P. A. Makar

Comparison of Canadian air quality forecast models with tropospheric ozone profile measurements above midlatitude North America during the IONS/ICARTT campaign: Evidence for stratospheric input

[1]xa0During July and August, 2004, balloon-borne ozonesondes were released daily at 12 sites in the eastern USA and Canada, producing the largest single set of free tropospheric ozone measurements ever compiled for this region. At the same time, a number of air quality forecast models were run daily as part of a larger field experiment. In this paper, we compare these ozonesonde profiles with predicted ozone profiles from several versions of two of these forecast models, the Environment Canada CHRONOS and AURAMS models. We find that the models show considerable skill at predicting ozone in the planetary boundary layer and immediately above. Individual station biases are variable, but often small. Standard deviations of observation-forecast differences are large, however. Ozone variability in the models is somewhat higher than observed. Most strikingly, none of the model versions is able to reproduce the typical tropospheric ozone profile of increasing mixing ratio with altitude. Results from a sensitivity test suggest that the form of the ozone lateral boundary condition used by all model versions contributes significantly to the large ozone underpredictions in the middle and upper troposphere. The discrepancy could be reduced further by adding a downward flux of ozone from the model lid and by accounting for in situ production of ozone from lightning-generated NOx.

Summertime formaldehyde at a high‐elevation site in Quebec

Measurements of formaldehyde were made during the summer of 1996 at a high-elevation site in Quebec as part of the North American Research Strategy on Tropospheric Ozone-Canada East (NARSTO-CE) measurement program. Gas phase mixing ratios were determined continuously by removing formaldehyde from the air in a glass coil scrubber, and producing a fluorescent dimer through the Hantzsch reaction. Average mixing ratios of formaldehyde were 1.3 and 0.8 ppbv for dry and wet periods, respectively. Highest values of HCHO were observed July 1-2 with a maximum mixing ratio of 4.6 ppbv. Fog water samples were also collected and analyzed for HCHO on five afternoon periods. Comparison of HCHO in the gas and aqueous phases shows reasonable agreement with Henrys law equilibrium. For dry periods July 1-12, relationships were examined between formaldehyde and other chemical species also measured at the site. Data were segregated based on the ratio of NO x to NO y and on the level of anthropogenic hydrocarbons present in the air mass. For the majority of the data, formaldehyde increased with both ozone and products of NO x oxidation (NO z ) and was inversely related to the NO x /NO y ratio. During the high HCHO episode July 1-2, HCHO was correlated with neither ozone nor NO 2 illustrating the different chemistry at the site on these days. A chemical box model was used to examine sources of HCHO July 1-4. The model suggests that biogenic hydrocarbons contribute on average 53% of the locally produced formaldehyde, the remainder resulting from the oxidation of methane (19%), anthropogenic VOCs (16%), acetaldehyde (7%), and organic peroxides (3%). The model cannot account for the July 1-2 formaldehyde mixing ratios from the chemistry measured at the site. This implies that an additional HCHO source not included in the model was responsible for the high levels on those days.

Measurement and modeling of particle nitrate formation

Nighttime measurements of particle number distribution and mass composition, and concentrations of NO2, O3, NH3, and HNO3, were made at night at a rural site in Ontario in August of 1992. A simple model of particle growth was constructed to simulate the observed rapid growth of aerosol mass in the 0.2 to 0.5 μm diameter range. Both measurements and model results indicate that the growth of accumulation mode aerosol mass was due to condensation of the nitrate radical, HNO3, and NH3 onto particles, with the formation of particle ammonium nitrate. The results show that the reaction of O3 with NO2 in the isolated nocturnal boundary layer can lead to the production of gas-phase nitric acid. When this occurs in the presence of local ammonia emissions and preexisting particles, rapid growth of particle ammonium nitrate takes place. The model results show that most of the observed variations can be accounted for by a coupled system of equations including dynamical and thermodynamic effects. The dynamical approach to equilibrium is sufficiently fast that the gas-phase nitric acid concentrations are more sensitive to the magnitude of the thermodynamic equilibrium concentration than the dynamical time constant. A simple parameterization for the effects of sulphate on particle nitrate formation was developed and shown to provide a good estimate of the equilibrium concentration of gas-phase nitric acid.

Effects of black carbon aging on air quality predictions and direct radiative forcing estimation

An aging scheme for black carbon (BC) aerosol was implemented into a regional air-quality forecast model to study the impact of BC aging on air quality predictions. Three different assumptions for the mixing state of BC—external mixture, internal mixture and gradual aging—were used to simulate the distribution of BC particles over North America in April 2002. Cloud –condensation nuclei number and BC wet deposition rate increased significantly and BC mass column loading decreased as a result of BC aging. With the gradual aging process incorporated into the model, the comparison of ground level BC concentration predictions with surface observations was slightly improved. Estimation of the average direct radiative forcing of BC over the spatial domain of this study showed that the factor of direct forcing enhancement by BC aging was much smaller than the mixing state effect factor. The effect of increased wet deposition due to aging compensated partially for the effect of increased absorbance suggesting that the change in the hygroscopic properties of BC due to aging must be taken into account to quantify accurately the effect of BC aging on climate.

