A review of surface ozone background levels and trends

摘要: Abstract A survey of the literature was conducted to review historical and current surface ozone data from background stations in Canada, United States around world for purpose characterizing levels trends, present plausible explanations observed trends explore projections future levels. The annual cycle at sites Northern Hemisphere is characterized by a spring maximum, peaking during month May. Although presently there no concensus as origin evidence supports both enhanced photochemistry free troposphere stratospheric input. Modern day average concentrations over midlatitudes range between approximately 20–45 ppb, with variability being function geographic location, elevation extent anthropogenic influence. Annual median Canadian fall 23 34 ppb, similar that reported low-elevation world. Comparisons those measured century ago indicate have increased two times. are not uniform, some indication continued rise past three decades, this has been 0.5–2% per year. Rising were steeper 1970s 1980s compared 1990s, which seen either leveling off or decline magnitude these trends. Model sensitivity studies NO x emissions account greatest increase decades. substantial component concentration western North America may be due long-range transport Asian pollution, especially months. using IPCC emission scenarios 21st would exceed internationally accepted environmental criteria human health environment.