Bad news for air quality over World Trade Center

A group of Californian scientists have revealed that the level of fine particles near to the World Trade Center last October were higher than those found down-wind of the burning Kuwaiti oil fields in 1991, following the Gulf War. However, current air quality in the area is now no longer affected by the disaster.

Scientists from the University of California Davis’ DELTA Group (Detection and Evaluation of Long-range Transport of Aerosols) have analysed air samples taken from the beginning of October to mid-December from a rooftop one mile north-northeast of the Trade Centre complex. Their new report, concerning the samples collected throughout October, reveals that the levels of particles following the disaster were unprecedented, contradicting information given out by the Environmental Protection Agency (EPA).

“No one has ever reported a situation like the one we see in the World Trade Centre samples,” said University of California professor emeritus and head of UC Davis’ DELTA Group, Tomas Cahill. The group has made detailed studies of aerosols from the 1991 Gulf War oil fires, volcanic eruptions, global dust storms, and recently in Asia. “The air from Ground Zero was laden with extremely high amounts of very small particles, probably associated with high temperatures in the underground debris pile,” said Cahill. “Normally, in New York City and in most of the world, situations like this just don’t exist.”

Currently, there are no established safe limits for very fine particles, those 0.24 micrometers and below, though this reflects the fact that they make up only a small fraction of the total air mass. However, in the World Trade Center air samples analysed by the DELTA scientists, the very fine particles are a were large fraction of the total mass.

The amount of very fine particles at the sample site varied depending on the weather and wind direction, and decreased sharply throughout the month. On one occasion, the analysis revealed that there were 58 micrograms per cubic metre of very fine particles in one 45 minute period – “an extremely high peak”, said Cahill. He notes, however, that the levels of very fine particles at Ground Zero and some other parts of Lower Manhattan would have been even greater than those at the sample site.

The very fine particles contained high levels of sulphur and sulphur-based compounds, which appear in early samples to have been dominated by sulphuric acid. These particles also contained high levels of silicon, potentially from the thousands of tonnes of glass in the debris, say the group. “Even in the worst air days in Beijing, downwind from coal-fired power plants, or in the Kuwaiti oil fires, we did not see these levels of very fine particulates,” said Cahill.

Coarse particles, 5-12 micrometers in diameter, were found in similarly high concentrations. “These particles simply should not be there,” said Cahill. “It had rained, sometimes heavily, on six days in the prior three weeks. That rain should have settled these coarse particles.” These findings suggest that the particles were being continually generated from the hot debris pile, a theory supported by the fact that they appeared to be coated with combustion products, including soot.

Of the different metals – many widely used in building construction, wiring and plumbing, and some in computers – within the very fine particle size range, some were found at the highest levels ever recorded in air in the US, say the researchers. These include iron; titanium, which is associated with powdered concrete; vanadium, and nickel, which is often associated with fuel-oil combustion, which were found in relatively high concentrations in the very fine particle range. Mercury and lead were also seen occasionally in fine particles, but at low concentrations.

On the brighter side, only a very few fibres of asbestos were found, and although some glass particles were found, they were not in the form of the long shards which can mimic asbestos fibres.

The DELTA Group has also given a number of recommendations for safe cleaning of homes in the vicinity of the World Trade Center complex. Very fine particles will have penetrated crevices and fabrics in a way that normal dust does not, and are easily re-suspended in the air. Cahill strongly supports recommendations already made by the New York Department of Health regarding washing with water, and says that residents should:

  • not use vacuum cleaners or brooms because the re-suspend particulates, but instead use wet cloths and mops, and wet vacuum-type cleaners;
  • wipe all surfaces, including window blinds, picture tops and door frames, with web rags;
  • wash or dry-clean all curtains, steam-clean furniture fabrics, and wet-clean carpets;
  • use high efficiency electrostatic or HEPA air filters in furnaces and air conditioners; and
  • keep humidity reasonably high indoors, to prevent fine particles from floating around.

Environmental Protection Agency Administrator Christie Whitman has drawn criticism for announcing, shortly following the attack that the air was safe to breath (see related story), although, at the beginning of November the New York Daily News published a leaked EPA memo that revealed that the situation was more serious (see related story). Nevertheless, the Agency’s website still states that: “EPA’s air monitoring near the WTC has not detected any pollutants from the fire and building collapses that are of concern to the general public. Within the restricted zone – within one block of the WTC, EPA is finding low levels of asbestos in the dust from the building collapse.”

Three days after the publication of the research, the EPA declined to comment to edie, stating that the Agency had not yet seen the DELTA Group’s data.

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