Meteorology and Climate Influences on Tropospheric Ozone: a Review of Natural Sources, Chemistry, and Transport Patterns

Study key findings

• The study summarizes three dominant pathways of meteorological and climatic impacts on tropospheric ozone and presents their recent progress. 
• The three pathways are influences through changes in the natural precursor emissions, the kinetics and partitioning of chemistry and deposition, and the transport of ozone and its precursors.
  • (1) natural emission pathway: a large amount of ozone precursors are emitted from climate-sensitive natural sources such as lightning and biosphere;
  • (2) chemistry pathway: meteorological conditions such as solar radiation, temperature, and humidity alter the partitioning and efficiency of chemical reactions and dry deposition, and therefore modulate ozone production and loss; and
  • (3) transport pathway: as the lifetime of ozone and its precursors in the free troposphere can be longer than months, they are subject to changes of transport patterns on different spatiotemporal scales.
• Projections of future ozone changes driven by climate change largely reflect the dominant role of increasing temperature and water vapor in the atmosphere. These suggest increasing surface ozone in the polluted regions such as eastern US, southern Europe, and the south and east Asia, most likely due to increasing biogenic isoprene emissions, increasing solar radiation with less cloudiness, decreasing ozone dry deposition, increasing PAN decomposition, and higher frequency of stagnations and heat waves. 

Abstract

Tropospheric ozone is a key air pollutant and greenhouse gas. Its fate strongly depends on meteorological conditions and therefore subject to climate change influences. Such dependences through biogenic, chemical, and dynamic processes on different spatiotemporal scales have been unraveled from observations and modeling studies. In this process-oriented review, we summarize three dominant pathways of meteorological and climatic impacts on tropospheric ozone and present their recent progress. The three pathways are influences through changes in the natural precursor emissions, the kinetics and partitioning of chemistry and deposition, and the transport of ozone and its precursors. Tropospheric ozone levels have shown significant global or regional responses to meteorological/climatic changes (e.g., changes in the Brewer-Dobson Circulation, the Hadley Circulation, and El Niño–Southern Oscillation) and can be explained through the conjunction of these pathways. Most recent model projections predict that future climate will increase surface ozone in polluted regions and decrease ozone at a global scale due to stronger ozone chemical loss. However, uncertainties in climate-ozone responses and limitations in model capability still challenge the magnitude and even the sign of such projections. We highlight the rising importance of future increase of stratosphere-troposphere exchange in modulating tropospheric ozone that may largely compensate the predicted chemical loss of tropospheric ozone burden. We also highlight that uncertainties in isoprene chemistry, biogenic emissions in changing CO2 levels and vegetation, and interactions between ozone and vegetation may largely affect the surface ozone response to climate change. Future research and model improvements are required to fill these gaps.