Very Fine Aerosols from the World Trade Center ... - ACS Publications

Chapter 9

Downloaded by UNIV OF MASSACHUSETTS AMHERST on May 24, 2018 | https://pubs.acs.org Publication Date: November 15, 2005 | doi: 10.1021/bk-2006-0919.ch009

Very Fine Aerosols from the World Trade Center Collapse Piles: Anaerobic Incineration? 1

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Thomas A. Cahill , Steven S. Cliff , James F. Shackelford, Michael L. Meier , Michael R. Dunlap , Kevin D. Perry , Graham S. Bench , and Robert Z. Leifer 1

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DELTA Group, Department of Applied Science, University of California at Davis, One Shields Avenue, Davis, CA 95616 Department of Meteorology, University of Utah, Salt Lake City, UT 84112-0110 Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550-9234 U.S. Department of Homeland Security, Environmental Measurements Laboratory, 201 Varick Street, New York, NY 10014-7447 2

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By September 14, three days after the initial World Trade Center collapse, efforts at fire suppression and heavy rainfall had extinguished the immediate surface fires. From then until roughly mid-December, the collapse piles continuously emitted an acrid smoke and fume in the smoldering phase of the event. A knowledge of the sources, nature, and concentration of these aerosols is important for evaluation and alleviation of the health effects on workers and nearby residents. Here we build on our earlier work to ascribe these aerosols to similar processes that occur in urban incinerators. The simultaneous presence of finely powdered (circa 5µm) and highly basic (pH 11 to 12) cement dust and high levels of very fine (< 0.25 µm) sulfuric acid fumes helps explain the observed health impacts, as do the high levels of very fine 152

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

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mass and its constituents. The unprecedented levels of several metals in the very fine mode aerosols can be tied to the liberation of those metals that are both present in elevated concentrations in the debris and have depressed volatility temperatures caused by the presence of organic materials and chlorine under anaerobic conditions. Health concerns focus on the workers at the site, as plume lofting protected most of New York City.

Introduction The collapse of the World Trade Center structures (South Tower, North Tower, and WTC 7) presented two very different types of air pollution events as outlined in Chapter 2. These include the initial fires and collapse-derived "dust storm" and the continuing emissions from the debris piles. By September 14, three days after the initial World Trade Center collapse, efforts at fire, suppression and heavy rainfall had extinguished the immediate surface fires. From then until roughly mid-December, the collapse piles continuously emitted an acrid smoke and fume in the smoldering phase of the event. The presence of fuels, including diesel and electrical insulating oils and combustible materials in the WTC buildings, and lack of oxygen, were two factors that allowed the smoldering fires to bum for over three months. While this chapter focuses on the second air pollution event, the three month smolder phase, both situations shared the unusual aspect of a massive ground level source of particulate matter in a highly populated area with potential health impacts. The U.S. EPA has summarized five causal factors most likely to explain the statistically solid data connectingfinePM-2.5 aerosols and human health (1, 2). 1. Biological aerosols (bacteria, molds, viruses, etc.). 2. Acidic aerosols. 3. Veryfine/ultrafine( < 0.25µm)insoluble aerosols. 4. Fine transition metals. 5. High temperature organics. A knowledge of the sources, nature, and concentration of the WTC aerosols is important for the evaluation and alleviation of the health effects on workers and nearby residents. We especially needed to ascertain if these potentially causal factors of aerosol health impacts were present in the WTC plumes.


