temperature at the ocean water surface reached 3°C on 8 April 1998 and this high surface temperature could also be related to steam fog or thin cloud. Clouds tended to form over the leads and polynyas or in the downwind region as cold air moved from north to south, resulting in a temperature difference of 15°–20°C. The effective radius and droplet concentrations were calculated to be less than 8 μm and 90 cm−3, respectively, in such clouds. The effective values were found to be significantly less than those (∼10 μm) of mid‐latitude clouds over the ocean.

Aerosol backscattering determined from chemical and physical properties and lidar observations over the east coast of Canada

In August to September 1995 a field experiment was conducted over the Gulf of Maine and Bay of Fundy to study the radiative forcing of pollution aerosols. The chemical and physical characteristics of two pollution cases were studied in detail in contrast to a clean atmosphere case. In the pollution cases, NH4++SO4= showed a unimodal distribution with a peak at 0.24 µm diameter. It was dominant among identified chemical components, including inorganic ions and organic compounds. However, the identified components were only about 1/3 of the aerosol mass as determined from the physical measurements. The unidentified mass, with a large accumulation mode, was likely due to unmeasured organic matter. In the clean case, sea salt was the dominant species with a bimodal distribution. The results were used to calculate the direct backscatter coefficient βπ at 0.532 and 1.064 µm using the Mie theory for comparison with LIDAR observations to determine the contributions by the chemical components. In the clean case, the sea salt aerosols contributed about half of βπ. In the pollution cases, NH4++SO4=contributed 20–40% to βπ. The unidentified mass had contributions to βπ of >40% and >70% for the two pollution cases. The LIDAR βπ results were inverted to derive optical depths over the 300–2400 m altitude range. Using these optical depths, the direct backscattered fraction of radiative flux for the pollution aerosols was estimated to be about 5 times higher than aerosols in the clean atmosphere.

Scanning lidar: a means of characterizing the Noranda-Hornesmelter plume

The Meteorological Service of Canada has recently developed a mobile scanning lidar facility (RASCAL: Rapid Acquisition SCanning Aerosol Lidar) capable of fast azimuth and elevation scanning profiles of the lower troposphere. Lidar is a remote sensing technique that provides high temporal and spatial information on atmospheric particulates and was ideally suited for characterizing stack plume dynamics. RASCAL was located predominantly downwind of the Noranda-Horne smelter stack source located in northern Quebec. Two three-week periods during February (winter) and July/August (summer) of 2000 were chosen to examine the behaviour of the plume because of the differences in humidity and boundary layer dynamics. The scanning speeds were adjusted to allow a complete scanning profile to be collected within 30–60 seconds. Along-plume-axis and cross-sectional scans provided an opportunity to directly measure plume dynamics and interaction with the planetary boundary layer, including the ability to detect fumigation events. Several algorithms have been developed to quantify the area, shape, horizontal and vertical extents of the plume as a function of the distance from source. Examples are shown where the cross-sectional area of the plume remained constant at a given distance from source even though its shape was highly variable. Also, boundary layer height, wind speed and direction of the plume can be extracted from the RASCAL data under certain conditions. These data are valuable for comparison with model predictions as well as providing initialization input for long range dispersion models.

Numerical Simulations of Stratus Clouds and Their Sensitivity to Radiation— A RACE Case Study

The three-dimensional Canadian Mesoscale Compressible Community model has been run at high resolution (Dx 5 2 km, Dz 5 50 m) to simulate stratus clouds observed on 1 September 1995 during the Radiation, Aerosol and Cloud Experiment (RACE) conducted near the Bay of Fundy, Canada. A new explicit cloud scheme and the Canadian operational radiation scheme were validated at this resolution for the first time. The simulations show a reasonable agreement between the observed and modeled stratus cloud system. The cloud structure, position, cloud water content, temperature, and the qualitative properties of longwave and shortwave radiative fluxes were verified against the satellite imagery, lidar, and aircraft measurements taken during RACE. The simulated cloud thickness (;150 m) was thinner than the observed one (200‐250 m). The differences in the simulated and observed radiative fluxes were mainly due to errors in the simulation of cloud thickness. Sensitivity experiments demonstrate that the simulated cloud is extremely sensitive to longwave and shortwave radiation. Longwave (shortwave) radiation substantially increased (decreased) the total water path.

