New insights into submicron particles impact on visibility

The aim of the study was to analyze the impact of very fine atmospheric particles (submicron particulate matter; PM₁) on visibility deterioration. Taking into consideration not only their entirely different physio-chemical properties in comparison to a well-recognized PM₁₀ but also the origin and a growing environmental awareness of PM₁, the main research problem has been solved in few steps. At first, the chemical composition of PM₁ was determined in two selected urban areas in Poland. Measurements of meteorological parameters, i.e., air temperature and humidity, precipitation, atmospheric pressure, wind speed, and visibility, were also conducted. The next step of the work was the analysis of (1) seasonal changes of the concentration of PM₁ and its main components, (2) the influence of chemical components of PM₁ on light extinction, and (3) the influence of PM₁ and humidity on visibility. Hierarchical cluster analysis, correlation matrixes and a heat map, and classification and regression tree analysis were used. The light extinction coefficient is influenced mainly by coarse mass of PM, and PM₁-bound ammonium nitrate, organic matter, and by Rayleigh scattering. The less important in the light extinction coefficient shaping has PM₁-bound ammonium sulfate, elemental carbon, and soil. In this way, the secondary origin PM₁ components were proved to most significantly influence the visibility. The obtained results confirmed the possibility of the use of statistical agglomeration techniques to identify ranges of variation of visibility, including independent variables adopted to analyses (meteorological conditions, chemical composition of PM₁, etc.).