Relative impact of windblown dust versus anthropogenic fugitive dust in PM2.5 on air quality in North America

[1]xa0A new windblown dust emissions module was recently implemented into A Unified Regional Air Quality Modeling System (AURAMS), a Canadian regional air quality model, to investigate the relative impact of windblown dust versus anthropogenic fugitive dust on air quality in North America. In order to apply the windblown dust emissions module to the entire North American continent, a soil grain size distribution map was developed using the outputs of 4 monthly runs of AURAMS for 2002 and available PM2.5 dust content observations. The simulation results using the new soil grain size distribution map showed that inclusion of windblown dust emissions is essential to predict the impact of dust aerosols on air quality in North America, especially in the western United States. The windblown dust emissions varied widely by season, whereas the anthropogenic fugitive dust emissions did not change significantly. In the spring (April), the continental monthly average emissions rate of windblown dust (4.1 × 107 kg/d) was much higher than that of anthropogenic fugitive dust (1.5 × 107 kg/d). The total amount of windblown dust emissions in North America predicted by the model for 2002 was comparable to that of anthropogenic fugitive dust emissions. Even with the inclusion of windblown dust emissions, however, the model still had difficulty simulating dust concentrations. Further improvements are needed, in terms of both limitations of the windblown dust emission module and uncertainties in the anthropogenic fugitive dust emissions inventories, for improved dust modeling.

Contributions of natural and anthropogenic sources to ambient ammonia in the Athabasca Oil Sands and north-western Canada

Atmospheric ammonia (NH3) is a short-lived pollutant that plays an important role in aerosol chemistry and nitrogen deposition. Dominant NH3 emissions are from agriculture and forest fires, both of which are increasing globally. Even remote regions with relatively low ambient NH3 concentrations, such as northern Alberta and Saskatchewan in northern Canada, may be of interest because of industrial oil sands emissions and a sensitive ecological system. A previous attempt to model NH3 in the region showed a substantial negative bias compared to satellite and aircraft observations. Known missing sources of NH3 in the model were re-emission of NH3 from plants and soils (bidirectional flux) and forest fire emissions, but the relative impact of these sources on NH3 concentrations was unknown. Here we have used a research version of the high-resolution air quality forecasting model, GEM-MACH, to quantify the relative impacts of semi-natural (bidirectional flux of NH3 and forest fire emissions) and direct anthropogenic (oil sand operations, combustion of fossil fuels, and agriculture) sources on ammonia volume mixing ratios, both at the surface and aloft, with a focus on the Athabasca Oil Sands region during a measurement-intensive campaign in the summer of 2013. The addition of fires and bidirectional flux to GEM-MACH has improved the model bias, slope, and correlation coefficients relative to ground, aircraft, and satellite NH3 measurements significantly. By running the GEM-MACH-Bidi model in three configurations and calculating their differences, we find that averaged over Alberta and Saskatchewan during this time period an average of 23.1 % of surface NH3 came from direct anthropogenic sources, 56.6 % (or 1.24 ppbv) from bidirectional flux (re-emission from plants and soils), and 20.3 % (or 0.42 ppbv) from forest fires. In the NH3 total column, an average of 19.5 % came from direct anthropogenic sources, 50.0 % from bidirectional flux, and 30.5 % from forest fires. The addition of bidirectional flux and fire emissions caused the overall average net deposition of NHx across the domain to be increased by 24.5 %. Note that forest fires are very episodic and their contributions will vary significantly for different time periods and regions. This study is the first use of the bidirectional flux scheme in GEM-MACH, which could be generalized for other volatile or semi-volatile species. It is also the first time CrIS (Cross-track Infrared Sounder) satellite observations of NH3 have been used for model evaluation, and the first use of fire emissions in GEM-MACH at 2.5 km resolution. Published by Copernicus Publications on behalf of the European Geosciences Union. 2012 C. H. Whaley et al.: Sources of atmospheric NH3 in Alberta and Saskatchewan

Recent Advances in Canada’s National Operational AQ Forecasting System

Environment Canada routinely issues twice-daily, 48-h public forecasts of (a) gridded surface and near-surface O3, PM2.5, and NO2 concentration fields made by the GEM-MACH15 on-line chemical weather forecast model on a 15-km North American grid plus (b) point-specific forecasts for Canadian cities of the national Air Quality Health Index (AQHI) prepared by a statistical post-processing package called UMOS-AQ. The AQHI is a health-based, additive, no-threshold, hourly AQ index that ranges from 0 to 10+ and is based on a weighted sum of local O3, PM2.5, and NO2 concentrations. An objective analysis scheme for surface O3, PM2.5, and NO2, which will provide model-measurement data fusion and model error diagnostics, is now being tested. These recent advances as well as plans for further improvements to the AQ forecasting system are described.

