Dust dispersion in hard rock quarries

Open-pit quarrying constitutes a core industry in many countries. Significant dust emissions appear when different types of rock products, such as aggregates, are being produced. Dust causes harmful environmental effects. The aim of this study was to define the extent of dust dispersion and to find out critical parameters affecting it in hard rock quarries. The most critical parameters affecting the dust concentration and dispersion appears to be the wind direction, seasonal climatic conditions, number of crushing units and capacity of the drill. In addition, the commercial software AERMOD BREEZE for dust dispersion modelling was tested to find out the usability of short-term modelling results. Dust was measured in eight aggregate quarries and in two natural stone quarries. The measurements were made inside the quarry area with a nephelometer. Performed measurements and modelling results were compared with published data. During the production the dust concentration within aggregate quarries was a few thousand µg PM10/m3. The secondary crushing generated approximately 1 700 μg PM10/m3 and tertiary crushing about 3 400 μg PM10/m3, measured 50 m downwind from the source. Compared to crushing, drilling produced significantly less dust: between a few tens to few hundreds of µg PM10/m3. The background concentration of PM10 was reached at extrapolated distances of 750 m, 350 m, and 100 m from the tertiary crushing, secondary crushing, and drilling of natural stone, respectively. During the wintertime, the PM10 concentration near the secondary crushing was approximately 1 700 µg/m3, whereas during the summertime, it was roughly 170 µg/m3. Modelling performed well for crushing during the summertime as the modelled concentrations were same order of magnitude (93%) with the measured ones. However, modelling was unable to react sufficiently into ground inversion during wintertime and predicted concentrations of crushing were approximately 5% of the measured ones. The modelling was not able to predict reliably the hourly fluctuation of dust dispersion in the vicinity of a quarry. Modelling with on-site weather monitoring data and comparison of measured concentrations should be conducted to verify this conclusion.