Opportunities, Constraints, and Progress of a Mid-Cost Sensor Network for In Situ Greenhouse Gas and Air Quality Monitoring in the Greater Toronto Area

In 2021, the city of Toronto adopted a plan to reach net-zero emissions by 2040 that includes ambitious strategies to be implemented over the coming years. The purpose of the Toronto Atmospheric Monitoring of Emissions (TAME) project is to produce measurements of greenhouse gases and air pollutants in the urban area in order to quantify emissions during this period and study air quality co-benefits of emissions reduction strategies. Instrumentation operated as part of TAME includes ground-based column measurements and in situ measurements. Many of the in situ measurements are made with mid-cost sensor packages. One is the QuantAQ Modulair, which measures CO, NO_X, O₃, and particulate matter, and the other is a CO₂ sensor built by Environment and Climate Change Canada. Since August 2024, these sensors have been evaluated against reference instrumentation and deployed at eight sites around the Greater Toronto Area. The pollutant concentrations are calculated using regression models based on colocation with reference instrumentation; we also employ one pair of sensors as a travel standard to assess changes in the sensors’ performance while they are deployed at their respective sites and revise the regression models as needed. We also maintain a set of QuantAQ sensors permanently colocated with our reference instruments throughout the deployment period. The advantages and disadvantages of these calibration approaches will be discussed and compared to other methodologies. A summary of pollutant trends among the sites will be presented with emphasis on what can be confidently quantified given both the spatial gradients and the performance limitations of these sensors.