Praxis/Urban unit installed at Fairbanks, Alaska.
During the cold Arctic winter, local emissions (e.g. from traffic, home-heating) can become trapped near the surface in remote Arctic cities such as Fairbanks, Alaska. These conditions cause very high levels of air pollution that exceed air quality standards. To better quantify these air pollution episodes, Praxis/Urban instruments were deployed in Fairbanks to measure gases (CO, NO, NO2, O3) and fine particulate matter (PM2.5) during the Arctic winter of 2019.
Praxis data was cross-compared to reference Air Quality Monitors over a 2 week period, showing good agreement.
The Praxis units then ran autonomously under the cold Arctic conditions with ambient temperatures as low as -30 ˚C. Praxis instruments have since been deployed over two Arctic winter seasons at locations across Fairbanks, operating continuously down to -40 ˚C, and generating a vast and highly valuable dataset on Arctic air pollution, the analysis of which is the focus of ongoing scientific research.
The figure illustrates how winter pollution levels were elevated in Fairbanks during early December when ambient temperatures descended to nearly -30 ˚C as surface air pressure increased. Concentrations of particulate matter (PM2.5) and gases (CO, NO, NO2) increased and ozone (O3) was completely destroyed (titrated) by reaction with NO.
During mid-December the ambient temperatures were higher. Surprisingly, high levels of air pollution were again encountered, with particularly high gas concentrations. Further analysis of the data is now being undertaken to better characterise these pollution episodes and understand their underlying causes in terms of the local emissions and changing atmospheric conditions.
1/ A very close agreement is demonstrated between the Praxis/Urban PM2.5 data (purple line) and reference Air Quality Monitors (black line).
2/ Measurement of PM2.5 by the Praxis/Urban (~2 min averages) show good agreement to BAM AQ Monitor (hourly), and identify rapid temporal variability in PM2.5 that cannot be seen by the hourly BAM AQ Monitor.
3/ The Praxis PM2.5 particulate sensor was found to operate successfully at low temperatures without requiring temperature corrections, unlike other instruments tested. The presented data on PM2.5 include an estimate for the mass of particles with diameter less than the 0.35 µm detection threshold of optical particle counters.
4/ Measurements of four gases (CO, NO, NO2, O3) by the Praxis/Urban (coloured lines) also show very good agreement to the Air Quality Monitors (black lines) with data presented as 5 minute averages.
5/ Dependencies of the small gas sensors on temperature (and humidity) were characterised by comparison to the Air Quality monitors and corrected using analysis algorithms. The results yield strong agreement with R2 > 0.9 during the campaign.
The Praxis instruments have since been deployed at several locations across Fairbanks during the Arctic winter in order to better characterise emissions and pollution exposure in the different regions.
To find out more about how Praxis/Urban (and other products) can be used to provide accurate air quality monitoring data in the field, please view products and data sheets or contact David Johnson.
Roberts et al. “In-situ characterization of layered pollution in the wintertime Arctic atmosphere by small sensors” Presentation EGU21-15351 at the European General Assembly, April 2021. Acknowledgements to ADEC and ALPACA/CASPA consortium and IPEV/LEFE for funding.
