Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 9 21 2009 10.5194/acp-9-8283-2009 http://www.atmos-chem-phys.net/9/8283/2009/ http://www.atmos-chem-phys.net/9/8283/2009/acp-9-8283-2009.html http://www.atmos-chem-phys.net/9/8283/2009/acp-9-8283-2009.pdf 8283 8308 2009-11-03 Observations of heterogeneous reactions between Asian pollution and mineral dust over the Eastern North Pacific during INTEX-B C. S. McNaughton csmcnaug@hawaii.edu A. D. Clarke V. Kapustin Y. Shinozuka S. G. Howell B. E. Anderson E. Winstead J. Dibb E. Scheuer R. C. Cohen P. Wooldridge A. Perring L. G. Huey S. Kim J. L. Jimenez E. J. Dunlea P. F. DeCarlo P. O. Wennberg J. D. Crounse A. J. Weinheimer F. Flocke School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, 96822 HI, USA NASA Langley Research Center, Hampton, 23665 VA, USA University of New Hampshire, Durham, 03824 NH, USA University of California Berkeley, Berkeley, 94720 CA, USA Georgia Institute of Technology, Atlanta, 30332 GA, USA Cooperative Institute for Research in Environmental Sciences (CIRES) and University of Colorado, Boulder, 80309 CO, USA California Institute of Technology, Pasadena, 91125 CA, USA National Center for Atmospheric Research, Boulder, 80307 CO, USA now at: NASA Ames Research Center, Moffett Field, 94035 CA, USA now at: Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland In-situ airborne measurements of trace gases, aerosol size distributions, chemistry and optical properties were conducted over Mexico and the Eastern North Pacific during MILAGRO and INTEX-B. Heterogeneous reactions between secondary aerosol precursor gases and mineral dust lead to sequestration of sulfur, nitrogen and chlorine in the supermicrometer particulate size range. <br><br> Simultaneous measurements of aerosol size distributions and weak-acid soluble calcium result in an estimate of 11 wt% of CaCO₃ for Asian dust. During transport across the North Pacific, ~5–30% of the CaCO₃ is converted to CaSO₄ or Ca(NO₃)₂ with an additional ~4% consumed through reactions with HCl. The 1996 to 2008 record from the Mauna Loa Observatory confirm these findings, indicating that, on average, 19% of the CaCO₃ has reacted to form CaSO₄ and 7% has reacted to form Ca(NO₃)₂ and ~2% has reacted with HCl. In the nitrogen-oxide rich boundary layer near Mexico City up to 30% of the CaCO₃ has reacted to form Ca(NO₃)₂ while an additional 8% has reacted with HCl. <br><br> These heterogeneous reactions can result in a ~3% increase in dust solubility which has an insignificant effect on their optical properties compared to their variability in-situ. However, competition between supermicrometer dust and submicrometer primary aerosol for condensing secondary aerosol species led to a 25% smaller number median diameter for the accumulation mode aerosol. A 10–25% reduction of accumulation mode number median diameter results in a 30–70% reduction in submicrometer light scattering at relative humidities in the 80–95% range. At 80% RH submicrometer light scattering is only reduced ~3% due to a higher mass fraction of hydrophobic refractory components in the dust-affected accumulation mode aerosol. 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