Application of Lidar Data to Assist Airmass Discrimination at the Whistler Mountaintop Observatory

AbstractA ground-based lidar system that has been deployed in Whistler, British Columbia, Canada, since the spring of 2010 provides a means of evaluating vertical aerosol structure in a mountainous environment. This information is used to help to determine when an air chemistry observatory atop Whistler Mountain (2182 m MSL) is within the free troposphere or is influenced by the valley-based planetary boundary layer (PBL). Three case studies are presented in which 1-day time series images of backscatter data from the lidar are analyzed along with concurrent meteorological and air-chemistry datasets from the mountaintop site. The cases were selected to illustrate different scenarios of diurnal PBL evolution that are expected to be common during their respective seasons. The lidar images corroborate assumptions about PBL influence as derived from analysis of diurnal trends in water vapor, condensation nuclei, and ozone. Use of all of these datasets together bolsters efforts to determine which atmospheric la...

Preliminary Analysis of Night‐time Aerosol Optical Depth Retrievals at a Rural, Near‐urban Site in Southern Canada

In the summer of 2007, a SPSTAR03 starphotometer was installed at Egbert, Canada (44°13′ N, 79°45′ W, alt 264 m) and a continuous series of initial measurements was performed between August 26 and September 19. Several sunphotometry parameters such as the aerosol optical depth (AOD) and the “fine” and “coarse” optical depths were extracted from the SPSTAR03 extinction spectra. The SPSTAR03 data was analyzed in conjunction with sunphotometry and zenith‐pointing lidar data acquired during the same time period. Preliminary results show coarse continuity between the day‐ and night time AOD values (with the mean difference between the measured and the interpolated values being 0.05) as well as a qualitative correlation between the “fine” and “coarse” optical depths and the normalized lidar backscatter coefficient profiles. It was also found that the spectra produced with the differential two‐star measurement method were sensitive to non‐horizontally homogeneous differences in the line‐of‐sight conditions of bo...

Continuous 1064/532 nm Lidar Measurements (CORALNet-UBC) in Vancouver, British Columbia: Selected Results from a Year of Operation

CORALNet-UBC was installed in April 2008 as a “proof of concept” and the first facility in a proposed cross-Canada network of similar lidars. Despite its location on the wet West Coast of Canada, data recovery ranged from a low of 45% of the total time in December, when heavy snowfall interrupted operations, to a high of 90% in July. The facility has been a spectacular success in terms of its operational characteristics (as measured by data recovery), the range of phenomena observed and the research that it has spawned. Examples are provided of the types of phenomena observed since its initial deployment. These include observations of boundary layer structure, cloud signatures, forest fire plumes and evidence of singular long-range pollutant and volcanic transport events. Observations from CORALNet-UBC complement data from other aerosol measurement initiatives in the region and provide a rich source of information that is relevant to researchers, operational forecasters and air quality managers. Future research will be directed at elucidating the processes and phenomena revealed by the instrument as well as developing new products that exploit the real-time forecasting and public advisory potential of the facility.

High Resolution Nested Runs of the AURAMS Model with Comparisons to PrAIRie2005 Field Study Data

The PrAIRie2005 campaign took place in the summer of 2005 in the city of Edmonton, Alberta. The measurement campaign was designed and led by air-quality modellers with the scientific objective of determining the extent to which air pollution events in the city are the result of locally emissions versus long-range transport. A nested version of the AURAMS model was constructed for post-campaign simulations and evaluation against the measurement data. The nested model runs at different resolutions, the highest of which is a 3 km horizontal resolution centered on the urban area.

Preliminary results from scanning lidar measurements of stack plumes during winter/summer

Results from scanning lidar measurements obtained during a large field study entitled Physical and Chemical Evolution of Aerosols in Smelter and Power Plant Plumes will be presented. The Meteorological Service of Canada has recently developed a mobile scanning lidar facility capable of fast azimuth and elevation scanning profiles of the lower troposphere. The lidar was located downwind of the stack source and the scanning speeds were adjusted to allow a complete scanning profile to be collected within 30-60 seconds. The lidar portion of the study was divided into four three- week parts. Ontario Power Generation-Nanticoke is a coal- fired generating station on the shores of Lake Erie. The lidar ground location selected for both the summer and winter study was approximately 8.5 km east of the stacks. The other location was the Noranda-Horne Smelter in Northern Quebec. The lidar was located approximately 4.6 km SE of the smelter during the winter and approximately 2.5 km NNE during the summer study. Preliminary lidar results will be shown for both Nanticoke and Noranda with a focus on the differences between winter and summer periods when the humidity and boundary layer dynamics were very different. New algorithms are being developed to extract boundary layer heights and plume heights for comparison with model predictions.