• concentrations
  • NO was once found in very low concentrations in the air until industrialization and human activities such as driving trucks, trains and cars changed atmospheric chemistry, Bryan says. (umass.edu)
  • pollution
  • Several years have passed since I first began to document the death of trees from air pollution, and it often feels there is nothing left to add as the trend accelerates - and is ever more assiduously ignored or misattributed. (blogspot.fr)