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Rehbein P.J.G.,RWDI AIR Inc. | Lepage M.F.,RWDI AIR Inc. | Cotsman D.J.,RWDI AIR Inc. | Gauthier M.,RWDI AIR Inc. | Tandalam A.,RWDI AIR Inc.
Proceedings of the Air and Waste Management Association's Annual Conference and Exhibition, AWMA | Year: 2015

The mixing height is a very important parameter in effecting modelled concentrations from tall stacks. Based on modelling, highest concentrations occur when the mixing height is just above the height of the stack, however the average concentrations can peak at higher mixing heights. Monitoring data does not capture the maximum concentrations occurring right when the mixing height is at the height of the stack, likely because the mixing height is a very difficult parameter to accurately predict. The monitored data does, however, show similar average trends to what is predicted by the model.

Seguin A.M.,University of Calgary | Seguin A.M.,RWDI AIR Inc. | Norman A.-L.,University of Calgary | Barrie L.,University of Stockholm
Journal of Geophysical Research: Atmospheres | Year: 2014

The influence of frost flowers and seawater brine on ion chemistry in snow, snowpack, ice cores, and aerosols is detected when a lower sulfate to sodium ratio than in seawater is present in polar regions. This evidence can be masked when large amounts of non-sea-salt sulfate are present from other sources such as biogenic and anthropogenic sulfate. Frost flower δ34S values were measured for the first time in frost flower sulfates and did not differ significantly from the sea salt δ34S values of +21‰. A method using stable isotopes is introduced to determine the limit of contributions from sea salt and sea ice sources (including frost flowers and brine) on sulfate concentrations in aerosol samples from Alert, Canada. Knowledge of the range of values of δ34Snss and the SO4/Na ratio found in sea ice sources (i.e., frost flowers) is used to quantitatively constrain the contributions from frost flowers and sea salt in the Arctic aerosol mass during the onset of winter in 2007 and 2008, allowing for quantification of non-sea-salt sulfate amounts during times when frost flowers are present. Frost flower and/or brine influence was found predominantly in the coarse-mode aerosols (>0.95 μm). This method to determine the contributions from sea salt and sea ice sources can be carried over to future studies with snow and ice cores. Key Points Frost flower δ34S values measured for the first time Apportionment of frost flower, sea salt and NSS sulfate in Arctic aerosols Frost flower quantification for size segregated aerosols at Alert ©2014. American Geophysical Union. All Rights Reserved.

Roy J.,RWDI Air Inc. | Lewis R.,RWDI Air Inc.
INTER-NOISE 2015 - 44th International Congress and Exposition on Noise Control Engineering | Year: 2015

Best practice guidelines from the American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) Handbook call for mounting generators with a concrete inertia base for installations above grade; however, in the authors' experience generators are often installed without such bases. Also, in our experience, there is a common perception amongst building owners that when they are used such isolation bases will reduce the steady-state vibration forces transmitted to a building structure. In this paper we compare vibration isolation with and without a concrete inertia base for several common structure types and discuss practical limitations for the implementation of inertia bases. Challenges often include accommodating the extra weight and height of an inertial base. © 2015 by ASME.

Kennedy M.G.,RWDI AIR Inc. | Lewis R.,RWDI AIR Inc.
Air and Waste Management Association - Greenhouse Gas Strategies in a Changing Climate Conference 2011 | Year: 2011

In the Canadian context, the province of Alberta has led the way in terms of developing and implementing GHG reporting, management and verification policy. Debate around the effectiveness of this policy aside, the province's relatively early action and efforts to pioneer untested policy have made it a leader in this area. Over the course of three compliance cycles, there have been important lessons learned by all parties involved in Alberta's GHG program including regulators, industry and verifiers. The regulations, associated guidance documentation and communication channels will continue to evolve with improving clarity, fairness and effectiveness. Industry is growing accustomed to the regulatory requirements; is investing in well-trained staff and emissions data collection, management and reporting systems; and is including GHG emissions management in its operational and capital budgets, in some cases to make reductions at the source. Finally, through training and certification exercises, verifiers are becoming well-versed in the theory and concepts of third party GHG verification as laid out in authoritative sources such as ISO 14064-3, and are applying these concepts with greater effectiveness. Hopefully the lessons learned in Alberta will be helpful to those jurisdictions about to embark on their own programs with their own verification requirements.

