Metastable phases in polar stratospheric aerosols
- Harvard Univ., Cambridge, MA (United States)
- Center for Chemical and Environmental Physics, Billerica, MA (United States)
Phase changes in stratospheric aerosols were studied by cooling a droplet of sulfuric acid (H{sub 2}SO{sub 4}) in the presence of nitric acid (HNO{sub 3}) and water vapor. A sequence of solid phases was observed to form that followed Ostwald`s rule for phase nucleation. For stratospheric partial pressures at temperatures between 193 and 195 kelvin, a metastable ternary H{sub 2}SO{sub 4}-HNO{sub 3} hydrate, H{sub 2}SO{sub 4} {center_dot} HNO{sub 3} {center_dot} 5H{sub 2}O, formed in coexistence with binary H{sub 2}SO{sub 4} {center_dot} kH{sub 2}O hydrates (k = 2, 3, and 4) and then transformed to nitric acid dihydrate, HNO{sub 3} {center_dot} 2H{sub 2}O, within a few hours. Metastable HNO{sub 3} {center_dot} 2H{sub 2}O always formed before stable nitric acid trihydrate, HNO{sub 3} {center_dot} 3H{sub 2}O, under stratospheric conditions and persisted for long periods. The formation of metastable phases provides a mechanism for different particle growth and sedimentation of HNO{sub 3} from the polar winter stratosphere. 28 refs., 15 figs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 56814
- Journal Information:
- Science, Journal Name: Science Journal Issue: 5196 Vol. 267; ISSN SCIEAS; ISSN 0036-8075
- Country of Publication:
- United States
- Language:
- English
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