A parameterization of dust concentration (PM₁₀) of dust events observed at Erdene in Mongolia using the monitored tower data

Abstract

Hourly mean time series of dust concentration (PM₁₀) measured at 3m high and a sonic-anemometer measured momentum and kinematic heat fluxes at 8m high above the surface have been obtained from a 20-m monitoring tower located at Erdene in the Asian dust source region of Mongolia for years of 2009 and 2010. These time series were used to identify dust events and to develop optimal regression equations for the dust concentration of dust events with the friction velocity (u(*)) and the convective velocity scale (w(*)). In total, 68 dust events were identified in 2009 (except for November) and 43 dust events for the period from March to August in 2010. The duration of each dust event ranged from 3-29 h in 2009 and 5-35 h in 2010. The maximum hourly mean dust concentration of the dust event was found to be 4,107 μg m⁻³ in May in 2009 and 4,708 μg m⁻³ in March in 2010 while a minimum of 251 μg m⁻³ in August in 2009 and 662 μg m⁻³ in June in 2010. The optimal regression equation for the dust concentration (C) of dust events was found to have the form of log C=a+b(u(*)+cw(*))(n), where a, b, c and n are constants that vary month to month. The convective velocity scale (w(*)) that has not been taken into account in most dust modelings was found to enhance the dust concentration of dust events during the cold period from December to March when the soil temperature was below the freezing level for both the stable (w(*)<0) and unstable (w(*)>0) stratifications, whereas the convective velocity caused a reduction in the dust concentrations during the warm period from April to October, suggesting the importance of the convective velocity to estimate dust concentration of dust events.