CONTENTS 



Forced air-flow impactors 



Adhesives 

 Thermal precipitation 

 Electrostatic precipitation . 

 Comparison of methods 



IX The Air-Spora near the Earth's Surface 

 Composition of the air-spora 

 Taxonomic groups needing study in the air-spora 

 Miquel's work on bacteria and moulds 



Effect of rain .... 



Diurnal periodicity 



Relative numbers of bacteria and moulds 

 Recent study of fungi and pollen 



The air-spora at 2 metres above ground-level 



The air-spora at other heights near the ground 



Diurnal periodicit}' of fine-weather spora 



Seasonal changes 



Effect of localit}' 



Effect of weather 



Biotic factors 

 Marine air 



The air of polar regions 

 The origin of the air-spora 



X The Upper-air Spora 

 Vertical diffusion 



Ground stations at different altitudes above sea-level 



The role of turbulence . 

 Early studies of the upper air 



Sampling from balloons . 



The stratosphere . 



Sampling from aeroplanes 



Spores of green plants in the lower troposphere 

 McGill Universit}" studies 



Flights over the Arctic 



Microbiology of air masses over northern Canada 



Air masses over Montreal 



Air masses over the North Atlantic Ocean 



\'ertical gradient over the ocean 

 Summary ..... 



XI Deposition in Rain, Snow, and Hail 

 Rain ..... 

 Snow ..... 

 Hail 



XII The Air-Spora of Enclosed Spaces 

 Die-away of concentration . 

 Spore movement in convection currents 



ix 