Reuten C.,RWDI AIR Inc. | Reuten C.,University of British Columbia | Ainslie B.,University of British Columbia | Steyn D.G.,University of British Columbia | And 3 more authors.
Atmosphere - Ocean | Year: 2012

Assuming current emissions and background concentrations, we investigate how changes in synoptic meteorology alone affect ozone episodes in the Lower Fraser Valley, Canada, in future climates. We perform synoptic typing of combined sea level pressure and 500 hPa geopotential heights for June to September 1961- 2000 using the National Centers for Environmental Prediction (NCEP) reanalysis data. Five clusters provide a qualitatively good representation of typical synoptic conditions and stratify exceedance days into one cluster with more than half of all exceedances. Independent cluster analyses for climate model output from the Third Generation Coupled Global Climate Model (CGCM3.1 T63) 1961-2000 control runs and 2046-65 Special Report on Emissions Scenarios (SRES) A1B scenario runs give clusters qualitatively similar to those using NCEP data. When CGCM output is mapped to the NCEP clusters, the CGCM control run cluster frequencies are almost identical to NCEP frequencies, while CGCM 2046-65 output shows only small frequency changes. This indicates that, in future climates, the frequency of occurrence of synoptic types conducive to ozone exceedances will not be appreciably different than they are in the present climate. However, the CGCM predicts substantial increases in daily maximum temperatures in the Lower Fraser Valley across all five clusters. An analysis of exceedance probabilities suggests that the predicted temperature increase will more than double the number of exceedance days per year.

Arthurs D.,RWDI AIR Inc. | Ziada S.,McMaster University
Experiments in Fluids | Year: 2014

This article experimentally investigates the self-excited impinging planar jet flow, specifically the development and propagation of large-scale coherent flow structures convecting between the nozzle lip and the downstream impingement surface. The investigation uses phase-locked particle image velocimetry measurements and a new structure-tracking scheme to measure convection velocity and characterize the impingement mechanism near the plate, in order to develop a new feedback model that can be used to predict the oscillation frequency as a function of flow velocity (Uo), impingement distance (xo) and nozzle thickness (h). The resulting model prediction shows a good agreement with experimental tone frequency data. © 2014 Springer-Verlag Berlin Heidelberg.

Arthurs D.,RWDI AIR Inc. | Bolduc M.,JHE 316 | Ritcey A.,JHE 316 | Ziada S.,JHE 316
International Journal of Aeroacoustics | Year: 2014

The phenomenon of flow-excited acoustic resonance, where periodic flow oscillations are enhanced by a resonant sound field, is a design concern in many engineering applications such as in heat exchangers, piping systems, and cavity flows. This study experimentally examines the phenomenon of flow-excited acoustic resonance for two side-by-side cylinders in a duct with cross-flow. This geometry has been investigated for three cylinder spacing ratios, defined as the center-to-center distance between the cylinders normalized by their diameter, of T/D =1.25, 1.46 and 2.5, and for a range of acoustic pressure amplitudes. Intermediate and small spacing ratios have been given special attention, as these cases have been found to exhibit bistable flow in the wake in the absence of acoustic resonance. Phase-locked PIV measurements reveal that the self-excited sound field produces a strong oscillatory flow pattern in the cylinder wakes, which is symmetric for large spacing ratios and high acoustic amplitudes, but remains bistable for small spacing ratios, even during very intense acoustic resonances. The aeroacoustic sources and sinks within the flow field, computed using Howe's theory of vortex sound, are compared for the range of spacing ratios and acoustic pressure amplitudes examined in this study.

