The article discusses gaseous air pollutants that have the greatest impact on forest ecosystems. This group of pollutants ncludes sulfur dioxide (SO2), nitric oxides (NO and NO2) and ozone (O3).
In the 20th century, the major contributor to forest degradation was sulfur dioxide, a gaseous substance with direct and powerful phytotoxic and acidifying effects. Since then, sulfur dioxide emissions have been significantly reduced in Europe and North America, but they continue to grow in East Asia along with China’s economic boom. Nitric oxides affect woody plants directly by entering through the stomata and indirectly through soil acidification and environmental eutrophication. Ozone, in turn, is found in photochemical smog and is produced by conversion of its precursors (nitric oxides, organic compounds and carbon monoxide). It is a strong oxidizing agent which disrupts various physiological processes, mostly photosynthesis and water use in plants, but is also the air pollutant that exerts the most toxic effect on forest ecosystems.