Flight Statistics, 1996-2003

Backtrajectory clusters
Backtrajectory clusters
with  NOx and SO2 emissions

Morning and afternoon
of all species

Morning and afternoon profiles of all species
for cluster analysis
Boundary layer column content
of all species for cluster analysis

Since 1997, hundreds of summertime flights designed to measure O3, CO, SO2, and aerosol optical and microphysical properties over the Mid-Atlantic have been conducted as part of the Regional Atmospheric Measurement, Modeling, and Prediction Program (RAMMPP).  To investigate diurnal patterns, median morning and afternoon profile values were calculated.  Little diurnal variation was identified in the CO, SO2, and Ångström exponent profiles.  Ozone values were larger in the afternoon due to photochemical production.  Lower free tropospheric O3, subject to long range transport, was invariant at ~55 ppb.  The single scattering albedo increased from morning to afternoon (0.94 vs. 0.93 in the boundary layer) due to SO2 oxidation.  In the morning and afternoon single scattering albedo profiles, the values decreased with altitude, likely due to the preferential rain out of SO42- dominated particles over black carbon particles.  An agglomerative, hierarchical cluster analysis of backtrajectory data in conjunction with the vertical profile data was used to identify the source regions and characteristic transport patterns during summertime pollution episodes.  Eight clusters were identified.  The clusters were divided into morning and afternoon profiles.  The northern Ohio River Valley was identified as the predominant source of power plant pollution, with large O3 values, highly scattering particles, and large aerosol optical depth.  Flow from the southern Ohio River Valley, in contrast, brought little pollution.  The greatest afternoon O3 values occurred during periods of stagnation when transport was minimal and photochemical production was encouraged.  North-northwesterly and northerly flow brought the least pollution overall. Ozone transport was quantified by calculating the ratio of residual layer O3 in upwind morning profiles to downwind, afternoon O3 profiles.  The greatest transported O3 came from the Ohio River Valley.  The least O3 was transported during periods of clean, northerly flow and when stagnation dominated.  The use of the clustering techniques with aircraft vertical profile data provided greater insight into the transport processes, dynamics, and underlying mechanisms that drive pollution events than when used with surface-based data.  The results will be useful in designing regional pollution control strategies, validating air quality models, and predicting future pollution episodes. 

Maryland Department of the Environment
University of Maryland