Isoprene suppression of new particle formation in a mixed deciduous forest V. P. Kanawade1, B. T. Jobson2, A. B. Guenther3, M. E. Erupe1, S. N. Pressley2, S. N. Tripathi4, and S.-H. Lee1 1Department of Chemistry and Biochemistry, Kent State University, Kent, OH 44242, USA 2Department of Civil and Environmental Engineering, Washington State University, WA 99164, USA 3National Center for Atmospheric Research, Atmospheric Chemistry Division, Boulder, CO 80307, USA 4Department of Civil Engineering and Center for Environmental Engineering and Science, Indian Institute of Technology, Kanpur 208016, Uttar Pradesh, India
Abstract. Production of new particles over forests is an important source of cloud
condensation nuclei that can affect climate. While such particle formation
events have been widely observed, their formation mechanisms over forests
are poorly understood. Our observations made in a mixed deciduous forest
with large isoprene emissions during the summer displayed a surprisingly
rare occurrence of new particle formation (NPF). Typically, NPF events occur
around noon but no NPF events were observed during the 5 weeks of
measurements. The exceptions were two evening ultrafine particle events.
During the day, sulfuric acid concentrations were in the 106 cm−3
range with very low preexisting aerosol particles, a favorable condition for
NPF to occur even during the summer. The ratio of emitted isoprene carbon to
monoterpene carbon at this site was similar to that in Amazon rainforests
(ratio >10), where NPF events are also very rare, compared with a ratio
<0.5 in Finland boreal forests, where NPF events are frequent. Our results
suggest that large isoprene emissions can suppress NPF formation in forests
although the underlying mechanism for the suppression is unclear. The two
evening ultrafine particle events were associated with the transported
anthropogenic sulfur plumes and ultrafine particles were likely formed via
ion-induced nucleation. Changes in landcover and environmental conditions
could modify the isoprene suppression of NPF in some forest regions
resulting in a radiative forcing that could have influence on the climate.
Citation: Kanawade, V. P., Jobson, B. T., Guenther, A. B., Erupe, M. E., Pressley, S. N., Tripathi, S. N., and Lee, S.-H.: Isoprene suppression of new particle formation in a mixed deciduous forest, Atmos. Chem. Phys., 11, 6013-6027, doi:10.5194/acp-11-6013-2011, 2011.