When a dust suppressant, such as Calcium Magnesium Acetate (CMA), is sprayed onto a surface it forms a hygroscopic coating, keeping the surface damp. When particulate matter comes into contact with a treated surface it is less likely to become resuspended, thus reducing the amount of particulate matter (PM) in the air. The CMA will only affect PM that comes into contact with the treated surface, therefore the greater the area treated the larger the potential benefits will be.
Studies in Scandinavia found that application of CMA-solution applied to the road surface of a highway reduced the daily PM10 levels by 35% on average. The use of CMA can therefore be an effective measure to reduce peaks of PM10 during very dry road conditions.
Trials of CMA dust suppressant on paved roads in London found that there was an observable level of improvement in 24 hour PM10 concentrations during low intensity application periods, with a potential reduction of about 10% at kerbside locations. Analysis of results from a more intense period of treatment suggest that there was a greater level of improvement, with approximately 14% reduction achieved. Calculations for the smaller size fractions of PM2.5 and PM1 suggest that improvements of around 3% were achieved during the intense treatment period. CMA interventions are anticipated to primarily affect larger sized particles so the lower improvements achieved would be expected for the smaller size fractions (Deakin 2011).
Subsequent trials carried out to evaluate the impacts of using CMA as a dust suppressant in London during 2011 indicated that there was limited impact when applied to the public highway. However, there was a far greater impact recorded in test areas close to industrial sites characterised by waste transfer stations and other processes generating unusually high levels of airborne dust. Benefits of CMA application were identified where the dust suppressant was applied to road adjacent to the sites and at the process yards themselves. One of the study areas, Horn Lane in Ealing, is adjacent to a mixed use industrial area comprising of a waste transfer station, aggregates handling, a cement batching plant and several other smaller operations. This site indicated a clear reduction in local PM10 concentrations in the hour following on-site CMA application of between 31% and 59% relative to the control.
For construction sites it was therefore recommended that CMA should be considered on haulage routes on and off site during the demolition and construction phases of large developments. Consequently, the GLA have recommended the dust suppressant for use at road sides and along roads close to and within construction and industrial waste sites with high levels of local PM pollution. In these cases, where CMA is applied to unpaved roads and haulage routes on construction sites there must be consideration made to dust being carried from the unpaved areas to the paved roads due to the strong dust binding effects of the CMA. To avoid trackout occurring onto the public highway constructions sites where CMA in being used should ideally also be equipped with wheel washing facilities.