Aerosol Production in a Mixed Deciduous/Coniferous Forest

Aerosols are of fundamental concern because of their impacts on air quality, human health and radiative forcing. Recent studies have focused on secondary organic aerosol (SOA) production due to oxidation of volatile organic compounds (VOCs), and more importantly biogenic-VOCs (BVOCs), in particular, isoprene. However, the SOA precursors are not well understood because the mechanisms have shown that isoprene oxidation can contribute to aerosol production through multiple generation oxidation products. For terpenes, it is more likely that primary or secondary oxidation products lead to particle formation. In the present study, we measured the aerosol size distribution, along with O3, HOx, NOx, NOy and BVOCs, in a mixed deciduous forest that is undergoing successional transition to a conifer-dominated species mix. This study was conducted in a rural forest environment in northern Michigan as a part of the summer 2008 PROPHET campaign at the University of Michigan Biological Station (UMBS). We examine here the potential BVOC contribution to aerosol formation. A TSI, inc. Scanning Mobility Particle Sizer (SMPS) was used to measure aerosol number density in the size range, 15 nm < x < 711 nm and a Proton Transfer Reaction - Linear Ion Trap (PTR-LIT) mass spectrometer for quantifying isoprene and other BVOCs, including methyl vinyl ketone and methacrolein, and total monoterpenes. Preliminary results show periods of new particle production. Here we use a unique set of BVOC, HOx, NOx, NOy, O3 and meteorological data to examine conditions leading to new particle production.