Nucleation in the equatorial free troposphere: Favorable environments during PEM-Tropics

Clarke, AD Eisele, F Kapustin, VN Moore, K Tanner, D Mauldin, L Litchy, M Lienert, B Carroll, MA Albercook, G

Ad. Clarke et al., Nucleation in the equatorial free troposphere: Favorable environments during PEM-Tropics, J GEO RES-A, 104(D5), 1999, pp. 5735-5744

32

INGLESE

Article

Earth Sciences

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES → ACNP

104

D5

1999

5735 - 5744

ISI

A combination of aerosol and gas phase instrumentation was employed aboard the NASA-P3B as part of the Pacific Exploratory Mission-Tropics (PEM-T) in the eastern equatorial Pacific during August-October 1996. Recent particle production was found in cloud-processed air over extended regions aloft (6- 8 km). These were clearly associated with clean marine air lofted by deep c onvection and scavenged of most aerosol mass in the Intertropical Convergen ce Zone (ITCZ) and in more aged cloud-scavenged air influenced by a distant continental combustion near the South Pacific Convergence Zone (SPCZ). Rec ent particle production was evident in regions where sulfuric acid concentr ations were about 0.5 to 1 x 10(7) molecules cm(-3), when surface areas wer e near or below 5 mu m(2) cm(-3), and when relative humidity (RH) was eleva ted over adjacent regions. In regions of recent particle production, the ca lculated critical sulfuric acid concentrations, based upon classical binary nucleation theory and corrected for in situ conditions near cloud, were ge nerally consistent with nearby observed sulfuric acid concentrations. This indicates that classical binary nucleation theory and natural sources of su lfuric acid can account for nucleation in the near-cloud environment. Data from six equatorial flights between 20 degrees N and 20 degrees S demonstra te that this process populates extensive regions of the equatorial free tro posphere with new particles. Vertical profiles suggest that nucleation, sub sidence, and mixing into the MBL can supply the MBL with new aerosol.