Assessment of the spatial distribution of potential sources of atmospheric aerosol based on photometric measurements in the Middle Urals

Atmospheric aerosol is characterized by significant temporal and spatial variability and plays a key role in many atmospheric processes. The need for a detailed study of the spatial distribution of particles is due to the diversity of aerosol sources in the atmosphere, as well as the negative impact of some types of aerosols on human health. 

Our aim of this study is to identify the main geographic source regions of different types of aerosols based on spectral values of aerosol optical depth (AOD) collected in the Middle Urals as part of the global atmospheric aerosol monitoring program AERONET (https://aeronet.gsfc.nasa.gov/).

L. Ashbaugh method is employed to evaluate the source fields of atmospheric pollutants. This method is based on finding the Potential Source Contribution Function (PSCF). Function PSCF links measurement results with backward air mass trajectories, allowing for the identification of regions containing probable sources of atmospheric aerosols.

The geographic area was divided by a grid into cells with indices (i,j), where i and j number the geographic coordinates ̶ longitude and latitude of the center of the selected cell.

The function PSCF calculates the probability of a particular area contributing to the particular of aerosol type at an observation site. The PSCF for the ij-th cell is defined as the ratio of the number of trajectories passing through that cell and delivering a particular of aerosol type (m_ij) to the total number of trajectories passing through that cell (n_ij).

Classification of regional types of aerosol was performed by the spectral values of AOD by the method of k-means. The spectral values of extinction coefficients calculated with the use of MOPSMAP software from data of MUrA regional aerosol model and CALIPSO global model we defined as initial centers of clusters. As a result, five types of aerosols were identified: Dust, Clean Ccontinental, Polluted Continental/Smoke, Polluted Dust, and Elevated Smokes.

We analyzed on air mass transport to the point, located in the Middle Urals (at the AERONET site, Ekaterinburg, (57.038 N, 59.545 E), obtained with the Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT) since 2007 till 2020. Three-dimensional fields of meteorological parameters of the Northern Hemisphere obtained from the archive of the Global Data Assimilation System (GDAS1) database from the server hftp://arlftp.arlhq.noaa.gov/archives/gdas1/ were used to calculate the air trajectories.

The obtained results demonstrate a clear spatial differentiation of atmospheric aerosol sources for some different types. High PSCF values (more than 0.6) for elevated smoke are concentrated in the region of Western Siberia. This is due to the periodic intense forest fires that occur in this region. For dust aerosols the maximum PSCF values exceed 0.8 and are localized in the southern regions, including steppe areas of Kazakhstan. Here the main sources are natural processes - dust storms and soil erosion. For other types of aerosols PSCF values are lower than 0.5, which does not allow to interpret their sources as significant.

We are grateful to our colleagues M.V. Panchenko, S.M. Sakerin, S.Yu Gorda, S.A. Beresnev, Yu.I. Markelov, B.N. Holben, and A.V. Smirnov for assistance in photometric measurements at the AERONET aerosol monitoring station in the Middle Urals.

The study was supported by the Ministry of Science and Higher Education of the Russian Federation, project FUMN-2024-0004.