Directed by Dr. William L. Chameides
Abstract. Two problems related to atmospheric aerosols were treated: a) the formation of H2SO4-H2O particles under background tropospheric conditions and b) aerosol interactions in the wake of aircraft and the dependence of contrails on engine sulfur emissions.
The data collected during the Pacific Exploratory Mission Phase B (PEM-West B) for February-March, 1994 were used to constrain a numerical model that calculates local concentrations of gaseous H2SO4, rates of homogeneous nucleation, and concentrations of newly-formed, nm-sized H2SO4-H2O particles. The largest nucleation rates were calculated for the flights over the temperate latitudes (L > 300 N). Within these latitudes, homogeneous nucleation rates averaged about 103-104 particles cm-3 s-1 in the BL and decreased slightly with altitude. Significantly smaller nucleation rates were calculated for the tropical (L < 200 N) and sub-tropical (200 N < L < 300 N) regions. The relatively large nucleation rates calculated for the temperate latitudes could be attributed to the low temperatures and high SO2 concentrations encountered in this region. For the data from the tropical and subtropical flights, little or no homogeneous nucleation was calculated for the average conditions encountered in the boundary layer (BL) and mid-troposphere (MT). Instead, significant nucleation was limited to either the upper troposphere (UT) or to short-lived bursts generally characterized by high relative humidity and low aerosol surface density. The strongest nucleation bursts were associated with high concentrations of SO2, as a result of pollution from Asia.
For the second problem, an aircraft plume model was applied to investigate the effects of engine emissions on the characteristics of contrails. The model simulated the formation and growth H2SO4-H2O particles and the growth of activated soot particles. The results indicated that: 1) For a given initial concentration of soot particles and ambient conditions, the condensed water content increases with the emission index of SO2; 2) Due to interactions of soot particles with H2SO4-H2O aerosol and gaseous sulfur species, sulfate is added to the soot surface. As a result, the contrail particle size after evaporation of water increases with the sulfur content of the fuel; and 3) For high sulfur content, visible contrails tend to form at temperatures higher than predicted by Appleman's theory.
Keywords/Free Terms: nucleation, tropospheric aerosols, soot particles, sulfur emissions, aircraft contrail.
Andronache, C., and W. L. Chameides, Interactions between sulfur and soot emissions from aircraft and their role in contrail formation 2. Development, J. Geophys. Res., 103, 10,787-10802, 1998. Abstract [html]
Andronache, C., W. L. Chameides, D. D. Davis, B. E. Anderson, R. F. Pueschel, A. R. Bandy, D. C. Thornton, R. W. Talbot, P. Kasibhatla, and C. S. Kiang, Gas-to-particle conversion of tropospheric sulfur as estimated from observations in the western North Pacific during PEM-West B, J. Geophys. Res., 102, 28,511-28,538, 1997. Abstract [html]
Andronache, C., and W. L. Chameides, Interactions between sulfur and soot emissions from aircraft and their role in contrail formation 1. Nucleation, J. Geophys. Res., 102, 21,443-21,451, 1997. Abstract [html]