Challenges in PM Measurement and Modelling

1. Working group II Questions related to PM measurement and modelling

2. General remarks • All models underestimate PM concentrations; no mass closure • Large uncertainties in emissions inventories • Need for a better qualification of what is expected from measurements : • too few observations for too many parameters • technical difficulties • monitoring strategy still need to beelaborated in the networks

3. Q7 : How well can we link sources to observed PM levels with atmospheric models • Secondary Inorganic Aerosols (SIA); Sulfate • Emission inventories are rather satisfactory excepted (perhaps) for ships and harbours activities • Measurements are reliable : long experience, high resolution possible • Models give relevant results for atmospheric concentrations, although improvements related to the cloud chemistry are still possible (and encouraged).Deposition is more difficult, especially wet deposition.

4. Q7 : How well can we link sources to observed PM levels with atmospheric models • Secondary Inorganic Aerosols (SIA); Nitrate • Few measurements in Europe, made with filter-based techniques: problem of evaporation still not solved • Good temporal resolution needed considering the processes • How to translate what is on the filter in what is modelled? Numerous and quick reactions involved. • Need for concomitant ammonia, nitric acid, NO2, nitrate measurements for modelling (intensive campaigns) • Sensitivity to the meteorological parameters: temperature, humidity • Issue for ammonia emissions, still inaccurate for agriculture

5. Q7 : How well can we link sources to observed PM levels with atmospheric models Acceptable results for SIA • Measurements : OK • Models : “trustable” • Improvements still possible but not considered as a priority

6. Q7 : How well can we link sources to observed PM levels with atmospheric models EC/OC • No reference method, lack of accuracy and lack of consistency between European measurements. German standard exists but work still needed • Large differences in results issued from different methods • Total carbon could be well estimated but modellers need to know the primary/secondary parts from anthropogenic/biogenic sources • Recommendation : Need for a standard method!

7. Q7 : How well can we link sources to observed PM levels with atmospheric models EC/OC • Emission of primary carbon should be improved : quantities, speciation - wood combustion, residential heating) • Improvements needed to correctly grid the emissions and to get the right temporal profiles • Recommendation : develop levoglucosan measurements (source/receptor approach) and find other tracers • VOC emission and speciation (anthropogenic and biogenic) should be improved for modelling the secondary part

8. Q7 : How well can we link sources to observed PM levels with atmospheric models EC/OC • Obvious and well-known difficulties for modelling: inconsistencies with measurements (but which measurements?) • Complexity of the processes • Developments still needed but they are hampered by the lack of measurement data and emission uncertainties  Finally models are not ready • BUT EC/OC could represent 30 to 50 % of the PM composition!Recommendation : Priority on EC/OC measurement and emission inventories

9. Q7 : How well can we link sources to observed PM levels with atmospheric models Dust/ natural compounds • Measurement of representative compounds : calcium, sodium… : OK • Distinction resuspension and “real” natural sources • Resuspension : soil erosion, traffic • Parametrizations used in the models: uncertainties but global improvement of the results • Sensitivity to weather conditions, accuracy of the land cover needed

10. Q8 : How large are the uncertainties in PM measurements and model? • SIA : • 15-20% for sulfate modelling (annual average) • 40% for nitrate modelling (annual average). Same order of magnitude as the measurement uncertainty • Acceptable • Dust/natural compounds : • difficult to assess • non determinant • EC/OC • (Very) Large uncertainties in measurement, emission inventories and modelling Current models should not be used for IAM and policy purposes related to PM

11. BUT : relevant experiences with PM modelling • Recommendations • Define a “protocole” to check the reliability of the models to represent the right chemical regimes • Consider the models results as absolute values but comparing scenarios : “relative responses” • Need to concentrate measurements at relevant sites: measure all the PM components at the same site, and also gaseous compounds to reach a better understanding of the processes and the chemical regimes

12. Q8 : What improvements are required in PM monitoring, modelling and basic scientific understanding for the assessment of health and climate impacts of PM? • PM measurement : unbearable situation because of the heterogeneity of the measurements in Europe • Recommendation : Use methods which have shown equivalence with the reference method, on a daily basis • PM modelling : Improvement expected for meteorological data and boundary conditions • Better investigation of the urban scale modelling needed (where exposure occurs) • Recommendation : to assess and compare methods available to deal with the urban scale from the regional scale

13. Q8 : What improvements are required in PM monitoring, modelling and basic scientific understanding for the assessment of health and climate impacts of PM? • Promote data assimilation but be aware of the quality of the data assimilated • Promote measurement of vertical profiles (chemical and meteorological) • Recommendation : to measure ad evaluate particulate number and size distribution (for health and climate impact)