HR: 09:45h
AN: A31B-08    [PDF]
TI: Nitric acid depressions in and near midlatitude cirrus clouds during TRACE-P
AU: * Zondlo, M A
EM: mzondlo@swsciences.com
AF: Southwest Sciences, Inc., 1570 Pacheco Street, Suite E-11, Santa Fe, NM 87505 United States
AU: Cantrell, C A
EM:
AF: NCAR/ACD, 1850 Table Mesa Drive P.O. Box 3000, Boulder, CO 80305 United States
AU: Clarke, A
EM:
AF: University of Hawaii, 2525 Correa Road, HIG 350, Honolulu, HI 96822 United States
AU: Kosciuch, E
EM:
AF: NCAR/ACD, 1850 Table Mesa Drive P.O. Box 3000, Boulder, CO 80305 United States
AU: Mauldin, R L
EM:
AF: NCAR/ACD, 1850 Table Mesa Drive P.O. Box 3000, Boulder, CO 80305 United States
AU: Eisele, F L
EM:
AF: NCAR/ACD, 1850 Table Mesa Drive P.O. Box 3000, Boulder, CO 80305 United States
AB: Cirrus cloud ice particles have been implicated in scavenging a wide variety soluble and semisoluble species. Species removed by an ice surface can undergo a number of significant processes including heterogeneous reactions with other adsorbed species, vertical redistribution in the troposphere from sedimenting particles, or modifying the microphysical properties of the ice particle. Nitric acid (HNO3) has been shown in the laboratory to readily adsorb onto ice surfaces, and modeling studies suggest significant perturbations to its distribution can result. Unfortunately, field observations of HNO3 within and near cirrus clouds have shown mixed and sometimes contradictory results. The NASA P-3B aircraft sampled numerous upper tropospheric, mid-latitude ice clouds during Flight 24 of the NASA TRACE-P field experiment. In contrast to tropical cirrus clouds, the cirrus ice clouds sampled by the P-3B were at warmer temperatures of -17 to -32 degrees Celsius and at pressures of 365-436 mb. The clouds' origins ranged from jet stream induced cirrostratus clouds to convectively-induced cirrus anvils. Nitric acid levels decreased 60-70 pptv (35-60%) within the clouds compared to areas just outside of it. Slight asymmetries in the HNO3 profiles around the cloud were noted, with the lee or downwind sides of clouds containing more gradual returns from inside cloud levels to "background" levels, potentially due to greater mixing as the cloud evaporated. If HNO3 removed inside the cloud were distributed evenly onto ice surfaces, approximately one tenth of a monolayer of HNO3 was adsorbed onto ice (based on estimates of ice surface area density of 5000 microns squared per cubic centimeter). The incorporation of HNO3 into existing liquid quaternary NH3/H2SO4/HNO3/H2O aerosols within the cloud could also be important due to the sampling location over central North America where elevated NH3 emissions exist. The midlatitude HNO3/cirrus cases observed on the P-3B will be contrasted to liquid water clouds sampled elsewhere during TRACE-P (only slight depressions observed), recent field results of tropical cirrus clouds, and laboratory and modeling studies.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
DE: 0322 Constituent sources and sinks
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting