Measurements and Approximations for Submicron-Aerosol Size Distribution Functions

Results of field measurements taken in the near-Caspian (2002, 2003, 2007, 2009, 2010, 2011, 2013, 2014, 2016 years) and near-Aral sea (1998) deserts under the conditions of weak winds (almost in the absence of saltation processes) and strong heating of the land surface are given. These results show that the fine mineral dust aerosol (0.1-1 mu m) considerably contributes to the total aerosol content of the atmospheric surface layer under such conditions. The scaling of daytime mean size d distribution at a height of 2 m is approximated by dependence d(-mu), where mu changes from 4 to 6 for different years of measurements, in contrary to the law d-2 for fraction d > 1 mu m. Different compositions of aerosol particles at 0.1 < d < 1 mu m and d > 1 mu m, including multicomponent fractions (less than 1 mu m) may result in different probabilities of their integration and disintegration. It is hypothesized that the equilibrium distribution of submicron aerosol is a result of sequential disintegration of aerosol particles with a possibility for their reintegration. The simplest distribution approximations are given based on the Kolmogorov direct differential equation which is usually used in considering the Poisson distributions in equations for queuing systems.

Automated summary

The study conducted field measurements near the Caspian Sea and Aral Sea deserts in recent years, showing that fine mineral dust aerosols contribute significantly to the total aerosol content under specific conditions. The distribution of daytime mean size at a height of 2 m follows a certain pattern, and different compositions of aerosol particles at different sizes may lead to variations in integration and disintegration probabilities. The equilibrium distribution of submicron aerosols is hypothesized to be a result of sequential disintegration and reintegration of particles.