Size distribution and seasonal variation of atmospheric cellulose

Atmospheric cellulose is a main constituent of the insoluble organic aerosol and a “macrotracer” for plant debris. A time series of the cellulose concentration at a downtown site in Vienna showed a maximum concentration during fall and a secondary maximum during spring. The fall maximum appears to be associated with leaf litter production, the spring maximum with increased biological activity involving repulsion of cellulose-containing particles, e.g. seed production. The grand average of the time series over 9 months was 0.374 μgm−3 cellulose, respectively, 0.75 μgm−3 plant debris. Compared to an annual average of 5.7 μgm−3 organic carbon as observed at a Vienna downtown site it becomes clear that plant debris is a major contributor to the organic aerosol and has to be considered in source attribution studies. Simultaneous measurements at the downtown and a suburban site indicated that particulate cellulose is obviously not produced within the city in notable amounts, at least during the campaign in December. Size distribution measurements with impactors showed the unexpected result that “fine aerosol” size particles (0.1–1.6 μm aerodynamic diameter) contained 0.7% “free cellulose” on a mass basis, forming a wettable, but insoluble part of the accumulation mode aerosol.