Urban Aerosols and Their Impacts - American Chemical Society

Chapter 15 2 1 0

Po/

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in Outdoor-Indoor PM-2.5, and PM-1.0 in Prague, Wintertime 2003 1

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Jan Hovorka , Robert F. Holub , Martin Braniš , and Bruce D. Honeyman 2

Downloaded by CORNELL UNIV on October 27, 2016 | http://pubs.acs.org Publication Date: November 15, 2005 | doi: 10.1021/bk-2006-0919.ch015

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Institute for Environmental Studies, Faculty of Science, Charles University in Prague, Benátská2,128 01 Prague 2, Czech Republic Environmental Science and Engineering Division, Colorado School of Mines, Coolbaugh Hall, Golden, CO 80401 2

After the large aerosol releases that occurred during the WTC collapse there was a significant amount of particulates that were transported inside the nearby buildings. This type of transport is occurring in many urban areas and is particularly significant for fine aerosols in the sub micron size ranges. The Pb net alpha activities and the mass concentrations of 24hour and 15-min averages of PM-2.5 outdoor/indoor and PM1.0 indoor aerosols were employed to determine penetration factors of outdoor PM-2.5 into a naturally ventilatedflaton the third floor in Prague center. The PM-2.5 penetration factors were in a range of 0.42 - 0.54. The factor values determined from alpha activities were higher than the factors derived from mass concentrations. The discrepancies can be explained by size selective aerosol penetration through the building envelope, which favors aerosol particles of smaller sizes having a higher specific alpha activity than larger ones. Both the alpha activities and the 24-hour mass concentrations of PM-2.5 did not reflect personal activities indoors unlike the 15-min mass concentrations. The 15-min averages also 210

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© 2006 American Chemical Society

Gaffney and Marley; Urban Aerosols and Their Impacts ACS Symposium Series; American Chemical Society: Washington, DC, 2005.

301 exhibited the highest temporal variation. Nevertheless, all three variables gave similar penetration factors. Both the alpha activities and 24-hour mass concentrations have shown indoor PM-1.0 to comprise about 70% of the indoor PM-2.5. The penetration factors and ratio of indoor PM-1.0 to indoor PM2.5 were constant during the sampling campaign. Indoor aerosol concentrations were affected predominantly by the outdoor aerosol concentration.


Introduction After the large aerosol releases that occurred during the World Trade Center collapse there was a significant amount of particulate matter (PM) that was transported inside the buildings in lower Manhattan. This type of transport is occurring in many urban areas and is particularly significant forfineaerosols that are in the submicron size ranges. The work presented here describes the use of natural radionuclides that are attached to these fine aerosols to determine the extent of this type of aerosol infiltration into buildings. The long-lived R n decay products Po and Pb present unique tracers for the study of atmospheric aerosol transport (1). These decay products can also be used as markers of outdoor aerosols penetrating into indoor environments (2, 3). This marker method is based on a well-justified assumption that there is no notable source of Pb indoors. The Pb net alpha activities and the mass concentrations of 24-hour and 15-min averages of fine (PM-2.5) outdoor/indoor and ultrafine (PM-1.0) indoor aerosols were employed to determine the penetration factors of outdoor PM-2.5 into a naturally ventilated flat on the third floor in the Prague city center. The indoor/outdoor penetration factors ( Cmass, Cmass, and Caipha) of atmospheric aerosols were determined from the slopes of the linear regressions of indoor against outdoor values of the 15-min, and 24hour mass concentrations and alpha activities, respectively (4). 222

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Experimental Methods The PM-2.5 indoor/outdoor and PM-1.0 indoor aerosols were sampled using a Harvard hnpactor at an airflow rate of 10.0 1/min and 23 1/min, respectively. Samples were collected for 24 hours on a single polytetrafluorethylene (PTFE) membrane. The volumetric (|xBq/m ) and specific (Bq/g) activities of Pb/ Po were measured by means of a a-spectrometer equipped with a multichannel analyzer (Canberra MCA) by using the Po alpha 5.3 MeV peak. Correction was made for additional alpha activity due to Pb decay and the net activity of Po was calculated. The ratio of Po/ Pb, based on repetitive measurements of aerosols sampled by the same technique in 2002, 3

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was estimated to be 0.2. The 15-min averages of PM-2.5 indoor/outdoor mass concentrations were determined by a laser photometer (TSI 8520 DustTrak) and values were corrected for changes in humidity and aerosol particle size distribution (5). Also, 24-hour concentrations of the gaseous atmospheric constituents nitrogen oxide (NO), nitrogen dioxide (N0 ), and ozone (0 ) were calculated from 15-min averages simultaneously measured indoors and outdoors (Horiba; APNA-360, APOA-360). Hourly averages of personal activities (e.g. number of people present, cooking activities, vacuum cleaning, ventilation, etc.) were recorded in a diary. The sampling campaign was conducted on daily basis from February 7 - March 13, 2003 in the living room of a three roomflaton the third floor of an apartment house situated in the Prague city center. A five-person family occupies this no-smoking flat. Downloaded by CORNELL UNIV on October 27, 2016 | http://pubs.acs.org Publication Date: November 15, 2005 | doi: 10.1021/bk-2006-0919.ch015

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Results and Discussion One of the main tasks in indoor/outdoor air quality studies is the estimation of how much outdoor aerosols penetrate indoors. Our results have shown that the Cmass is constant over a broad aerosol concentration range. According to the 24-hour averages of indoor PM-1.0 and PM-2.5 and outdoor PM-2.5 aerosol mass concentration shown in Figure 1,46% and 33% of outdoor P M 24h

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PM-2.5 outdoor (//g/m ) Figure 1. Average 24-hour mass concentrations ofPM-2.5 (Q) and PM-1.0 (A) indoors (IN) versus PM-2.5 outdoors (OUT).


