The Canadian FTIR Observing Network (CAFTON) is a network of Fourier transform infrared (FTIR) spectrometers deployed across Canada. CAFTON coordinates the measurements of these spectrometers and integrates the atmospheric data with two atmospheric models to characterize atmospheric composition, determine transport pathways, and identify pollutant sources across Canada. Another purpose of CAFTON is to provide training to a new generation of atmospheric scientists. Students and post-doctoral fellows are fully engaged in CAFTON, gaining expertise in both measurement and modelling techniques.
Infrared spectroscopy provides a powerful technique for detecting trace gases and has been used to measure atmospheric composition from the ground, balloons, and aircraft since the 1960s. FTIR spectrometers offer high spectral resolution, wide spectral coverage, and excellent throughput, which enables the measurement of many species simultaneously. The CAFTON FTIR spectrometers collect measurements of atmospheric composition that are used to help understand atmospheric change, specifically air quality and climate change.
Air quality is generally monitored by measurements of “criteria air contaminants” that are correlated with adverse health consequences. The chemical and dynamical relationships between these species and their precursors are complex and non-linear. Changes in anthropogenic emissions and climate will alter these relationships and the oxidizing capacity of the troposphere. While an urban location like Toronto is clearly subject to pollution events, the Arctic also experiences poor air quality due to transport from mid-latitudes and biomass burning events. CAFTON contributes to the measurement of pollutants such as O3 and its precursors, carbon monoxide (CO), ethane (C2H6), and acetylene (C2H2) as well as monitoring their sources and sinks.
Increases in the concentrations of the greenhouse gases CO2 and CH4 are well documented. From 2000 to 2006, the rate of increase of CH4 levelled off, but recent measurements suggest increases in 2007 and 2008 that might be due to a combination of enhanced high-latitude emissions and tropical emissions. Knowledge of the global distribution of the sources and sinks of these gases is critical to understanding the carbon cycle and assessing their feedbacks to warming. CAFTON instruments are important in increasing the global coverage of greenhouse gas measurements and investigating their sources, sinks, and transport.
CAFTON employs two atmospheric models to assess and interpret the FTIR measurements in terms of atmospheric processes from large scales down to local scales. The two models are the GEOS-Chem model and the STILT model. GEOS-Chem is a global chemical transport model driven by assimilated meteorological data from the NASA Goddard Earth Observing System (GEOS) and includes a complete description of tropospheric O3 -NOx-hydrocarbon chemistry. The Stochastic Time-Inverted Lagrangian Transport (STILT) model is a regional particle dispersion model that transports air parcels backwards in time, allowing the retrieval of the sensitivity of atmospheric tracer concentrations measured at receptor points with respect to upwind source regions. The models enable identification and quantification of the sources, sinks, and interactions between species, interpretation of the measurements in terms of transport processes, and an evaluation of emissions inventories. The daily, seasonal, and interannual variability of tropospheric concentrations, as well as any trends discernible over the longer time series, are also assessed.