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Experimental Methods In order to better understand the WTC aerosols a slotted Davis Rotatingdrum Universal-size-cut Monitoring (DRUM) impactor, developed by the Detection and Evaluation of Long-Range Transport of Aerosols (DELTA) Group at the University of California at Davis (3-8) was shipped to New York and set up on the roof of the Department of Energy's (DOE) Environmental Measurement Laboratory (EML) at 201 Varick Street, 45 m above ground level and roughly 1.5 km north-northeast of the World Trade Center site. The DRUM operated until late December, after the last surface fires had been extinguished (9). The samples were collected in 8 size modes from the inlet (circa 12 pm) to 5.0 jum, 5-2.5 fim, 2.5-1.15 fim, 1.15-0.75 /zm, 0.75-0.56 jum, 0.56-0.34 jum, 0.34-0.26 fim, and 0.26-0.09 fim aerodynamic diameter. Samples were analyzed by a suite of non-destructive spatially resolved beam based techniques (7, 10, 11) for mass, hydrogen (as an organic surrogate), elements from sodium to molybdenum, some heavy elements by synchrotron x-rayfluorescence(S-XRF), and particle size by scanning electron microscopy. Time resolution ranged from 1 Vi hr to 3 hr depending on the size of the exciting beam. The presence of the WTC plume at the Varick Street site depended on both the source emission rate and the meteorology (12), with both wind direction and plume lofting from the hot collapse piles as the key parameters. In addition, the nature of the aerosols themselves, especially as they deviated in concentration, size, and composition from upwind and regional aerosols, also provided information identifying the WTC impacts at the site. We chose six parameters as tracers of the WTC plume. These parameters deviated by an order of magnitude or more from typical regional and urban values, and all of which appeared in time defined plumes of typically 3 to 6 hours duration. These parameters, listed in Table I, were used to establishing the influence of the WTC plume at the Varick Street sampling site. Five events observed at Varrick Street met all 6 criteria, four more events met 5 of the 6 criteria, and these 9 events are viewed as "highly probable events". Three events met only one or two of the parameters and these are assumed to be "non-WTC plumes" or uncertain sources, including a local power plant. Six of the events met 3 or 4 of the parameters and these are labeled "probable WTC influence". The analysis that follows uses only data from the 9 highly probable events. In terms of the WTC plume impact on New York City, on most days the plumes lofted above NYC, to roughly 500 m (13), so that only individuals on the collapse piles or very near the WTC site were subject to these aerosols.


155 Table I. Criteria for Establishing the WTC Plume Influence at the Varick Street Sampling Site.

Parameter type

Parameter definition


Very fine Aerosols Wind direction

0.26 - 0.09 pm HYSPLIT regional trajectories Organic matter by hydrogen (OMH) 5.0-2.5 pm 5.0 - 2.5 pm LaGuardia Airport visibility

Very fine organics Fine Cement dust Coarse Sulfate Ground based haze

Criterion for WTC influence 3

> 3 pg/m SSW quadrant > 1.0 pg/m

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Si: EF>2.5 > 0.3 pg/m L < 15 km 3

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# events meeting the criterion 18 14 +1 calm 16 16 15 5

NOTE: EF is enrichment factor. L is limit of visibility. v

Results Table II shows very fine particle concentrations for six of the highly probable events, plus background datafromOctober 7, a non-WTC plume event. We also include for comparison, datafromearlier studies of two highly impacted sites (2, 14, 15) with similar characteristics, namely a maximum 3 hr plume in a study of at least 4 weeks duration and using the same size and analytical protocols. Coarse particles at the sampling site were similar to the initial collapse aerosols (cement, dry wall, glass, etc.) (16), but also had chemicals and soot from the ongoing combustion (17, 18). The presence of unprecedented levels of very fine particles (0.26 - 0.09 pm) by mass and number in narrow plumes was more typical of an industrial source. Upwind sources were a very minor contribution as shown by direct comparison with upwind aerosol sites (9, 19, 20) and the size distributions were grossly different from typical ambient aerosols as described in Chapter 8 (21). Data taken within 200 m of the site by the EPA (19) and meteorological analysis (9) indicate the mean 24 hr PM-2.5 aerosol mass at the site was in excess of 200 pg/m from mid September through early October, much of it in the very fine and presumably ultra-fine modes, together with heavy PM-10 dusts. The veryfineparticle mass fell off sharply in October (9) and tests done near the 3


