Influence of Atmospheric Stability on PM2.5 Concentration in three Geographical Regions in the Northern Hemisphere

Aerosols are a component of air pollutants which leads to both health and atmospheric concerns. Thus, scientific findings would help minimizing the associated problems. We worked with PM2.5, which are particles less than 2.5 micrometers of diameter. We used a concept called Heat Deficit (HD) to represent the atmospheric stability. When a region has high HD, less heat exists so the atmosphere is more stable. As a result, air pollution concentration is high. When the HD is less, a lot of heat remains in the area, so air pollution is low due to atmospheric turbulence.

To represent the Northern Hemisphere, we selected three cities; Fairbanks in Alaska, Milan in Italy, and Beijing in China. Those corresponds to Western, Central and the Eastern parts of the Northern Hemisphere. All three cities are located in valleys, which usually experience more pollution compared to flat regions. We were concerned about winter season, so we considered five winters for each valley starting November 1^st of the previous year till the end of February of next year. We used University of Wyoming’s sounding data to calculate HD and did the analysis for each winter and all five winters combined. Both geographical and meteorological conditions vary among three cities, for an example Fairbanks is a small city with heavy snow fall while Beijing is a large city with almost no snowfall. Milan has characteristics lie between Fairbanks and Beijing.

Just by looking at the scatter plots or time series of daily average PM2.5 against daily average HD at 925 mb, it was not possible to clearly distinguish patterns between the cities. But the equation corresponds to linear fit provided valuable insights. Case with all winters combined was quite similar to each winter separately. When considering all five winters combined, the gradients were 2.9, 8.6, and 51 for Fairbanks, Milan, and Beijing. In other words, to recover one unit of HD, Milan emits 3 times more PM2.5 compared to Fairbanks, and Beijing emits ~18 times more. On the other hand, if the heat reaches the equilibrium condition, Milan has the highest PM2.5 level among three valleys followed by Beijing and Fairbanks.