Analysis and estimation of gaseous air pollutant emissions emitted into the atmosphere during Manavgat and Milas wildfire episodes using remote sensing data and ground measurements

What is it about?

In this study, the concentration levels of CO, NO2, CH2O, SO2, and O3 gases emitted during the two biggest wildfire episodes observed in Manavgat and Milas, Türkiye in 2021 were analyzed and spatio-temporal gas concentrations were estimated. Using the remote sensing imagery from Sentinel-5P satellite, a daily based time-series data analysis was performed over the Google Earth Engine platform (GEEp) and the gas emission levels (mol/m2) during the wildfires were obtained. The processed time-series data has been associated with the measurements from ground-stations of Türkiye National Air Quality Monitoring Network, allowing unit conversion to gas concentration unit in μg/m3. Based on predicted gas concentrations, statistical performance measurements were calculated with actual ground-station measurements. According to the spatio-temporal gas concentrations, the highest levels of CO gas emissions were detected on July 29th in Manavgat 5492.63 ± 325.12 μg/m3 and on August 5th in Milas 1071.14 ± 230.41 μg/m3. During the wildfire episodes NO2 concentration has reached to 383.52 ± 19.31 μg/m3 in Manavgat and 34.76 ± 8.20 μg/m3 in Milas. The O3 levels during the wildfires were estimated as 5.54 ± 16.09 μg/m3 in Manavgat and 41.22 ± 2.07 μg/m3 in Milas. The average SO2 concentration was 71.49 ± 4.2 μg/m3 in Manavgat and 165.35 ± 6.51 μg/m3 in Milas. Also, the average CH2O concentration was estimated as 12.83 ± 5.07 μg/m3 in Manavgat and 17.91 ± 4.41 μg/m3 in Milas. R2 values were between 0.67 and 0.84. Generally, IA values were higher than 0.70. The statistical results showed that our approach was reasonably successful in the prediction of the spatio-temporal wildfire gas emissions and can be applied to such scenarios.

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Photo by Marcus Kauffman on Unsplash

Photo by Marcus Kauffman on Unsplash

Why is it important?

The study conducted an assessment of wildfire gas concentration levels using ground-station measurements and Sentinel-5P satellite imagery data. Wildfires have significant adverse effects on human health and the nature and can be evaluated using satellite imagery together with ground-station measurements. Here, the concentration levels of CO, NO2, CH2O, SO2 and O3 gases emitted during the two biggest wildfire episodes observed in cities of Manavgat and Milas in Türkiye in 2021 were evaluated and spatio-temporal gas concentrations were estimated. In order to accomplish an acceptable correlation between satellite data and ground-level measurements, firstly, we captured Sentinel-5P satellite imagery data from GEEp and the ground-station measurements data published by The Ministry of Environment, Urbanization and Climate Change of Türkiye for the study period. We also used GEEp in daily time-series analysis by hand-coding for the period of the wildfires. Then, by interpolating actual data with the satellite data for all over the map we calculated individual unit conversion factors for each of the studied air pollutant gases that converts actual satellite imagery data in mol/m2 to environmentally interpretable unit μg/m3. Hence, we could produce spatio-temporal distribution maps and finally, made environmental assessments over the obtained interpretable air pollution data. However, in the absence of ground-station measurements, Sentinel-5P satellite imagery data cannot provide enough and interpretable pollution data limiting the users. Based on the correlation study between the unit converted satellite data in μg/m3 and actual ground-station data μg/m3, we obtained reasonably successful model accuracy and model agreement scores for the studied air pollutants. Generally, the air pollutant gas emission levels were much higher than the given threshold values. It was seen that the wildfire gas emission levels were clearly affected by meteorological conditions such as prevailing wind direction and wind speed, vegetation, dominant tree species, burned materials such as greenhouses, plastics and house materials at the fire-zone during the two wildfires. The air pollutant emission levels (μg/m3) in Manavgat wildfire were clearly higher than the levels observed in Milas wildfire, because the area burned in Manavgat wildfire were about three times higher than that of Milas wildfire, releasing much more gaseous emissions into the atmosphere. Spatio-temporal gas emission distribution gradients and time-series plots showed well-correlated data points for CH2O and CO gases considering the chemical formation kinetics of CH2O in the presence of CO with high temperatures at the both of the wildfires. This study concludes that the use of Sentinel-5P satellite imagery data together with the ground-level data is a suitable way for detecting and evaluating the emission of harmful gases over wildfire areas when conducting environmental assessment studies, showing its importance in protecting public health. According to the results from ground-level air pollutant emission estimations and statistical scores, our approach in processing of satellite imagery for the environmental assessment may provide a useful and practical way to understand and estimate spatio-temporal wildfire gas emissions levels considering meteorological conditions and local environment, and can be applied to similar scenarios when ground- level measurement data are available for the gas concentrations studied.