Monitoring of air quality by planning authority

Mepa would like to clarify the following points emerging from the letter by George Debono entitled The Real Pollution Culprits (March 8).

When we refer to particulate matter (PM10), we are talking about particles with a diameter equal to or smaller than 10 micrometres generated from sources that are both man-made and natural as the transported dust from the Sahara and sea spray particles.

Calling natural sources an "old chestnut" undermines the significance and scientific facts attributed to the Sahara dust intrusion. There exist local studies which clearly indicate that natural contributions strongly contribute to PM10 ambient concentrations on the islands. One specific study concludes that most recorded PM10 concentrations registered by the Għarb air monitoring station are mostly associated with Sahara dust invasions.

In fact in 2008, this same monitoring station registered a total of 12 exceedances that were clearly attributable to this source. A Sahara dust event will not only affect Għarb but will affect the whole island. It is important to note that Mepa follows the methodology provided by the European Commission in the identification and quantification of Sahara dust events.

Secondly, it is an undeniable fact that given Malta's position, surrounded by sea, it is obvious that sea spray contributes to our PM10 levels, even more so during strong wind conditions. One can also reasonably assume that, once PM10 is formed from sea spray, it will disperse rather equally over the Maltese territory due to the large scale weather conditions. The contribution of sea salt to the PM10 concentration was estimated from measured chloride and sodium concentrations as guided by the European Commission.

This is something which all EU member states do, and was not the result of an ad hoc improvisation by Mepa, in order to try "painting a brighter picture of air quality in Malta", as was erroneously asserted by Dr Debono.

The fact that the exceedances of the daily standard for PM10 were brought down to 31 from 52 does not mean that ambient levels of particulate matter are no longer a concern or that the issue has been "swept underneath the carpet". Contrary to this statement, the Authority has worked on and published a rigorous air quality plan with the targeted aim of further lowering these exceedances.

Dr Debono also takes on Mepa for locating one of its air monitoring stations in the traffic hub of Msida, rather than in a "street canyon".

Dr Debono should note that the EU Air Quality Directive advises against the location of such traffic oriented monitoring stations in microenvironments like "street canyons" but in sites that can sample both the macro and micro environment. Msida meets all micro and macro-scale siting criteria.

As far as the inventory is concerned, Dr Debono has preferred to pass discrediting comments on Mepa's emissions inventory rather than update his information sources. According to the latest version of Mepa's inventory published last month, 88.7 per cent of the PM10 emitted by the transport sector in 2008 was due to heavy goods vehicles (HGVs) as opposed to only nine per cent of the PM10 emissions attributable to cars.

Mepa can also confirm that, according to this submission, from 2000 onwards HGVs have had the lion's share of PM emissions from the transport sector. Mepa considers the latest version to be the most accurate and updated version of the emissions inventory. Mepa also denies the assertion that its policies in the air quality field rely on the information from the inventory. This is not the function of the emissions inventories.

The public may wish to note that reports on this subject are available on the Mepa website www.mepa.org.mt/air-publications. Mepa remains totally committed to ensure that the quality of the air we breathe in Malta is clean both for our health and for our environment.