Global Distribution and Sources of Volatile And Nonvolatile Aerosol in the Remote Troposphere

 

Hanwant B. Singh, W. Viezee, Y. Chen, A. Tabazadeh, R. Pueschel

Airborne measurements of aerosol (condensation nuclei, CN) and selected trace gases made over areas of the North Atlantic Ocean during SONEX (October/November 1997), the south tropical Pacific Ocean during PEM-Tropics A (September/October 1996), and PEM-Tropics B (March/April 1999) have been analyzed. The emphasis is on interpreting variations in the number densities of fine (>17 nm) and ultrafine (>8 nm) aerosol in the upper troposphere (8-12 km). These data suggest that large number densities of highly volatile CN (104-105 cm-3) are present in the upper troposphere, and particularly over the tropical/subtropical region. CN number densities in all regions are largest when the atmosphere is devoid of non-volatile particles. Through marine convection and long-distance horizontal transport, volatile CN originating from the tropical/subtropical regions can frequently impact the abundance of aerosol in the middle and upper troposphere at mid-to-high latitudes. Nonvolatile aerosol behave in a manner similar to tracers of combustion (CO) and photochemical pollution (PAN), implying a continental pollution source from industrial emissions or biomass burning. In the upper troposphere, we find that volatile and nonvolatile aerosol number densities are inversely correlated. Results from an aerosol microphysical model suggest that the coagulation of fine volatile particles with fewer but larger nonvolatile particles, of principally anthropogenic origin, is one possible explanation for this relationship. In some instances the larger nonvolatile particles may also directly remove precursors ( e. g. H2SO4) and effectively stop nucleation.

 

Collaborators: B. Anderson, M. Avery, NASA Langley Research Center; P. Hamill, San Jose State University; H. Fuelberg and J. R. Hannan, Florida State University, Tallahassee

Point of Contact: Hanwant B. Singh, 650/604-6769, hsingh@mail.arc.nasa.gov

Hanwant Singh web site