Road transport major pollutant

Recent surveys by Eurobarometer show that the Maltese public is concerned about what air we breathe.

The mother challenge of them all in air quality is road transport

Air issues have typically focused on chimney stack emissions from the obsolete but as yet indispensable Marsa power station, taking stock of residents’ plight, and generations of them, with what they endure as a consequence of background and sporadic black dust manifestations from the plant.

In the thick of a general election campaign that shall be remembered for all the prominence that has been given to energy issues and the future of power generation in Malta, the Delimara power station has taken the resemblance of Dr Jekyll and Mr Hyde. The electorate has to discern between the plant as a potentially cancer-causing agent and the claims by some prominent politician that not one single particulate can be seen while the new BWSC engine is in operation.

Irrespective of how it goes beyond the Ides of March and whether we will have to wait a full eight years or more until we finally get connected to a natural gas pipeline supply for cleaner energy, the discussion on energy seems to be missing one important point. When all is said and done about power generation, Malta will still have to grasp the bull by its horns on air quality by tackling the mother challenge of them all: road transport.

Recent NSO statistics give the stock of licensed vehicles at the end of 2011 totalling at 311,947 as compared to 304,705 in 2010.

Petrol and diesel engines on our roads tallied at 193,003 and 118,538 respectively by end 2011, plus 28 battery-operated vehicles, 233 hybrids and 75 electric cars.

All of them on a road network of about 3,000 kilometres.

Vehicle average age at the end of 2011 stood at 13.86 years compared to 13.80 for 2010 and the number of vehicles per 1,000 residents had risen from 730 to 748.

Road transportation consumed 157,398 metric tonnes of fuel in 2010 compared to 153,520 in 2011 and 129,444 metric tonnes in 2000.

The build-up of particulates in ambient air from fossil fuel combustion sources is a grave matter from both an environmental and a human health perspective.

Chimney stacks releases from power stations send pollutants high up into the air and these will disperse safely onto the sea for as long as the prevailing meteorological conditions are in that direction. In several instances, however, this does not happen and the pollution shifts onto urban areas.

The consequences can become far more serious under stagnant air scenarios both in winter, on, say, very cold early mornings, or in summer during the hot July-August calm.

Soot-blowing episodes and insufficient chimney stack height further aggravate the situation. But this is only one side of the story.

Vehicular emissions include particulate matter mostly from the low-end of the aerodynamic diameter range. This ‘black dust’ is much less visible than Marsa emissions at their worst, more inhalable, given the topographical circumstances in which it forms, and, clearly, much less easily dispersed.

Our roads exhibit a so-called street canyon effect that invariably tends to trap vehicular emissions for longer times and closer to the ground.

Chemical composition of particulate matter is clearly dependent on the source. Limestone dusts from quarrying activity, also known as ‘white dusts’, are mostly calcium carbonate. The urgency to implement measures that tackle this kind of dust has been highlighted in various reports. Airborne calcareous dusts tend to neutralise any acidifying effects resulting from sulphurous or nitrogen oxide emissions from power stations.

‘Black dusts’ or soot from fixed or mobile combustion sources, on the other hand, is made up of a carbon core that acts like a sponge onto which other toxic substances adhere. These toxics include heavy metals – such as nickel and vanadium, characteristically released from heavy fuel oil combustion – and other substances known as polyaromatic hydrocarbons, PAHs, whose carcinogenic nature has long been known.

Soot formation from vehicular internal combustion engines is known to be favoured under fuel-rich conditions. A first step towards controlling particulate emissions from cars is thus adequate regular maintenance. Old engines with low performance coefficients are the worst emitters from both a particulate matter and volatile organic compound perspective. The latter basically consists of releases of unburnt fuel that actively participate in the chemistry of polluted air under the influence of sunlight. One result is ozone, a respiratory irritant whose formation is triggered by its nitrogen oxide precursors.

Local knowledge about the impacts of particulate emissions from vehicular sources remains very limited, sparse and fragmented. A thorough investigation into the chemistry of airborne particulate matter from vehicular sources is needed to assess whether PAH levels in ambient air may actually be one of Malta’s major health threats.

sapulis@gmail.com

Alan Pulis specialises in environmental management.