Fugitive mercury emissions from a chlor-alkali factory: sources and fluxes to the atmosphere

During winter 2000, a multi-organization research team assessed fugitive (non-stack) mercury air emissions at a chlor-alkali factory in the US using a variety of sophisticated mercury vapor analyzers to assess fugitive air emissions of mercury. The team obtained mercury data over a 9-day period from inside the factory, with the first known concurrent awareness of manufacturing operations. Emissions were measured from the roof vent, the open-sided basement below the production cells, and from surrounding soils and sealed waste ponds. Some emphasis was also placed on assessing the spatial distribution of Hg concentrations within an operating cell room. The team used real-time and near-real-time Hg analyzers including a Tekran 5-min integrated sampler modified for cell-room use, Lumex RA915+ and Jerome 431-X portable Hg analyzers, and a long-path integrating DOAS system for gaseous elemental Hg, coupled with an optical anemometer for measuring vent-averaged air flow rates. The integrated beam (DOAS) and point measurements of Hg° compared favorably. One principal finding is that fugitive air emissions from the cell-room roof vent are episodic and vary with factory operating conditions (maintenance and minor operational perturbations). Therefore, air emissions are likely to vary widely among factories on a worldwide basis, in accordance with operating procedures followed at each. Properly positioned, real-time mercury vapor analyzers are potentially valuable tools to locate small-scale process leaks, and to estimate overall emissions from the cell-room building. A preliminary estimate of daily fugitive Hg emissions during this period ( 400–600 g d−1) indicated that the bulk of the atmospheric loss was emitted from the roof vent of the main production building. Sealed waste ponds were not important sources, emitting Hg at rates comparable to background soils.