Measurements and model results confirm that when PM concentrations are high, the contribution of sea salt to PM is less than the averaged annual contribution. In these cases, subtraction of the sea salt contribution appears to have no or hardly any effect on the incidence of PM10 limit value exceedances. Whether current national regulation regarding sea salt needs updating, is subject to further analysis.
Sea salt contribution to particulate matter in the Netherlands is small when PM concentrations are high
Research on the contribution of sea salt to PM10 and PM2.5
Sea salt aerosol makes a natural contribution to particulate matter (PM10), and cannot be influenced by abatement strategies. In the Netherlands the sea salt contribution is subtracted from PM10 according European regulations when checking compliance to PM10 limit values. The report has improved the so-far limited knowledge on sea salt and its contribution to PM10 and PM2.5 in the Netherlands. We focused on one year of sodium measurements, which is a good indicator for sea salt, and combined these with results from the LOTOS–EUROS model, which describes the generation and transport of sea salt aerosol.
Contribution sea salt very variable
Average concentrations over the observation period varied from 4 μg/m³ close to the coast in Rotterdam, to 2 μg/m³ land inwards, in Vredepeel. Average daily concentrations, sometimes, would be much higher or much lower. When, for PM10, the European limit vale of 50 μg/m³ was exceeded, the contribution of sea salt aerosol, generally, was less than the average annual concentration. Because contributions of sea salt to PM10 and PM2.5 vary strongly from day to day, and also from year to year, our conclusions from the one-year observation period cannot simply be extrapolated onto other years. Therefore, we recommend that the current analysis is extended with routine sodium measurements, which recently have started in the National Air quality Monitoring Network, and combined with model calculations.
The study was carried out by TNO in cooperation with the ECN, the RIVM and the PBL as part of the Netherlands Research Program on Particulate Matter (BOP).