NYC-WTC_000223635

NYC 9/11 Public Portal Document

Mr. Bernard P. Orlan July 3, 2002 Respirable Particulate Assessment Pages P.S. 15QM ATC Project No. 15-19125-0289

TABLE 2 COMPARISON OF 24-HOUR AVERAGE PM^g CONCENTRATIONS BY SAMPLING DEVICE (ug/m’)

LOCATION / DATE DUST-TRAK* MEM* (Pg/m’) (Itg/m’)

Main Lobby 4/1/2002 16 3.47

Main Lobby 4/8/2002 23 3.47

Main Lobby 4/15/2002 42 6.94

Main Lobby 4/22/2002 11 4.17

Main Lobby 4/29/2002 11 11.8

DISCUSSION

The concentrations on April 1-22 in the main lobby as measured by the Dust Trak® were higher than those measured with the MEM®. Levels as recorded by the Dust Trak® ranged from 2.6 to 6.6x’s higher than the gravimetric sample. The Dust Trak® detects volatile aerosol particles that are not recovered by the gravimetric method. However on April 29, 2002, the gravimetric sample results were only 0.8 pg/m’ higher than the Dust Trak®. The Dust Trak® data summaries and graphs arc provided in Attachment 1, the laboratory results of the MEM® samples are provided in Attachment 2.

These measurements confirm that the Dust Trak® reads different than the gravimetric sampler (MEM®) However, data collected to date do not indicate that there is a consistent factor that may be used to correlate the results of these two methods.

CONCLUSION

Sample results obtained on April 1, 8, 22 and 29, by both methods were below both the EPA NPAAQS for PMj 5 of 65 ug/m’ (24-hour average) and the EPA recommended level of 40 ug/m’. On April 15, the Dust Trak® result was slightly higher than the EPA recommended level of 40 ug/m\

CITY_21MC100_002919553

NYC-WTC_000223635