A new approach of the normalization relationship between PM2.5 and visibility and the theoretical threshold, a case in north China.

Both PM 2.5 and visibility are important physical parameters to measure the air pollution condition. This paper first provided a new normalization approach for the relationship between PM 2.5 and visibility in heavy pollutant region, which realized a mathematical calculation for two different physical parameters based on non-dimensional data process (also called Min-Max normalization). The normalization relationship showed a power function (y = axb) with high correlation coefficients. The inflection points of the maximum power function curvature composed the theoretical threshold range of PM 2.5 for improving or deteriorating the visibility. In the case city of north China, the threshold range of PM 2.5 was 112–121 μg·m−3 corresponding to the visibility range 4.5–5.9 km. Within the threshold range, the mean concentration of main pollutant components was 106 μg·m−3. The mean extinction coefficient, b ext of 743.5 Mm−1, was mainly contributed by organic matter (34%), ammonium nitrate (19%), ammonium sulfate (18%) and elemental carbon (13%). When PM 2.5 was below the range, the visibility increased significantly with the slow decrease of PM 2.5. When PM 2.5 exceeded the range, the visibility reduced seriously due to the saturated extinction contribution of the main pollutants. The new normalization approach theoretically revealed the significance of threshold and how to improve visibility by controlling PM 2.5 at different pollution stages. Unlabelled Image • A new normalization approach was first applied to establish the mathematical relationship of PM 2.5 and visibility. • The normalization mathematical relationship was a power function with high correlation coefficients. • The maximum curvature of the function composed the theoretical threshold of PM 2.5 to improve or deteriorate visibility. • The extinction coefficients of aerosol components were quite different at different pollution stages. • The threshold range has guiding significance how to control PM 2.5 for the blue sky in heavy polluted cities. [ABSTRACT FROM AUTHOR]