@article {70161, title = {Contributions of individual reactive biogenic volatile organic compounds to organic nitrates above a mixed forest}, journal = {Atmospheric Chemistry and Physics}, volume = {12}, year = {2012}, month = {2012}, pages = {10125 - 10143}, abstract = {. Biogenic volatile organic compounds (BVOCs) can react in the atmosphere to form organic nitrates, which serve as NOx (NO + NO2) reservoirs, impacting ozone and secondary organic aerosol production, the oxidative capacity of the atmosphere, and nitrogen availability to ecosystems. To examine the contributions of biogenic emissions and the formation and fate of organic nitrates in a forest environment, we simulated the oxidation of 57 individual BVOCs emitted from a rural mixed forest in northern Michigan. Key BVOCoxidant reactions were identified for future laboratory and field investigations into reaction rate constants, yields, and speciation of oxidation products. Of the total simulated organic nitrates, monoterpenes contributed \~{} 70 \% in the early morning at \~{} 12 m above the forest canopy when isoprene emissions were low. In the afternoon, when vertical mixing and isoprene nitrate production were highest, the simulated contribution of isoprene-derived organic nitrates was greater than 90 \% at all altitudes, with the concentration of secondary isoprene nitrates increasing with altitude. Notably, reaction of isoprene with NO3 leading to isoprene nitrate formation was found to be significant (\~{} 8 \% of primary organic nitrate production) during the daytime, and monoterpene reactions with NO3 were simulated to comprise up to \~{} 83 \% of primary organic nitrate production at night. Lastly, forest succession, wherein aspen trees are being replaced by pine and maple trees, was predicted to lead to increased afternoon concentrations of monoterpene-derived organic nitrates. This further underscores the need to understand the formation and fate of these species, which have different chemical pathways and oxidation products compared to isoprene-derived organic nitrates and can lead to secondary organic aerosol formation.}, keywords = {TERPENES}, doi = {10.5194/acp-12-10125-2012}, author = {Pratt, K. A. and Mielke, L. H. and Shepson, P. B. and Bryan, A. M. and Steiner, A. L. and Ortega, J. and Daly, R. and Helmig, D. and Vogel, C. S. and Griffith, S. and Dusanter, S. and Stevens, P. S. and Alaghmand, M.} } @article {70164, title = {In-canopy gas-phase chemistry during CABINEX 2009: sensitivity of a 1-D canopy model to vertical mixing and isoprene chemistry}, journal = {Atmospheric Chemistry and Physics}, volume = {12}, year = {2012}, note = {PROPHET}, month = {2012}, pages = {8829 - 8849}, publisher = {EGU Journals}, type = {CABINEX}, abstract = {Vegetation emits large quantities of biogenic volatile organic compounds (BVOC). At remote sites, these compounds are the dominant precursors to ozone and secondary organic aerosol (SOA) production, yet current field studies show that atmospheric models have difficulty in capturing the observed HOx cycle and concentrations of BVOC oxidation products. In this manuscript, we simulate BVOC chemistry within a forest canopy using a one-dimensional canopy-chemistry model (Canopy Atmospheric CHemistry Emission model; CACHE) for a mixed deciduous forest in northern Michigan during the CABINEX 2009 campaign. We find that the base-case model, using fully-parameterized mixing and the simplified biogenic chemistry of the Regional Atmospheric Chemistry Model (RACM), underestimates daytime in-canopy vertical mixing by 50{\textendash}70\% and by an order of magnitude at night, leading to discrepancies in the diurnal evolution of HOx, BVOC, and BVOC oxidation products. Implementing observed micrometeorological data from above and within the canopy substantially improves the diurnal cycle of modeled BVOC, particularly at the end of the day, and also improves the observation-model agreement for some BVOC oxidation products and OH reactivity. We compare the RACM mechanism to a version that includes the Mainz isoprene mechanism (RACM-MIM) to test the model sensitivity to enhanced isoprene degradation. RACM-MIM simulates higher concentrations of both primary BVOC (isoprene and monoterpenes) and oxidation products (HCHO, MACR+MVK) compared with RACM simulations. Additionally, the revised mechanism alters the OH concentrations and increases HO2. These changes generally improve agreement with HOx observations yet overestimate BVOC oxidation products, indicating that this isoprene mechanism does not improve the representation of local chemistry at the site. Overall, the revised mechanism yields smaller changes in BVOC and BVOC oxidation product concentrations and gradients than improving the parameterization of vertical mixing with observations, suggesting that uncertainties in vertical mixing parameterizations are an important component in understanding observed BVOC chemistry.}, keywords = {VEGETATION}, doi = {10.5194/acp-12-8829-2012}, author = {Bryan, A. M. and Bertman, S. B. and Carroll, M. A. and Dusanter, S. and Edwards, G. D. and Forkel, R. and Griffith, S. and Guenther, A. B. and Hansen, R. F. and Helmig, D. and Jobson, B. T. and Keutsch, F. N. and Lefer, B. L. and Pressley, S. N. and Shepson, P. B. and Stevens, P. S. and Steiner, A. L.} }