NEWS RELEASE February 2020
Should we be changing our definitions of air pollutants?
The definitions of air pollutant quantities are based on tradition and are often not the most accurate selections. Sensor based ambient air monitors are less costly than analysers or permanent samplers but there has been questions about their accuracy. Dubai solved this problem with a mobile EPA qualified analyzer system and fourteen Aeroqual sensor based systems. China has installed 10,000 Sailhero sensor based systems that correlate closely with analyzers for each of the major pollutants. The regulations relative to toxic metals require polluters only to limit PM 2.5 which is used as surrogate for toxic metals. This is despite the fact that some metals are 100,000 x more toxic than others. This is despite the fact that the employment of multi metals analyzers in a St. Louis ambient monitoring program showed that levels of certain highly toxic metals varied depending on the wind direction.
Opacity is still used for regulatory purposes. Its origin was long before scrubbers were employed after the particulate collector. In most cases scrubbers provide additional particulate removal but, in some cases, when they malfunction, they increase particulate discharges. But believe it or not opacity regulations require measurement prior to the scrubber since opacity cannot be measured in a wet stack.
Power plants and other combustion sources are required to limit their emissions of gas phase mercury. This is based on the fact that prior to attempted control mercury is in the gas phase. However, when activated carbon is injected, the mercury becomes attached to particles. If these particles are not captured, they can fall in the vicinity of the plant. In contrast gas phase mercury may travel across continents. It is therefore possible that mercury control could result in greater mercury contamination near the source than if there were no controls. Permanent samplers will capture particulate mercury but can be modified to segment the particulate and gas phase. The Cooper mercury analyzer also measures total mercury. Doesn’t it make sense to regulate total mercury?
The fundamental principles are also murky. Particulate is defined as the diameter of a sphere and the particle weight is assumed. In fact particles are not spheres and their specific gravity varies. The cascade impactor is used to determine particle size. But it creates its own definition which does not magically transform hair shaped particles into spheres of equal gravity.
The McIlvaine Company identified this problem relative to the sizing of wet high energy particulate scrubbers based on particle size. Purchasers who relied on particle size analyses in many cases experienced disastrous results. McIlvaine addressed this problem with the invention of the McIlvaine mini scrubber. It is a 1 cfm device where the energy in the turbulent zone can be varied and the results determined in mg/m3.
The impact of ambient particulate could be addressed in a similar manner. A miniature lung equivalent could be used to determine how much penetrates and how much is captured on the surface. It is likely that cascade impactor measured particles of 2.5 micron diameter penetrate differently. So the new definition would be particles which penetrate the lungs vs those which do not.
EPA standards for ambient measurement of pollutants have been adopted around the world. But when China and Dubai use methods which may be equally indicative even if they don’t correlate 100% with EPA methods, there is eventually going to be a movement toward a new standard.
Toxic metals need to also be addressed. The concern is not only the particle penetration aspect but the toxicity. There are now multi metals analyzers which can measure the concentration of 17 different metals. So the lung penetration index could also be adjusted based on a toxic metal harm quotient. In St. Louis when winds blow from the south, consistent with the bearing of the Doe Run Herculaneum lead smelter the toxic metal harm index is likely to be much higher than would be reflected by PM 2.5 measurement. McIlvaine has long promoted the use of a toxic metal harm metric which would take into account the relative contribution of each metal. This would be of more benefit to St Louis citizens. This common metric can be expanded to all pollutants and be a much better guide as to whether to remain indoors. This is explained at Sustainability Universal Rating System