Investigating Transported and Local Carbon Monoxide in the Southern Hemisphere with Satellite and Ground-based Remote Sensing

Distinguishing the relative contribution of transported and local sources of atmospheric pollution is fundamental to developing realistic air quality policies and providing accurate air quality forecasts. We use the different sensitivities of satellite and ground based remote sensing instruments to provide complementary information about sources of carbon monoxide (CO). Total column amounts of CO are compared between the satellite-borne Measurements of Pollution in the Troposphere (MOPITT) and ground-based solar FTIR instruments in the TCCON and NDACC measurement networks. Observations are compared at three Southern Hemisphere stations: Darwin and Wollongong in Australia and Lauder in New Zealand. MOPITT has maximum sensitivity in the free troposphere and measurements are used to interpret long-range transport from continental sources. However, satellite measurements provide limited fine-scale information due to sparse measurement timing and spatial averaging, often missing local pollution events. In contrast, ground-based solar-tracking FTIR instruments have enhanced sensitivity closer to the surface, and can help interpret fine-scale chemistry and dynamic influence. However, FTIR measurements are limited to one location and have trouble interpreting transported signals.

Anomalies in the CO timeseries from each instrument are discussed in relation to pollution delivery pathways of local, regional and long-distance origin. While large-scale pollution events are captured by both instruments, only the satellite instrument can provide regional and global context. For example, the wider geographical impact of Australian fires, such as the severe bushfires around Canberra in 2003, can be traced in the satellite observations and resulting CO plumes tracked out across the Pacific Ocean. MOPITT can also be used to track long-range transport of pollution from biomass burning in South America and southern Africa, reflecting the hemispheric impact of these sources. In comparison, the FTIR can additionally capture local urban and biomass burning influences. Seasonal and interannual variability of CO is significantly different at each site. The roles of emissions and meteorology in CO variability is investigated using global atmospheric modeling with CAM-chem. These modeling studies help quantify the relative impact of local and remote pollution sources to total column CO at the three stations.