Organic contribution to sub-micron aerosol evolution over a boreal forest—a case study

Abstract

During the spring and summer of 1998 and spring of 1999 three major international campaigns have been performed at the SMEAR II Station (Station for Measuring Forest Ecosystem–Atmosphere Relations) in Hyytiälä, Finland. The measurements have been conducted as part of the BIOFOR programme, the objectives of which were to elucidate the main factors leading to nucleation and growth of new particles over forested regions. For typical nucleation events encountered in this environment, total particle concentration and surface area reduce rapidly due to mixing processes in the late morning prior to a nucleation event. After this reduction in pre-existing aerosol, ultra-fine particles (3–10 nm) appear, and grow rapidly (over several hours) towards accumulation mode sizes (>100 nm). Volatility measurements of new particle composition, once they have grown into accumulation mode sizes, illustrate a significant organic contribution to aerosol mass. Suggested contributors to this organic mass are pinic acid and/or cis-pinoic acid.