wind of urban areas (University of Chicago). 

 These particles are associated with the devel- 

 opment of a stable haze (University of Chicago) 

 which forms during serious air pollution epi- 

 sodes and results in a widespread restriction of 

 visibility (University of Wyoming) and a reduc- 

 tion in solar radiation reaching the surface 

 (Center for Environment and Man). 

 Unusually high concentrations of very large 

 CCN are also observed downwind of cities 

 (University of Chicago). The modified CCN 

 concentrations result in modified cloud dro- 

 plet populations which extend several urban 

 diameters downstream (University of Chica- 

 go). Although the bases of urban clouds are 

 usually higher than surrounding rural clouds 

 (Illinois State Water Survey), radar detection 

 of the first precipitation echoes occurs lower 

 in the urban clouds (University of Chicago), 

 presumably from the urban-industrial CCN, 

 although the observations connecting these 

 effects remain to be made. 

 Boundary layer dynamics. The altered surface 

 features in an urban area cause a reduction in eva- 

 potranspiration and an alteration of surface heat 

 storage, resulting in a warm, dry urban boundary 

 layer (University of Wyoming). This effect is com- 

 bined with alterations in surface roughness fea- 

 tures to change the airflow characteristics of the 

 urban boundary layer. Combined observations of 

 the airflow and thermal structure of the urban 

 boundary layer using instrumented research air- 

 craft (University of Wyoming), dual Doppler radar 

 (National Oceanic and Atmospheric Administra- 

 tion (NOAA/WPD), and balloon soundings 

 (Illinois State Water Survey) provide new insights 

 into thermal perturbing influences on boundary 

 layer airflow. Convergence and divergence pat- 

 terns are driven by warm (heat island) and cold air 

 anomalies (University of Wyoming). During the 

 daytime, the convergence patterns may take the 

 form of a vertical roll circulation (NOAA/WPL). 

 The net boundary layer convergence into the urban 

 heat island approaches 10-4 sec"' and may result in 

 the local deepening of the boundary layer by sev- 

 eral hundred meters (University of Wyoming). At 

 night, the convergence into the city appears as in- 

 termittent flow, and the urban influences produce 

 anomalous low-level maxima in the vertical wind 

 profiles (Illinois State Water Survey). 



Current and Future Research 

 Emphasis 



The five most interesting agency projects involv- 

 ing basic research which are currently in progress 

 are: 



"Enhancing Biological Production of Ammo- 

 nia from Atmospheric Nitrogen and Soil Ni- 

 trate," J. M. Lyons, University of California, 

 Davis. Dr. Raymond C. Valentine, from the 

 University of California at Davis, has been an 

 active investigator in the area of biological 

 nitrogen fixation for many years. During this 

 time, he received funding from NSF via its 

 basic research directorate. Biological and 

 Medical Sciences (BMS), now Biological, 

 Behavioral, and Social Science's (BBS), to 

 discover new facts and phenomena on the 

 genetics of nitrogen-fixing organisms. A most 

 important contribution was the observation 

 that mutants of bacteria were able to excrete 

 ammonia into the environment. As his re- 

 search and interests became more problem- 

 oriented, he sought RANN support for his 

 work. 



Specifically, his initial proposal in late 1974 

 dealt with the anaerobic, free-living, nitrogen- 

 fixing bacteria, Klebsiella pneumoniae, and 

 the objective of his research was to construct 

 more efficient ammonia-excreting mutants and 

 to determine the optimum physiological con- 

 ditions for growth and nitrogen fixation. Dr. 

 Valentine's most recent publication (first an- 

 nounced at the 1977 National Academy of 

 Sciences (NAS) forum on recombinant DNA 

 research) details the specific requirements of 

 these microbes as well as the implications of 

 this research. Recently, Dr. Valentine has 

 also generated a broader program in biological 

 nitrogen fixation with his colleagues at Davis. 

 This is a multicomponent program (the princi- 

 pal investigator is J. M. Lyons), the overall 

 goal of which is to utilize solar energy to en- 

 hance the production of ammonia from atmos- 

 pheric nitrogen or soil nitrate by biological 

 systems. Major objectives are: 



(1) Enhancing the nitrogen-fixing capability 

 of natural bacteria that possess this char- 

 acteristic by genetically constructing su- 

 perior mutants 



(2) Increasing the efficiency of symbiotic ni- 

 trogen fixation in legumes by identifying 

 naturally occurring and genetically con- 

 structed variants of the Rhizobium bacte- 

 ria and the host legume 



(3) Maximizing nitrogen fixation in cereals, 

 especially rice, through the use of the 

 symbiotic fern Azolla and blue green al- 

 gae 



(4) Conserving fixed nitrate nitrogen by gen- 

 etically modifying typical soil microorgan- 

 isms and by identifying and controlling 



NATIONAL SCIENCE FOUNDATION 21 9 



