11th Conference on Atmospheric Radiation and the 11th Conference on Cloud Physics

Friday, 7 June 2002
Condensation nucleus, SO2 and NO2 concentrations in air arriving at Storm Peak Laboratory, Colorado during an east-wind event
Scott A. Dias, City College, New York, NY; and E. E. Hindman and T. J. Bandosz
Poster PDF (479.5 kB)

Meteorological data has been collected at Storm Peak Laboratory (SPL) in northwestern Colorado by CCNY students almost every January since 1990. During a period of clear air in January 2001, a distinct east wind was recorded. This east wind was unusual because the prevailing winter weather pattern at SPL is dominated by westerly winds. Using NOAA-HYSPLIT 72-hour back-trajectory analyses, three distinct source regions were identified. At the beginning of the event, the air originated from the SW, during the middle of the event it originated from the E and at the end of the event it originated from the NW. Further, air originating from the SW and E had similar condensation nucleus (CN) concentrations but the air from the SW contained significantly higher trace gas concentrations (SO2, NO2). The CN and trace-gas emissions for the two source regions (the Phoenix and Denver metropolitan areas) are expected to be similar. Thus, the similar CN concentrations and different trace-gas concentrations may have been due to inefficient scavenging of CN by cloud and precipitation formation but efficient scavenging of trace-gases. To test this hypothesis, radar images of precipitation were superimposed on the corresponding air-parcel trajectories. It was found that the parcels originating from the E experienced approximately 12 hours of precipitation while those from the SW experienced no precipitation. Thus, cloud and precipitation scavenging may have reduced the concentrations of trace-gas but not the concentrations of CN arriving at SPL from the E source region.

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