Aircraft Measurements on Properties of Aerosols over the Central and Eastern Qinghai-Tibet Plateau

Abstract

The central and eastern Qinghai-Tibet Plateau is the birthplace of the Yellow River, the Yangtze River and the Lancang River. It is also a climate change sensitive area and a key ecological protection area. Based on observations of 11 sorties conducted in summer and autumn of 2011 and 2013, the vertical distribution of aerosol number concentration and number spectrum at Golmud, and the transport characteristics as well as the horizontal distribution and nucleation characteristics of aerosol number concentration and cloud condensation nuclei (CCN) number concentration at mid-altitude of the central and eastern Plateau are analyzed. The results indicate that the vertical and horizontal distributions of aerosol number concentration (Na) and volume diameter (Dv) in the central and eastern Qinghai-Tibet Plateau are significantly different due to the influence of weather system, topography, and surface characteristics. The aerosol number concentration is high in the northwest and low in the southeast. The volume diameter is large in the lower layer, small in the upper layer, and there are dust layers in the middle and upper layers. Precipitation has clear effects on low-level aerosols when east wind prevails at Golmud, and the aerosol number concentration and volume diameter are significantly reduced. At the same time, due to plateau gale or convection, sand and dust layers also form at the middle and upper altitudes of 6.2 km and 7.2-7.4 km. The aerosol volume diameter of the lower layer is 1.8 μm mainly when westerly wind prevails, the number concentration increases with the increase of height and wind speed, the variation of aerosol volume diameter is small, and the sand and dust layer also appears at 6.2 km altitude. Under the influence of different weather systems over 6.5 km altitude, submicron particles are imported, and the number concentration even reaches 5×103 cm-3. Moreover, the aerosol number concentration and particle size imported at about 8.0 km altitude when east wind prevails are denser and smaller than those imported when west wind prevails, and the vertical distribution of spectrum also shows the same characteristics. The measurement of cloud condensation nuclei number concentration (Nccn) with different supersaturation shows that the mean nucleation rate is generally 1%-16%, except that the nucleation rate below 6 km altitude at Golmud is 21%-47%, and the nucleation rate at 6.0-8.5 km altitude is generally low. When the aerosol number concentration increases, the nucleation rate decreases significantly, and its value is relatively high with the supersaturation being 1%-2%, in the layer between -15 and -5℃ or the particle size of 1-3 μm.

Keywords

• aircraft measurement
• aerosol
• nucleation