398 



Plant as an Index of Smoke Pollution 



A chemical analysis of the plant will give exceedingly useful informa- 

 tion as to the amount of smoke pollution in the district in which it was 

 grown. In this connection the following analyses of the deposits on 

 aucuba leaves carried out by the Air Analysis Committee of the Field 

 Naturalists' Society of Manchester in the winter of 1890-91 are of 

 interest. 



Deposit on Aucuba Leaves. 



In milligrams per square metre of leaf surface. 



Date 



1890 



Dec. 14 



13 



16 



14 



14 



13 



1891 



Jan. 17 



9.9 



Locality 



Alexandra Park 

 Owens College 

 Hulrne 

 Harpurhey 

 Infirmary 

 Albert Square 



Peel Park 

 Queen's Park 



Description 



Surburban 



Urban 



Surburban 



Solid 

 deposit 



131 

 315 

 420 

 443 

 728 

 833 



374 

 194 



Sulphuric Hydrochloric 



acid 



7-2 

 10-4 

 26-0 

 19-0' 

 27-5 

 24-2 



18-0 

 17-5 



acid 



91 

 17-3 



4-4 

 19-4 

 21-7 



It will be seen that the central localities show the largest deposits 

 of soot and acid; the sulphuric acid there forming from 6 to 9 per cent, 

 and the hydrochloric acid from 5 to 7 per cent, of the total deposit. 



But these impurities due to smoke pollution get not only on the leaf 

 but in it. It has already been seen that the stomata of leaves may be 

 choked by a tarry deposit. The leaf may also absorb sulphur dioxide 

 from the atmosphere partly through its stomata and partly in the case 

 of some leaves possessing a thin cuticle directly through the epidermis. 

 Hence the sulphur content of leaves will give perhaps one of the best 

 indications of the amount of smoke pollution. 



A very large number of leaves from different districts have been 

 analysed in this way, the figures quoted are those connected with the 

 laurel leaves referred to on p. 394, which were collected on February 15th, 

 1913. 



Annual deposit of 

 soot in tons 

 District per sq. mile 



Sutton Free from smoke pollution 0-31 



Weetwood Lane 42 0-66 



University 114 1-28 



Hunslet 539 1-98 



If this method is used for a comparison of the relative freedom from 

 pollution of different districts, two or three points must be borne in 



Percentage of S0 3 



in dry matter 



of leaf 



