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

Abstract

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.

Observing local CO<sub>2</sub> sources using low-cost, near-surface urban monitors

“…Data availability. All BEACO 2 N CO 2 observations used in this analysis can be downloaded at https://doi.org/10.5281/zenodo.1206983 (Shusterman and Cohen, 2018). Traffic counts are available on the California Department of Transportation website (http://pems.dot.ca.gov/, last access: 23 September 2018); wind, temperature, and humidity observations are available on the NOAA Integrated Surface Database website (http://www.ncdc.noaa.gov/isd/, last access: 23 September 2018); and boundary layer heights are available on the ECMWF website (http://apps.ecmwf.int/datasets/, last access: 23 September 2018).…”

Integrated urban services: Experience from four cities on different continents

“…the mean daily cycle for winter 2016. Pugliese et al (2018) showed that the novel SOCE inventory displays the best performance with only minor deviations from observed atmospheric CO 2 at the Downsview measurement site as seen in Fig. 7.…”

“…Currently, four atmospheric measurement sites are operated in the GTHA area all of which include CO 2 and CH 4 as well as additional proxies like CO, N 2 O, δ 13 CO 2 , Δ 14 CO 2 , and 222 Radon at some sites. ECCC and the University of Toronto have successfully built a high-resolution (2.5 × 2.5 km 2 ) emission inventory 'SOCE' (Southern Ontario Carbon Emission) for CO 2 based on air quality emission maps for the TO15 domain (Pugliese et al, 2018). Significant differences of up to 40% for total annual emissions were found in the urban domain when compared to existing inventories.…”

“…Mean daily cycle of CO 2 at the Downsview station: measured (blue), simulated using the SOCE inventory (red) and simulated using the Fossil Fuel Data Assimilation System FFDAS V2 inventory (green), adapted fromPugliese et al, 2018. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article. )…”

Statistical characterization of urban CO2 emission signals observed by commercial airliner measurements

“…For effective mitigation actions against climate change, various independent approaches must be used to reduce the uncertainties associated with citywide greenhouse gas emissions estimates, and one of those approaches can be provided by atmospheric CO 2 observations 12 . For this purpose, atmospheric CO 2 measurements focusing on urban areas have been examined in recent years by means of citywide in-situ ground measurement networks [13][14][15][16] or satellite measurements 17,18 . The former methodology provides dense and accurate data and the latter broad spatial coverage, whilst both also have limitations.…”