1Department of Chemistry, University of California Berkeley, Berkeley, CA, USA
2National Center for Atmospheric Research, Earth Observing Laboratory, Boulder, CO, USA
3Graduate School of Oceanography, University of Rhode Island, Narragansett, RI, USA
4Climate Change Research Institute, University of New Hampshire, Durham, NH, USA
5Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA
6Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
7Division of Environmental Science and Engineering, California Institute of Technology, Pasadena, CA, USA
8Department of Chemistry, University of California Irvine, Irvine, CA, USA
9Department of Meteorology, Pennsylvania State University, University Park, PA, USA
10NASA Ames Research Center, Moffett Field, CA, USA
11Department of Earth and Planetary Sciences, University of California Berkeley, Berkeley, CA, USA
*now at: Department of Atmospheric Sciences, University of Washington, Seattle, WA, USA
Received: 16 May 2008 – Published in Atmos. Chem. Phys. Discuss.: 24 Jun 2008 – Published: 23 Feb 2009
Abstract. Formation of isoprene nitrates (INs) is an important free radical chain termination step ending production of ozone and possibly affecting formation of secondary organic aerosol. Isoprene nitrates also represent a potentially large, unmeasured contribution to OH reactivity and are a major pathway for the removal of nitrogen oxides from the atmosphere. Current assessments indicate that formation rates of isoprene nitrates are uncertain to a factor of 2–3 and the subsequent fate of isoprene nitrates remains largely unconstrained by laboratory, field or modeling studies. Measurements of total alkyl and multifunctional nitrates (ΣANs), NO2, total peroxy nitrates (ΣPNs), HNO3, CH2O, isoprene and other VOC were obtained from the NASA DC-8 aircraft during summer 2004 over the continental US during the INTEX-NA campaign. These observations represent the first characterization of ΣANs over a wide range of land surface types and in the lower free troposphere. ΣANs were a significant, 12–20%, fraction of NOy throughout the experimental domain and ΣANs were more abundant when isoprene was high. We use the observed hydrocarbon species to calculate the relative contributions of ΣAN precursors to their production. These calculations indicate that isoprene represents at least three quarters of the ΣAN source in the summertime continental boundary layer of the US. An observed correlation between ΣANs and CH2O is used to place constraints on nitrate yields from isoprene oxidation, atmospheric lifetimes of the resulting nitrates and recycling efficiencies of nitrates during subsequent oxidation. We find reasonable fits to the data using sets of production rates, lifetimes and recycling efficiencies of INs as follows (4.4%, 16 h, 97%), (8%, 2.5 h, 79%) and (12%, 95 min, 67%). The analysis indicates that the lifetime of ΣANs as a pool of compounds is considerably longer than the lifetime of the individual isoprene nitrates to reaction with OH, implying that the organic nitrate functionality is at least partially maintained through a second oxidation cycle.
Perring, A. E., Bertram, T. H., Wooldridge, P. J., Fried, A., Heikes, B. G., Dibb, J., Crounse, J. D., Wennberg, P. O., Blake, N. J., Blake, D. R., Brune, W. H., Singh, H. B., and Cohen, R. C.: Airborne observations of total RONO2: new constraints on the yield and lifetime of isoprene nitrates, Atmos. Chem. Phys., 9, 1451-1463, doi:10.5194/acp-9-1451-2009, 2009.