6.0 Particulate Matter (PM₁, PM₂.₅, PM₁₀)
Fine particulates like PM 2.5, PM 10 and PM 1, are harmful because they penetrate deep into lungs and even the bloodstream. In Ireland, PM 2.5 must not exceed an annual mean of 30 µg/m³, and PM 10 must stay under 50 µg/m³ for 24 hour averages—violations allowed only 35 times per year.
6.1 Nitrogen Dioxide (NO₂) & Nitric Oxide (NO)
Nitrogen oxides from traffic and combustion—especially NO 2 can inflame airways and aggravate asthma. Ireland’s limit is an annual mean of 40 µg/m³ and a 1 hour mean of 200 µg/m³ (with a maximum of 18 exceedances/year) . While there’s no specific standard for NO, its impact is included under NOₓ objectives
6.2 Ozone (O₃)
Ground-level ozone is a secondary pollutant created by sunlight acting on NOX and VOCs. Short-term spikes can irritate lungs and reduce lung function. Ireland follows EU target values (not legally binding) under the CAFE Directive; exceeding them can trigger action plans.
6.3 Sulphur Dioxide (SO₂)
SO 2, produced by burning fossil fuels, irritates the respiratory system. Irish standards require it to remain below 350 µg/m³ averaged over 1 hour (no more than 24 exceedances yearly) and below 125 µg/m³ over 24 hours (max 3 exceedances/year). Long-term, it must stay under 20 µg/m³ annually to protect vegetation.
6.4 Hydrogen Sulphide (H₂S)
H2S, often from industrial/ agricultural sources, is rated by odour and irritation thresholds unregulated under EU ambient-air law and not routinely monitored. However, short-term exposure above 5 ppb can cause irritation and should be investigated where industries emit it.
6.5 Carbon Monoxide (CO)
CO, a product of incomplete combustion, reduces oxygen transport in blood. Ireland adheres to the EU limit of 10 mg/m³ averaged over 8 hours to prevent acute health effects .
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