Chemical and optical properties of 2003 Siberian forest fire smoke observed at the summit of Mt. Fuji, Japan

Abstract

Boreal forest fires are one of the major emission sources of trace atmospheric constituents in mid and high latitudes in the Northern Hemisphere. From late May through early June 2003, dense smoke aerosols that originated from large forest fires in Siberia were monitored on the summit of Mt. Fuji (3776 m msl.), Japan, a free‐tropospheric height monitoring site where measurements of atmospheric chemistry were briefly intensified during a research project called Atmospheric Environmental Impact of Aerosols in East Asia (AIE). Inside a smoke layer, concentrations of black carbon (BC) measured by an Aethalometer exceeded 1900 ng m−3 with a concurrent increase of carbon monoxide mixing ratio. The slope of a BC/CO regression line was steeper than those obtained in other studies using measurements from lower‐altitude ground monitoring stations, suggesting minimal wet removal processes. The smoke aerosols contained high levels of n‐alkanes of high molecular weight and indicated high carbon preference indices. The time series of CO and O3 mixing ratios indicated a double‐layered vertical structure in which a high O3 mixing ratio layer lay on top of a smoke layer. The wavelength dependence of the absorption coefficient of the smoke showed a slope much steeper than that measured in urban influenced measurements. The higher absorption in the shorter wavelengths was consistent with an abundance of organic species within the smoke.