Influence of clouds on aerosol particle number concentrations in the upper troposphere

Abstract

This work investigates statistically the influence of clouds on aerosol particles in the upper troposphere, from the tropics to midlatitudes. More than 7500 particle concentration values, collected with the Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container, were analyzed for the occurrence of cloud contacts using backward trajectories and satellite images from the International Satellite Cloud Climatology Project. The majority of high‐altitude clouds over the Arabian Sea most likely contributed to the formation of new particles. At the contact, most clouds act as sink for Aitken and accumulation mode particles. However, as new particles grow these clouds act as indirect source for Aitken mode particles. A similar behavior was observed for clouds over the Caribbean. In contrast, no clear influence on nucleation mode particles was observed for most cloud contacts over the Middle East, southeastern Europe, and the midlatitude North Atlantic Ocean. However, in all three regions, the clouds act on average as sink for Aitken and accumulation mode particles. An analysis investigating the influence of the cloud contact duration showed that cloud contacts lasting 4 h or longer resulted in significantly higher number concentrations of nucleation and Aitken/accumulation mode particles than did short cloud contacts (1 h). This effect was observed over the Caribbean and southeastern Europe. Over the Arabian Sea, the Middle East, and the midlatitude North Atlantic Ocean, however, the duration of the cloud contact had no effect; it was only important whether a cloud contact had occurred.

Observing and understanding the Southeast Asian aerosol system by remote sensing: An initial review and analysis for the Seven Southeast Asian Studies (7SEAS) program

“…The remaining low particle counts may exist with high concentrations of precursor gases in a high actinic flux environment. Under such circumstances homogeneous nucleation of particles is theoretically possible, and has been observed (e.g., Perry and Hobbs, 1994;Hegg and Baker, 2009;Weigelt et al, 2009). Stohl et al (2007) in particular observed such behavior in SEA air transported to Europe.…”

Pollution events observed during CARIBIC flights in the upper troposphere between South China and the Philippines

“…Of all observations, 88% were conducted in the troposphere at PV values below 1.5 PVU (10 −6 K kg −1 m 2 s −1 ). All back-trajectories along the flight route were checked for cloud contact during the previous 2 days using a FORTRAN algorithm (Weigelt et al, 2009) overlaying back-trajectories and satellite cloud images from the International Satellite Cloud Climatology Project (IS-CCP, http://isccp.giss.nasa.gov/).…”

Atmospheric sub-3 nm particles at high altitudes

“…Our understanding on FT nucleation relies heavily on modelling studies that have concentrated on either binary water-sulphuric acid or ion-induced nucleation (Yu et al,al., 2008;Kazil and Lovejoy, 2004;Kanawade and Tripathi, 2006). In a small number of studies the number concentrations of ultrafine (>3-5 nm) aerosol particles have been measured in the FT, with main emphasis put on the upper parts of the FT (Clarke, 1993;de Reus et al, 2000;Twohy et al, 2002;Benson et al, 2008;Weigelt et al, 2009;Young et al, 2007). Very few measurements of ion cluster size distributions from this region are available (Arnold, 2006), and observations of neutral clusters are entirely lacking.…”