Air quality

Abstract

Since the writing of the first State of Environment Report in 1998, significant progress has been made in the generation of detailed knowledge regarding urban air quality in Malta. This was mainly due to the fact that, in 1999, the Environment Protection Department (EPD) initiated a National Air Monitoring Programme with the aims of providing an assessment of air quality based on scientific criteria and enabling urban air pollution mapping in the Maltese Islands.

The monitoring programme addressed both the determination of the spatial distribution of air pollutants as well as their temporal variation (i.e. to establish how pollutant levels or concentrations changed with time in any given place). For spatial distribution mapping, diffusion tubes are used that are exposed for a period in selected areas in Malta and Gozo.

Thirty-one sites, including four in Gozo were selected for such monitoring as shown in Table 9.1 and Figure 9.1. Four streets in each locality were chosen and the average value of the pollutant concentrations in each of these was taken as representative of the area. The air pollutants measured by this technique were sulphur dioxide, nitrogen dioxide, ozone and the hydrocarbons benzene, toluene, ethylbenzene and xylenes (BTEX). The diffusion tube samplers are exposed at the sites for a measured period and are then collected and sent to an analytical laboratory for chemical work up. This technique provides average concentrations over the measurement period. For temporal variation measurements, a mobile air pollution station was used equipped with apparatus that allows measurement of the following pollutants: sulphur dioxide, nitrogen monoxide and nitrogen dioxide (collectively referred to as NOx), ozone, carbon monoxide and also airborne particulate matter with aerodynamic diameter less than 10 micrometres (PM10). The mobile station is placed in a particular street for a period of one week where it collects readings of the five pollutants continuously for the duration of the period. The station is then moved to another street and more data is similarly collected. The mobile station was used to measure pollutants in similar localities to those involved in the diffusion tube measurements.