303 2.5 contributes to indoor PM-2.5 and PM-1.0, respectively. Also, 71% of the indoor PM-2.5 mass is due to PM-1.0, as determined from the slope of the regression line shown in Figure 2. The Cmass values shown in Figure 3 are higher than ^Cmass of Figure 1. The higher temporal variations of 15-min mass concentrations, probably reflecting personal activity indoors, result in a lower correlation in Figure 3 (R = 0.64) than obtained in the case of 24-hour mass concentrations (R = 0.95). The volumetric Po net activity in PM-2.5, shown in Figure 4, is usually higher outdoors than indoors because of the higher outdoor mass concentration of PM-2.5. In contrast, the Po specific activity in PM-2.5 is higher indoors than outdoors. This mainly reflects the particle size-selective penetration through the building envelope that favors particles of the 200-500 nm sizes which carry more Po and Pb due to their larger surface area per unit mass than particles of the 500-2500 nm size range (2, 3). Also, the increase of indoor specific activity, but to a lesser extent compared with the penetration effect, l5m

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PM2.5 indoor Qigrr?) Figure 2. Average 24-hour mass concentrations of PM-1.0 indoors (IN) versus PM-2.5 indoors.


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Figure 3. Average 15-minute mass concentrations of PM-2.5 indoors(IN) versus PM-2.5 outdoors (OUT).

can also be caused by the lower values of indoor plate-out rates for the 200-500 nm sized particles. The Caipha (0.57, R = 0.73), obtained from Figure 4, is higher than the ^Cmass (0.46, R = 0.95), but very close to the C^ (0.54, R = 0.64) values (see Figures 1, and 3). Similar to the 15-minutes mass values, the regression line of the alpha activities does not have as tight a fit as do the 24-hour values due to the experimental error of the activity measurements which is on average 11%. The proportionality of indoor PM-1.0 to indoor PM-2.5, a value of 71% (R = 0.76) obtained from the alpha measurements shown in Figure 5, agrees well with the value of 72% (R = 0.96) estimated from the 24-hour mass concentrations (Figure 2). The building ventilation rate was calculated to be -0.36 ± 0.12 h" . This rate was determined on the basis of the disappearance rate of NO produced indoors. A non-ventilated gas stove in the kitchen is a strong source of NO indoors. Such a source significantly prevails over the outdoor NO sources and NO production indoors is clearly associated with the intensity of cooking. Typical time 2

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Figure 4. Volumetric Po net activity in PM-2.5 (O) and PM-1.0 (A) indoors (IN) versus PM-2.5 outdoors (OUT).

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Figure 5. Volumetric Po net activity in PM-1.0 indoors (IN) versus PM-2.5 indoors


306 evolution of NO concentration caused by cooking is depicted in Figure 6. Cooking activities initiated between six and seven o'clock cause a steep growth followed by an exponential decrease of NO concentration in the living room. Nevertheless, while NO produced in the kitchen is easily spread throughout the whole flat causing occasional peak values around 0.30 mg/m in the living room, our results of aerosol measurements clearly have shown that no significant mass of aerosol produced by cooking in the kitchen penetrates into the living room where the measurements were conducted. The reason for such a behavior is the high plate-out rates of cooking-associated particles with median diameters well below 100 nm (6, 7).


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Figure 6. Typical time evolution of NO concentration indoors recorded in the living room on March 4, 2003.

Conclusion 210

The measurement of Po alpha activity in low-volume aerosol samples allows for the determination of indoor and outdoor aerosols present in the indoor air and for a reliable estimation of penetration factors of outdoor aerosols into buildings. Such factors are key in assessing indoor/outdoor air quality relationships. Results of this study also have shown that losses of outdoor


307 aerosol particles during the infiltration through the building envelope were the most important process governing indoor aerosol concentrations.


Acknowledgment The sampling campaign went within theframeworkof cooperative research performed in several European urban areas funded by E U as the URBANAEROSOL project (Characterization of Urban Air Quality - Indoor/Outdoor Particulate Matter Chemical Characteristics And Source-to-ftihaled Dose Relationships) under grant EVK4-2000-00541. Careful sampling of all the PM's by M.Domasova and P.Rez&cova is gratefully acknowledged. Alpha counting was done in the LAER laboratory of the Colorado School of Mines and supported by grant of Charles University in Prague 206/2001 B GEO, PrF.

References 1.

Marley, N.A.; Gaffiiey, J.S.; Drayton, P.J.; Cunnigham, M.M.; Orlandini, K.J.; Paoda, R. Aerosol Sci.Technol. 2000,32, 569. 2. Mosley, R.B.; Greenwell, D.J.; Sparks, L.E.; Guo, Z.; Tucker, W.G.; Fortmann, R.; Whitfield, C. Aerosol Sci.Technol. 2001,34,127. 3. Harley, N.H.; Chittaporn, P.; Fisenne, I.M.; Perry, P. J.Environ. Radioactiv. 2000,51,27. 4. Nf Riain, C.M.; Mark, D.; Davies, M.; Harrison, R.M.; Byrne, M.A. Atmos. Environ. 2003,37,4121. 5. Ramachandran, G.; Adgate, J.L.; Pratt, G.C.; Sexton, K. Aerosol Sci.Technol. 2003,37, 33. 6. Long, C M . ; Suh, H.H.; Koutrakis, P. J.Air&Waste Manage Assoc. 2000,50, 1236. 7. L i , C.S.; Lin, W.H.; Jenq, F.T. Environ. Int. 1993,19,147.


Urban Aerosols and Their Impacts - American Chemical Society

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