Air Quality Objectives / Targets NON - TECHNICAL GUIDE TO COLUMN HEADINGS ABOVE: - Pollutant The pollutant being measured, for example: SO2 is sulphur dioxide Concentration - ppb Refers to the upper 'acceptable' concentration for that pollutant (in parts per billion). Concentration - µg m-3 Refers to the upper 'acceptable' concentration for that pollutant (in micrograms per cubic meter). Measured as This is the duration type, for example 24-hour mean is the average reading for a full day. Date to be achieved by This column refers to the target date set by the Government to achieve this 'acceptable' level. For example, for Nitrogen Dioxide each District will have to try and have a level of 21ppb OR LESS by the end of 2005. The lower the level the better !