Abstract. Tropospheric ozone (O 3 ) 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 (NO x ) 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 Greater Toronto Area (GTA), we present an analysis of NO 2 , VOC and O 3 data from federal and provincial governmental monitoring sites in the GTA from 2000 to 2012. We show that, over the study period, summertime 24 h VOC reactivity and NO 2 midday (11:00-15:00) concentrations at all sites decreased significantly; since 2000, all sites experienced a decrease in NO 2 of 28-62 % and in measured VOC reactivity of at least 53-71 %. Comparing 2002Comparing -2003Comparing to 2011Comparing -2012, the summed reactivity of OH towards NO 2 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.

Pugliese, S., Jones, T., Preston, M. D., Hazlett, P., Tran, H. and Basiliko, N. 2014. Wood ash as a forest soil amendment: The role of boiler and soil type on soil property response. Can. J. Soil Sci. 94: 621–634. Wood ash is produced in large quantities in Canada as a by-product of the pulp and paper, sawmill, and bioenergy industries and it is anticipated that its disposal in landfills will not be a viable option. An alternative option may be to use it to amend forest soils. Wood ash is a complex mixture and its composition depends on several variables, including the combustion parameters of the boiler in which it is generated. We present an analysis of the amendment of two Canadian forest soils (a Brunisol from the Great Lakes–St. Lawrence and a Luvisol from the Carolinian forest regions of Ontario) with six different wood ashes collected from different biomass boilers through short-term controlled incubations. We show that following an 8-wk incubation period, amendment of the soils with wood ash led to small to moderate increases in soil pH, but had little effect on soil microbial activity and biomass. The concentration of important base cations such as calcium, magnesium and potassium as well as phosphorus generally increased in both soil types following amendment with different ash. This practice can return nutrients lost from forest ecosystems during harvesting; however, effects were found to be boiler-specific. Lastly, we show that four ash types led to small increases in cadmium in either soil; the concentration of all other measured heavy metals was not significantly increased following amendment, and in certain cases decreased, particularly with lead. The only potentially negative aspect encountered was elevated sodium, particularly with ash from one boiler, but unacceptable Na-absorptivity ratios were not exceeded. These results demonstrate that with proper characterization and selection of wood ash type and application rates, amendment of Canadian forest soils with wood ash may benefit forest ecosystems and is unlikely to disrupt the chemical and biological processes in soil environments.

Abstract. Many stakeholders are seeking methods to reduce carbon dioxide (CO2) emissions in urban areas, but reliable, high-resolution inventories are required to guide these efforts. We present the development of a high-resolution CO2 inventory available for the Greater Toronto Area and surrounding region in Southern Ontario, Canada (area of  ∼ 2.8 × 105 km2, 26 % of the province of Ontario). The new SOCE (Southern Ontario CO2 Emissions) inventory is available at the 2.5 × 2.5 km spatial and hourly temporal resolution and characterizes emissions from seven sectors: area, residential natural-gas combustion, commercial natural-gas combustion, point, marine, on-road, and off-road. To assess the accuracy of the SOCE inventory, we developed an observation–model framework using the GEM-MACH chemistry–transport model run on a high-resolution grid with 2.5 km grid spacing coupled to the Fossil Fuel Data Assimilation System (FFDAS) v2 inventories for anthropogenic CO2 emissions and the European Centre for Medium-Range Weather Forecasts (ECMWF) land carbon model C-TESSEL for biogenic fluxes. A run using FFDAS for the Southern Ontario region was compared to a run in which its emissions were replaced by the SOCE inventory. Simulated CO2 mixing ratios were compared against in situ measurements made at four sites in Southern Ontario – Downsview, Hanlan's Point, Egbert and Turkey Point – in 3 winter months, January–March 2016. Model simulations had better agreement with measurements when using the SOCE inventory emissions versus other inventories, quantified using a variety of statistics such as correlation coefficient, root-mean-square error, and mean bias. Furthermore, when run with the SOCE inventory, the model had improved ability to capture the typical diurnal pattern of CO2 mixing ratios, particularly at the Downsview, Hanlan's Point, and Egbert sites. In addition to improved model–measurement agreement, the SOCE inventory offers a sectoral breakdown of emissions, allowing estimation of average time-of-day and day-of-week contributions of different sectors. Our results show that at night, emissions from residential and commercial natural-gas combustion and other area sources can contribute > 80 % of the CO2 enhancement, while during the day emissions from the on-road sector dominate, accounting for > 70 % of the enhancement.

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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.

14Many stakeholders are seeking methods to reduce carbon dioxide (CO2) emissions in urban areas, 15 however reliable, high-resolution inventories are required to guide these efforts. We present the 16 development of a high-resolution CO2 inventory available for the Greater Toronto Area and 17 surrounding region in southern Ontario, Canada (area of ~2.8 x 10 5 km 2 , 26 % of the province of 18 Ontario). The new SOCE (Southern Ontario CO2 Emissions) inventory is available at the 2.5 x 2.5 km 19 spatial and hourly temporal resolution and characterizes emissions from seven sectors: Area, 20Residential natural gas combustion, Commercial natural gas combustion, Point, Marine, On-road and 21Off-road. To assess the accuracy of the SOCE inventory, we developed an observation-model 22 framework using the GEM-MACH chemistry-transport model run on a high-resolution grid with 2.5 23 km grid spacing coupled to the Fossil Fuel Data Assimilation System (FFDAS) v2 inventories for 24 anthropogenic CO2 emissions and the European Center for Medium-Range Weather Forecasts 25 (ECMWF) land carbon model C-TESSEL for biogenic fluxes. A run using FFDAS v2 for the southern 26Ontario region was compared to a run in which its emissions were replaced by the SOCE inventory. 27 Simulated CO2 mixing ratios were compared against in situ measurements made at four sites in 28 southern Ontario, Downsview, Hanlan's Point, Egbert and Turkey Point, in three winter months, 29 January-March, 2016. Model simulations had better agreement with measurements when using the 30 SOCE inventory emissions versus other inventories, quantified using a variety of statistics such as 31 correlation coefficient, root mean square error and mean bias. Furthermore, when run with the SOCE 32 inventory, the model had improved ability to capture the typical diurnal pattern of CO2 mixing ratios, 33 particularly at the Downsview, Hanlan's Point and Egbert sites. In addition to improved model-34 measurement agreement, the SOCE inventory offers a sectoral breakdown of emissions, allowing 35 estimation of average time-of-day and day-of-week contributions of different sectors. Our results 36show that at night, emissions from Residential and Commercial natural gas combustion and other 37 Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-678 Manuscript under review for journal Atmos. Chem. Phys. Discussion started: 26 July 2017 c Author(s) 2017. CC BY 4.0 License. 3Area sources can contribute > 80 % of the CO2 enhancement while during the day emissions from the 38On-road sector dominate, accounting for >70 % of the enhancement. 39 Introduction 40Urban areas are sites of dense population and the intensity of human activities (such as 41 transportation, industry and residential and commercial development) makes them hot-spots for 42 anthropogenic carbon dioxide (CO2) emissions. While occupying only 3 % of the total land area, urban 43 areas are locations of residence for 54 % of the global population and are the source of 53 -87 % of 44 anthropogenic CO2 emissions...

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