Comprehensive Surface-Based Performance Evaluation of a Size- and Composition-Resolved Regional Particulate-Matter Model for a One-Year Simulation

A comprehensive performance evaluation has been carried out for the first annual simulation made with AURAMS, a size- and composition-resolved, off-line, regional particulate-matter (PM) modelling system. The year simulated was 2002, the modelling domain covered most of North America, and the horizontal grid size was 42 km. The large evaluation data set consisted of filter-based and con- tinuous surface air-chemistry measurements made by five Canadian and U.S. net- works and precipitation-chemistry measurements made by seven Canadian and U.S. networks. Completeness criteria were used to exclude stations with incomplete records, and units conversions were performed to maximize uniformity and com- parability. Quantities used in the performance evaluation included annual air con- centrations of SO2, NO2, O3, HNO3, PM2.5, PM10, PM2.5-SO4, PM2.5-NO3, PM2.5-NH4, PM2.5-CM, PM2.5-EC, and PM2.5-TOM, and annual concentrations in precipitation of SO4 = , NO3 - , and NH4 + . The extensive evaluation has allowed inferences about factors contributing to some model weaknesses.

Current and Future Developments in Numerical Air Quality Forecasting in Canada

Environment Canada produces twice-daily, 48-h operational air quality (AQ) forecasts for a domain covering North America. At the core of the forecast system is the GEM-MACH model, an on-line coupled meteorology and chemistry model that includes a representation of gas-phase, aqueous-phase, and heterogeneous chemistry and a number of particulate matter (PM) processes. In this paper, a brief description of the recent changes to the Canadian National AQ Forecasting System is given, followed by a discussion of future development plans. The objective for the next version of the system is to deliver improved AQ forecasts by improving initial and boundary conditions and representations of emissions and processes.

Satellite-derived emissions of carbon monoxide, ammonia, and nitrogen dioxide from the 2016 Horse River wildfire in the Fort McMurray area

In May 2016, the Horse River wildfire led to the evacuation of ∼ 88 000 people from Fort McMurray and surrounding areas and consumed∼ 590 000 ha of land in Northern Alberta and Saskatchewan. Within the plume, satellite instruments measured elevated values of CO, NH3, and NO2. CO was measured by two Infrared Atmospheric Sounding Interferometers (IASI-A and IASI-B), NH3 by IASI-A, IASIB, and the Cross-track Infrared Sounder (CrIS), and NO2 by the Ozone Monitoring Instrument (OMI). Daily emission rates were calculated from the satellite measurements using fire hotspot information from the Moderate Resolution Imaging Spectroradiometer (MODIS) and wind information from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis, combined with assumptions on lifetimes and the altitude range of the plume. Sensitivity tests were performed and it was found that uncertainties of emission estimates are more sensitive to the plume shape for CO and to the lifetime for NH3 and NOx . The satellite-derived emission rates were ∼ 50–300 kt d−1 for CO, ∼ 1–7 kt d−1 for NH3, and∼ 0.5–2 kt d−1 for NOx (expressed as NO) during the most active fire periods. The daily satellite-derived emission estimates were found to correlate fairly well (R ∼ 0.4–0.7) with daily output from the ECMWF Global Fire Assimilation System (GFAS) and the Environment and Climate Change Canada (ECCC) FireWork models, with agreement within a factor of 2 for most comparisons. Emission ratios of NH3/CO, NOx/CO, and NOx/NH3 were calculated and compared against enhancement ratios of surface concentrations measured at permanent surface air monitoring stations and by the Alberta Environment and Parks Mobile Air Monitoring Laboratory (MAML). For NH3/CO, the satellite emission ratios of ∼ 0.02 are within a factor of 2 of the model emission ratios and surface enhancement ratios. For NOx/CO satellite-measured emission ratios of ∼ 0.01 are lower than the modelled emission ratios of 0.033 for GFAS and 0.014 for FireWork, but are larger than the surface enhancement ratios of ∼ 0.003, which may have been affected by the short lifetime of NOx . Total emissions from the Horse River fire for May 2016 were calculated and compared against total annual anthropogenic emissions for the province of Alberta in 2016 from the ECCC Air Pollutant Emissions Inventory (APEI). Satellite-measured emissions of CO are ∼ 1500 kt for the Horse River fire and exceed the total annual Alberta anthropogenic CO emissions of 992.6 kt for 2016. The satellite-measured emissions during the Horse River fire of ∼ 30 kt of NH3 and ∼ 7 kt of NOx (expressed as NO) are approximately 20 % and 1 % of the magnitude of total annual Alberta anthropogenic emissions, respectively. Published by Copernicus Publications on behalf of the European Geosciences Union. 2578 C. Adams et al.: Satellite-derived emissions of CO, NH3, and NO2 from the 2016 Horse River wildfire