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Table II. Results of Very Fine Aerosol (0.26 - 0.09 pm) Sampling at Varick Street, October, 2001, Compared to Samples Obtained from Kuwait, July, 1991 (14) and Beijing during ACE - Asia, March, 2001(25). Date Oct. 7 Oct. 3 Oct. 4 Oct. 5 Oct.12 Oct.15 Oct.24 Oct.29 Kuwait Beijing

WTC impact No Yes Yes Yes Yes Yes Yes No

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Mass 0.5 50.6 9.3 4.7 8.2 4.8 3.8 2.4 Na Na

Organics 0.04 9.3 3.2 1.5 3.0 1.6 1.0 1.2 Na Na

Si0 0.02 1.4 2.6 0.9 2.9 1.3 0.2 2

0.07 0.6 1.1

H S0 0.1 17.1 3.7 1.9 2.2 1.1 1.6 0.9 5.5 6.7 2

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V 0.1 115 61 3 24 3 5 2 Na 0.8

Ni 0.1 22.7 8.0 1.3 7.1 17.3 6.7 1.6 5.0 1.8

NOTE: Units are //g/m .Units for V and Ni are ng/m . Na is not available.

WTC site for very fine particles in May, 2002, were generally < 10% of the October, 2001 24 hr average for plume impact days at Varick Street (22).

Discussion Plate 1 shows an example of typical crustal elements (silicon, calcium, iron, and aluminum) in the very fine (0.26 - 0.09 pm) mode from October 2 to October 30, 2001. There are several important points to note in this plate, First, the crustal elements aluminum, calcium, and iron seen so abundantly in the coarser particles are essentially absent in this veryfinemode. Thus, the signal is not due to a sampling artifact, as is also shown by the low silicon values in the sub-micron sizes, and the aerosol formation mechanisms are not simply mechanical grinding. Second, the silicon only appears when the wind is from the WTC site. Third, the peak values trend downward in October, and even the sample color grows fainter. October 24 was by all criteria (meteorology, coarse calcium, etc.) a very strong plume impact period, but by then the silicon has gone. The same pattern is seen in some other anthropogenic elements, notably vanadium, in both the coarse andfinemodes.



Plate 1. Typical crustal elements; silicon (—), calcium (—), iron ((—), and aluminum ( ) in the very fine particle mode (0.26 - 0.09 ixm) of samples obtained at Varick Strees during October, 2001. At top is shown the reflected light picture of this DRUM stage. Periods of favorable wind direction that would bring the WTCplume to Varick Street are indicated below the plot (—), Two rain events and an eastern ocean wind are also indicated.



158 These data then pose problems in determining the aerosol sources. We see aerosols typical of a high temperature industrial source, yet the temperatures in the near sub-surface collapse piles were not very high. We see some elements in the aerosols vastly enhanced over typical earth crustal values and others, equally present in the dust, absent in the aerosols. We propose a model derivedfromthe theory and data describing municipal incinerators. It was discovered that the presence of organic matter and especially chlorine in the wastes liberated metals during incineration by greatly reducing their volatility temperatures (23). In Table III, we present the concentrations in the WTC bulk dusts compared to their volatility temperatures in the presence of 10% chlorine for EPA criterion metals and a few other species of interest. These data are ordered by their volatility temperature (the point at which the vapor pressure reaches 10" atmospheres). The concentrations of many metals are greatly enhanced over typical Earth crustal levels, as to be expected in the smoking wreckage of highly computerized building. The top elements, chromium, beryllium, and barium, all have volatility temperatures that are probably higher than most parts 6

Table m. Concentration in the WTC Bulk Dust and Volatility Temperatures of Elements in the Presence of 10% Chlorine (23). Principal Volatility Dust Dust (16) Temp Species (24) Chromium 165 1594 C1O2/O3 71.5 Beryllium 1042 3.2 1.7 Be(OH>2 Barium 895 195 381 BaCl Nickel 43.5 686 15.5 NiCl Antimony SbjOj Na 653 Na Silver AgCl 2.3 620 4.9 Selenium Na

Very Fine Aerosols from the World Trade Center ... - ACS Publications

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