7/16-17/99 Northeast Fine Particle and Ozone "Haze" Episode
The period of Friday, July 16th and Saturday July 17th, 1999 was characterized by extremely hazy conditions in The Northeast, associated with high concentrations of fine particles and ozone. The haziness off the north Atlantic coast is clearly evident in 7/16/99 SEAWIFS and GOES8 (visible) satellite images and in CAMNET photographs of the Boston Skyline. Preliminary ambient measurement data indicate that exceedances of the proposed 8-hour ozone standard (85 ppb) were recorded at 138 different sites in the Northeast Ozone Transport Region on 7/16, and at 100 sites on 7/17 - making this the worst 1999 regional ozone episode (so far) in the Northeast. EPA Ozone map animations for 7/16/99 indicate moderately high to unhealthy levels of ozone throughout the Northeastern US. High levels of 1-hour and 8-hour ozone were also reported in southern Quebec Province.
Only limited and preliminary measurements of fine particle concentrations are currently available, but these suggest 24-hour PM-2.5 levels ranging from 35 to 50 micrograms per cubic meter in the region during this 2-day period, including 7/17/99 concentrations of 50 ug/m3 in Bennington VT, 52 ug/m3 in Portland, ME and 51 ug/m3 in Roxbury, MA. Hourly (TEOM) measurements in Roxbury indicate peak 1-hour concentrations of 57 ug/m3 on 7/16, 64 ug/m3 on 7/18 and 88 ug/m3 on 7/17 - with average 24-hour concentrations of about 40 to 50 ug/m3 through this 3-day period. While PM-2.5 concentrations of 40 to 50 ug/m3 are well below the proposed 24-hour fine particle standard (65 ug/m3), they are as high or higher than than the worst historical PM-2.5 episodes in this region in recent years. Similarly high PM-2.5 levels were also observed in southern Canada.
Preliminary Nephelometer (and humidity) data from IMPROVE sites in Acadia NP, ME and Gt. Gulf, NH indicate some of the highest "filtered" light scattering (Bscat) levels ever recorded at these sites (250-300 Mm-1) despite atypically low nighttime humidity levels on the 16th and 17th. The unfiltered nephelometer data from Gt. Gulf show short-term extinction of nearly 1000 Mm-1 on the evening of 7/17. These levels are similar in magnitude to the peak extinction estimates derived from Burlington, VT Airport (ASOS) visibility observations during this time period, and also show a similar temporal pattern to the fine particle measurements in Roxbury, MA. All of the above continuous data show a surprisingly high degree of short-term temporal variation ("blobiness"), which provides an interesting contrast to the spatial uniformity of the daily average concentrations.
Backward air trajectories (NOAA HY-SPLIT) on 7/17/99 for Bennington, VT (which also recorded its highest 1999 8-hour ozone concentration of 93 ppb on the preceding day) suggest a classic case of pollution transport from the industrial Midwest. Backward trajectories from a location near Martha's Vinyard for the late evening of 6/16/99 suggest a more complex combination of transport flows - up the northeast urban corridor near the surface and from the midwest at higher altitudes - which is typical of some of the worst historical ozone episodes in costal New England. A similar transport pattern is indicated by calculations of the Canadian HTM trajectory model.
The high concentrations, multi-day nature and large regional extent of the episode have been well- characterized by the US Navy Aerosol Analysis and Prediction System (NAAPS), run continuously at the Naval Research Laboratory (NRL) in Monterey, CA (see Doug Westphal's Episode Summary for details). As the episode moves off the coast on July 18th and 19th, the NAAPS model (with good agreement from aerosol optical thickness estimates from the NOAA-14 AVHRR satellite) shows an unusually distinct "sulfate" plume stretching far out into the North Atlantic (at the same time a distinct plume of "Sahara dust" is approaching North America from the East).
Noted marine aerosol scientist Joseph Prospero of the University of Miami has suggested in an interview reported in the 7/28/99 Miami Herald that he believed "high concentrations of visibility-reducing aerosols were the cause of the crash that killed (John) Kennedy (Jr.) and his passengers" on the evening of 7/16/99. Washington University researcher Rudolph Husar has initiated a detailed assessment of Haze Conditions Near Cape Cod on July 16,1999 - based on satellite and surface meteorological and (ASOS) visibility observations. A report by John Blosser and Reginald Fitz in the 10/19/99 National Inquirer suggests that over-estimates of actual visibility conditions by the recently installed airport ASOS visibility sensors may have also been a contributing factor. While the causes or causes of this tragic accident may never be known with certainty, this was certainly a period of extremely high aerosol (and ozone) concentrations and poor visibility. It will be a useful episode for further analysis and modeling.
This summary, is intended to initiate the process of compiling relevant data and images to support further exploration. Groups or individuals with data to share or an interest in collaborative analysis of this episode are encouraged to contact Rich Poirot, VT Dept. of Environmental Conservation or Mario Benjamin, Environnement Canada - Région du Québec.
Figures and Tables for 7/16-17/99 Northeast Fine Particle and Ozone "Haze" Episode
states of: VA, DC, MD, DE, PA, NJ, NY, CT, RI, MA, NH, VT, ME
states of: VA, DC, MD, DE, PA, NJ, NY, CT, RI, MA, NH, VT, ME