Ainslie B.,University of British Columbia | Ainslie B.,Environment Canada | Steyn D.G.,University of British Columbia | Steyn D.G.,African Institute for Mathematical Sciences | And 3 more authors.
Atmosphere - Ocean | Year: 2013

A mechanistic exploration of how ozone formation in the Lower Fraser Valley (LFV) has changed over a 20-year (1985-2005) retrospective period was performed using numerical models, observations, and emissions data from four key episodes selected from the 20-year period. The motivation for this study was the observed differences in trends in summertime episodic ozone concentrations recorded at various monitoring stations within the valley; stations in the western part of the valley have generally shown a noticeable reduction in episodic ozone concentrations whereas stations in the eastern part of the valley have shown little or no improvement in their maximum 8-hour averaged ozone concentrations. Concurrent with these air quality changes, there has been a well-documented reduction in ozone precursor emissions along with an observed shift in the population patterns within the valley over the 20-year period. Ozone formation for four episodes, encompassing the different meteorological regimes that occur during LFV ozone events and spanning the retrospective period, were investigated using the Weather Research and Forecasting (WRF)-Sparse Matrix Operator Kernel Emission (SMOKE)-Community Multiscale Air Quality (CMAQ) modelling system. For each episode, two simulations, intended to isolate the effects of emission changes from meteorological changes, were performed: one with emissions set at the 1985 level and the other with emissions set at the 2005 level. Based on analysis of the model output, observational data, and precursor emission inventories, we find that the Port Moody station in the western LFV remains a volatile organic compound (VOC)-sensitive location; the central part of the LFV around the town of Chilliwack has generally changed from being VOC-limited to being NOx-limited; the easternmost part of the valley around the town of Hope has been and remains NOx-limited. Furthermore, based on the observational data and numerical model output, ozone production efficiency as a function of NO has increased noticeably at Chilliwack and likely in the other eastern parts of the valley. This efficiency increase has likely offset some of the benefits resulting from local NOx emission reductions.

Steyn D.G.,University of British Columbia | Steyn D.G.,African Institute for Mathematical Sciences | Ainslie B.,University of British Columbia | Reuten C.,University of British Columbia | And 2 more authors.
Atmosphere - Ocean | Year: 2013

We conduct a retrospective study of ozone formation in the Lower Fraser Valley (LFV), using numerical models, observations, and emission inventories in order to understand relationships between reductions in local precursor emissions and episodic ozone concentrations. Because there appears to be little or no impact from precursor emissions upwind of the LFV during ozone episodes and because background concentrations of ozone and its precursors are generally from the North Pacific Ocean and quite low, summertime ozone formation in the LFV is mostly caused by local emissions. The observed change in behaviour of ozone formation must, therefore, arise from reductions in local precursor emissions. We exploit the observed changing precursor emission- ozone concentration relationship to perform a dynamical model evaluation. Complicating the analyses are an observed shift in the population patterns within the valley over the last 25 years and a small but documented change in the tropospheric background concentration of ozone. Ozone formation for four episodes, which capture the observed changes in ozone reduction and the different meteorological types that occur during LFV ozone events, are investigated using the Weather Research and Forecasting (WRF)-Sparse Matrix Operator Kernel Emissions (SMOKE)-Community Multiscale Air Quality (CMAQ) modelling system. In order to provide realistic simulations of past events, the SMOKE emission inventory is adjusted to account for temporal changes in the amount of emissions and locations of emission sources. Model output is compared with continuous observations, data collected from field campaigns, and previous modelling efforts. The WRF-SMOKE-CMAQ modelling framework is able to capture the changes in both the magnitude of the ozone concentrations and its spatial behaviour over the period of study. Many of the simulations show that the highest ozone concentrations occur outside the area sampled by the fixed monitoring network and within the LFV's numerous tributary valleys. Not all modelled episodes achieved the same agreement with observations and some of these discrepancies are likely related to shortcomings in the meteorological modelling. The model consistently overpredicts ozone at a number of stations within the City of Vancouver and underpredicts daytime NOx concentrations there. Both results are consistent with a deficiency in NOx emissions. The model shows a changing bias over time which also suggests uncertainties in the emission backcasting.

RWDI Air Inc. | Date: 2010-03-24

A wall assembly for mixing polluted air with less polluted air to provide moderately polluted air. The wall assembly includes means for dividing air from the roadway region into a lower part and an upper part, and means for permitting at least a portion of the upper part to flow substantially in one or more flow directions toward the leeward region. The wall assembly also includes means for directing the lower part substantially upwardly in a direction substantially transverse to the flow direction to intersect with the upper part and to mix the polluted air with said less polluted air, to provide the moderately polluted air proximal to the leeward area.

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