Balloon-borne observations of high aerosol concentrations near the summertime tropopause over the Tibetan Plateau

摘要

Vertical profiles of aerosols (radii ≥ 0.15 μm) were measured using a balloon-borne optical particle counter at Lhasa (29.4°N, 91.1°E, 3650 m a.s.l.), China in 1999. The measurements display occurrences of relatively high number concentrations (0.7-0.8 particles cm~(-3)) of sub-micron size aerosols with radii = 0.15-0.6 μm near the tropopause region (between about 130 and 70 hPa) in the Asian summer monsoon period. Size distributions of the observed aerosols are clearly different from those of cirrus clouds. The high number concentrations occurred inside the Tibetan anticyclone, suggesting that these were triggered by deep convection over the Tibetan Plateau. Convective transportation of lower tropospheric materials may affect atmospheric constituents near the tropopause region. In addition, the effects of adiabatic cooling and hydration associated with deep convection may also trigger enlargement of pre-existing and/or vertically-transported aqueous solution droplets (e.g., liquid sulfate particles) near the tropopause region. Enhancement of the aerosols should be considered in assessing the global/regional climate system and the geochemical cycle.