Fine dust emissions from softstone quarrying in Malta

Abstract

The Lower Globigerina Limestone (softstone) provides stone blocks for the construction industry in Malta: primitive techniques are used to extract and convert limestone into such blocks. An analysis is presented of the work methods and practices employed by the industry, along with estimates of fine respirable dust (PM10) emission from such techniques, to show that the rate of PM10 emission is 0.38 kg of limestone dust per building stone produced; taking into account mitigation of dust release during the wet months, it is estimated that the 67 active open pit quarries which lie in close proximity (0.2 to 2 km) to urban centres generate, annually, about 1200 t of PM10 dust. Considering that dust emission occurs mainly during the dry summer months, the average PM10 emission rate from quarries during this period is 11 500 mg m-2 day-1 which is well above international guideline values (100 – 350 mg m-2 day-1). The main emission sources accounting for 97% of fine dust are the cutting tools (76%) used to extract the mineral from the quarry bed and the dressing tools (21%) that convert the blocks into ‘fair-faced’ stones suitable for use in construction. The reason why emission factors are so large is due to the fact that all dust generated is allowed to escape unchecked to atmosphere. It is concluded that in view of the magnitude of the emissions and the vicinity of sources to residential areas, the quarrying industry may be a significant factor contributing to the lowering of air quality on the islands with possible impacts on the health of the general population and, in a more serious manner, that of the quarrying community. Artificial water wetting of the quarry bed prior to extraction may provide an effective and relatively cheap mitigation measure during the dry weather when the problem of dust emission is at its worst.