MardiSciences:

The Arctic atmosphere is impacted by significant particulate pollution known as “Arctic Haze.” Numerous studies have attributed this haze to the transport of pollutants from mid-latitude regions of Asia and Europe. However, for several decades, the Arctic region has experienced increased human activity, partly due to mining and oil extraction operations. Climate change, which is occurring four times faster in the Arctic than the global average, is partly responsible for this development. Many studies have shown that local sources of pollution significantly affect air quality in high-latitude cities. For instance, Fairbanks, located in central Alaska, is among the most polluted cities in the U.S. during winter. Fairbanks is affected by emissions from fuel- and coal-powered power plants, road transport, and individual heating using wood, coal, or diesel. Moreover, emissions are even higher when temperatures drop (reaching as low as -40°C). But it is Fairbanks’ topography, situated in a valley, and the frequent temperature inversions in the boundary layer that lead to particularly stable weather conditions, trapping pollution near the surface and deteriorating air quality. However, there are still many uncertainties regarding pollution sources and the processes of secondary aerosol formation in cold, dark winter conditions.

The ALPACA (Alaskan Layered Pollution and Chemical Analysis) campaign took place in January-February 2022 to collect data on atmospheric composition and meteorology and to address these questions. The MICROMEGAS instruments, developed at LAERO using low-cost miniature electrochemical sensors, were deployed on this occasion to document the spatio-temporal variability of gaseous pollutants (CO/NO/NO₂ and O₃). The instruments were mounted on vehicles to map pollution in the city and the surrounding hills, while flights on the tethered balloon or Helikite from EPFL enabled profiling of pollution in the boundary layer. These instruments also spent several days at the ALPACA monitoring site in the city center, equipped with reference analyzers for calibration and validation. When weather conditions were favorable, balloon flights sampled pollution plumes from power plant chimneys trapped in altitude inversion layers. Thanks to the increased precision of calibrated MICROMEGAS data, the analysis of relationships between various pollutants within the plumes made it possible to identify their origin and assess simulations from a Lagrangian numerical model used to quantify the power plants’ impact on surface air quality.