The Castle Springs monitoring station in Moultonborough, NH. Photo: Kevan Carpenter

The diurnal (daily) cycle of carbon dioxide (CO₂) has been understood for some time; however, AIRMAP researchers have advanced our understanding of a diurnal pattern for ozone (O₃). In particular, they have provided an explanation for the low nighttime levels of ozone. The patterns are described in an article authored by CCRC scientists Robert Talbot, Huiting Mao, and Barkley Sive (see citation), and published in the Journal of Geophysical Research (JGR)

Ground level ozone is important to understand because it poses a serious health threat, particularly for those individuals who suffer from pulmonary conditions such as asthma. Ozone also plays a key role in understanding the complex manner in which pollutants and natural weather processes relate to one another in controlling chemical reactions in our atmosphere. AIRMAP maintains five measuring stations, distributed geographically throughout New Hampshire, and encompassing altitudes from sea level to the highest peak. This study drew on data from the two low-elevation, terrestrial sites—Thompson Farm in Durham (24 meters) and Castle Springs (406 meters) in Moultonborough.

The inner workings of the Thompson Farm monitoring site in Durham, NH. Photo: Kevan Carpenter

Ozone’s pattern is opposite that of carbon dioxide, with peaks occurring during the sunlit hours of the afternoon, and with nighttime levels frequently dropping to almost zero. The daytime creation of ozone results from a process called photolysis, in which sunlight initiates a series of chemical reactions with various other constituents in the atmosphere, forming ozone. In their study, Talbot and his colleagues explore the link between low nighttime ozone levels, and the cycles of nitric oxide (NO) and certain oxygenated chemical species, including methanol, acetaldehyde, and methyl ethyl ketone. The oxygenated species follow similar diurnal patterns to ozone indicating their removal from the atmosphere through dry deposition, whereas NO emitted from combustion sources such as automobile engines reacts with ozone to form nitrogen dioxide (NO₂): NO + O₃ --> NO₂ + O₂. In either case, the nighttime variability of these other species helps researchers to understand possible causes for the depletion of ozone. Research done by the AIRMAP program has helped describe the presence of these various pollutants, through an understanding of both sources and the mixing processes at play in our atmosphere.

You can look for the patterns described in this article by viewing the near real-time data collected at the AIRMAP measuring stations. This data can be accessed directly from this website’s homepage.

Citation

Talbot, R., H. Mao, and B. Sive (2005), Diurnal characteristics of surface-level O₃ and other important trace gases in New England, J. Geophys., Res., 110, D09307, doi:10.1029/2004JD005449. Abstract