Climate Change and Your Health: Rising Temperatures, Worsening Ozone Pollution

I. Ground‐level Ozone Formation a. Precursor (Ozone‐Forming) Emissions Ground‐level ozone (O3) is produced by a complex set of atmospheric chemical reactions that depend on precursor (ozone‐forming) emissions from numerous sources, both natural and of human origin. Ground‐level ozone formation is also dependent on weather and climatic factors. Temperature is an important factor in both weather and climate and is a focal point in this report. The primary chemical species involved in ozone formation are nitrogen oxides (NOx), a combination of nitrogen monoxide (NO) and nitrogen dioxide (NO2); methane (CH4); volatile organic compounds (VOCs); and carbon monoxide (CO). Emissions of NOx due to human activities arise primarily from fossil fuel combustion, with vehicle exhaust, maritime shipping, and power plant energy production contributing the largest amounts (Cofala et al. 2007). Natural global emissions of NOx are uncertain, but may be of equal magnitude with emissions from human activities. Some of the important natural sources are lightning, emissions from soil bacteria, and forest fires (The Royal Society 2008). Natural VOC sources outweigh sources from human activities and are primarily emitted by terrestrial plants with isoprene being the dominant VOC species (Guenther et al. 2006). Human activity‐based VOC sources include fossil fuel combustion sources similar to NOx, as well as evaporation from solvents and coatings such as paint (Warneke et al. 2007). Methane emissions from human activities include landfills, agriculture activity, and raising livestock while natural sources include emissions from wetlands (NOAA 2010). Methane concentrations in the atmosphere have been roughly constant between 1999 and 2007 (NOAA 2010), but there is a slight indication of an increase through 2010 and there are many uncertainties in how the rate of release from natural sources, such as permafrost, may be affected by climate change (Archer 2007). Carbon monoxide sources include man‐made and natural combustion, and emissions from terrestrial vegetation and the oceans. Atmospheric CO concentrations are decreasing overall in the United States (EPA 2011a).