High-resolution quantification of atmospheric CO<sub>2</sub> mixing ratios in the Greater Toronto Area, Canada

Abstract

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...