Malta was one of 11 EU member states that reported having exceeded PM10 (particulate matter) limit values due to natural source contributions, according to a report entitled “Particulate matter from natural sources and related reporting under the EU Air Quality Directive in 2008 and 2009”, published by the European Environment Agency (EEA).

The report notes that while much of the air pollution that damages human health and the environment today is the result of human activities, natural sources also emit air pollutants that contribute to the exposure of European citizens and ecosystems to bad air quality – and potentially undermining EU member state efforts to meet the air quality standards set out in EU legislation.

Recognising the challenge presented by natural air pollution, the Air Quality Directive provides that, before member states compare ambient air pollutant concentrations with relevant legally binding limit values, they may subtract the contribution of natural sources.

Particulate matter consists of very small, suspended solid or liquid particles, which have short- and long-term effects on health, from general ill-health to respiratory problems such as asthma, as well as cardiovascular effects. Particulate matter originates mainly from fuel combustion in transport and power generation, quarrying and construction dust, mechanically-generated dust, tyre and brake abrasion, and aerosols of transboundary origin, but it also includes dust from natural sources.

The Malta Environment and Planning Authority’s (Mepa) recently published “The Environment Report: Indicators 2010-2011” states that in 2010, Malta’s real-time monitoring stations recorded high levels of PM10, although they are party from natural sources (such as atmospheric sea salt and wind-blown dust from the Sahara for instance), which may be deducted when computing final EU reporting figures, and thus compliance with EU standards.

The report says that Malta experienced higher levels of particulate matter in 2010, and EU standards were exceeded in Msida, which is the location most dominated by traffic.

The EU daily limit value of 50µg/m3 should not be exceeded more than 35 times a year (approximately 10 per cent of days measured). In 2010, the limit value at the Msida monitoring station was exceeded on 80 out of 340 days measured (23 per cent of days measured). Following deduction of natural sources, Msida was left with 37 exceedances (or 11 per cent of days measured).

In 2009, Msida had registered exceedances on 57 days, or 18 per cent of days measured, but 35 days when natural sources were deducted.

The threshold at the Għarb monitoring station was exceeded on 39 out of 326 days (12 per cent of days measured) in 2010, and the highest concentration for 2010, of 366µg/m3, was recorded in this locality.

Following deductions of natural sources, it emerged that all but one of the exceedances at this station were due to natural sources. In 2009 Għarb had registered 15 exceedances.

The EEA report states that 11 member states reported exceedances of PM10 limit values in 2008 and/or 2009 (Austria, Cyprus, Germany, Greece, France, Italy, Latvia, Malta, Portugal, Spain and the United Kingdom).

The daily PM10 limit value was exceeded more frequently and at more stations than the annual mean. The highest numbers of exceedances were reported by Mediterranean member states (Cyprus, France, Greece, Italy and Spain).

The highest number of stations reporting natural contributions was located in Spain, and the main natural source contributing to exceedances was “transport of natural particles from dry regions outside the member state” (Saharan dust), followed by sea spray and wild land fires.

Ten member states (Austria, Cyprus, France, Germany, Greece, Italy, Malta, Portugal, Spain and the United Kingdom) reported exceedances of the PM10 daily limit value due to natural contributions in 2008, and eight in 2009 (Cyprus, France, Greece, Italy, Latvia, Portugal, Spain and the United Kingdom).

The report describes wind-blown desert dust particles (African dust) as the transport of natural particles from dry regions, that is re-suspended and transported (wind-blown) desert dust particles that have a strong impact on atmospheric visibility and aerosol composition and on particulate matter levels. Arid zones in North Africa are the major source.

“For the western Mediterranean, Rodríguez et al (2001) and Escudero et al (2005) defined three scenarios typically favouring the transportation of mineral particles from the Sahara and Sahel deserts. The transport may be due to:

• A low atmospheric pressure system over the Atlantic (near Portugal) and/or over the Morocco area, normally in early autumn and spring.

• A high pressure system (at surface level) over the Iberian peninsula and western Mediterranean and/or over northern Africa. Such situations are generally observed in January–March, causing dust plumes to develop over the Atlantic with a well-defined convex morphology. The plumes can be transported towards the Iberian peninsula from the west.

• A North African anticyclone − a wind flow in the upper levels of the atmosphere associated with a high atmospheric pressure system. This is the most common scenario transporting African dust towards western Europe, mainly occurring in summer.

“For the central and eastern Mediterranean, Nickovic et al (2001), Kallos et al (2006 and 2007) and Meloni et al (2008) identified the two main meteorological situations responsible for the transport of large amounts of mineral dust particles:

In spring and early summer, Saharan thermal lows can develop in the south of the Atlas Mountains under the influence of the strong thermal contrast between the temperature of the cold marine waters and the warm continental surfaces (Moulin et al, 1998). Cyclones travel eastward along this thermal gradient and finally cross the Mediterranean between Libya and Egypt. They constitute the main atmospheric scenario responsible for the transport of desert dust over the eastern Mediterranean Basin.

Severe episodes can also be associated with the combination of a deep trough over the west Mediterranean and north-west Africa and relatively high pressures towards the eastern part of the Mediterranean. This scenario is related to the evolution scenario 1 in the western Mediterranean.