Urban Pollution

The discovery of the thinning of the Antarctic ozone layer every austral spring led to intense discussions at the international level and culminated in the historic agreement of September 1987: the Montreal Protocol on Substances that Deplete the Ozone Layer. Along with the subsequent London Amendment in 1990 and Copenhagen Amendment in 1992, the Protocol called for the elimination of production and consumption of CFC-11, CFC-12, CFC-113, CH3CCl3, CCl4, and halon-1211, among other targeted gases, in developed countries by 1 January 1996.
To test the efficacy of this international treaty, measurements of 14 ozone-depleting and/or greenhouse gases were taken above the forest canopy at Harvard Forest every 24 minutes, downwind of the New York City—Washington, D. C. corridor. Using a four-channel gas chromatographic system called FACTS (Forest and Atmosphere Chromatographs of Trace Species), observations of H2, CO, CH4, methyl chloroform (CH3CCl3), chloroform (CHCl3), carbon tetrachloride (CCl4), CFC-11 (CCl3F), CFC-12 (CCl2F2), CFC-113 (C2Cl3F3), halon-1211 (CBrClF2), perchlorethylene (C2Cl4), trichlorethylene (C2HCl3), nitrous oxide (N2O), and sulfur hexafluoride (SF6) began on 15 January 1996 and have continued with some interruptions to the present day.

Harvard Forest is ideally situated for a study of the pollution history of the Northeast urban/industrial corridor. As a trajectory analysis indicates, winds are predominantly from the west, with ‘clean’ background air from the northwest (Canada) and ‘dirty’ polluted air from the southwest (New York City—Washington, D. C. corridor). Because winds from the east are rare (~10% of the time), typically occur during stormy weather, and carry an ocean signal, such data are removed from the data analysis.
 
For two of the measured gases, CO and PCE (perchlorethylene, C2Cl4, used primarily in dry-cleaning and as a degreasing agent), inventories of ground based emissions are available on a county-wide basis for the Northeast. Using these two species as reference gases, we can determine the annual urban/industrial emissions of the other measured species. For those gases regulated by the Montreal Protocol, our results indicate that, after an initial decade of decline, the post-1996 emissions are not dropping as rapidly as expected or assumed.


References

This research has been funded by NASA, NOAA, DOE, and Harvard University and has resulted in 1 doctoral thesis, 4 papers, 2 conference presentations, and 1 prize.

For more information, contact Diana Barnes or Elaine Gottlieb.

For more information, contact Elaine Gottlieb.