1 / 20

Orographic Enhancement of sulphur and nitrogen wet deposition in Models-3

Orographic Enhancement of sulphur and nitrogen wet deposition in Models-3. Ray Wright & Paul Sutton RWE npower Windmill Hill Business Park, Swindon, UK This work is funded by the Joint Environment Programme. Introduction.

zora
Download Presentation

Orographic Enhancement of sulphur and nitrogen wet deposition in Models-3

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Orographic Enhancement of sulphur and nitrogen wet deposition in Models-3 Ray Wright & Paul Sutton RWE npower Windmill Hill Business Park, Swindon, UK This work is funded by the Joint Environment Programme

  2. Introduction • Requirement for accurate modelling of: pollutant gases and particles, and acid deposition, in accordance with increased industrial activity and the consequent increased need for regulation – from all industrial, domestic, agricultural and natural sources. • Models-3 (“CMAQ”) has been in use for several years and has been show to reproduce acid deposition measurements in the UK to an acceptable extent • Room for further improvement?

  3. Does M3 give a good representation of sulphate and nitrate deposition? • Previous JEP work involving monitoring network indicated good agreement between measurements and model predictions (Cocks, Lucas Rodgers & Teasdale, The performance of Models-3 for Deposition and Atmospheric Concentrations over a year, 2003)

  4. Annual comparison: precipitation

  5. Annual comparison: wet deposition of S

  6. Annual comparison: wet deposition of oxidised N

  7. Models-3 compared with measurement Annual means are good, individual sites good, except for ammonia

  8. Terrain heights

  9. UK rainfall 1999 from UM (non-convective)

  10. Locations of monitoring sites

  11. Does M3 give a good representation of sulphate and nitrate deposition? • From comparison with the existing monitoring network - YES • But there could be precipitation on higher sites that M3 is missing (No sites in Snowdonia, Scotland)

  12. Models-3 seems to have all the needed processes, but does it? • Observations show enhanced wet deposition of sulphate and nitrate on high ground (Great Dun Fell campaign) • Not all of it is due to higher precipitation • High conversion rate to sulphate and nitrate in cloud. • Seeder-feeder process? • Occult deposition process? • What’s in Models-3?

  13. Seeder-feeder and occult deposition

  14. Concentration (Nitrate aerosol) If precipitation is high in bottom layer, due to seeder-feeder mechanism, then we should get high S & N deposition

  15. Investigated Models-3 “resolved cloud” module • Contrary to Models-3 documentation, the layer heights are not being used to apportion rain water to layers (e.g deeper layers should contain more water) • Tried code modification with layer heights put in • A cloud-presence threshold is in Models-3. If cloud water is below threshold, no chemistry is carried out (also discovered by Mueller & Cook, TVA, Alabama, USA. They noticed that M3 does not reproduce cloud cover fractions well) • Tried code modification by applying threshold to the summation of Qr over all layers

  16. Results of tests B007 – Original code case B009 – Layer height variation applied B010 – Threshold code change applied B011 – Both changes applied Domain is UK 6km, for JEP studies

  17. Initial conclusions from tests • Sulphate and nitrate deposition increased by taking layer heights into account • Applying threshold to summation of rain water over all layers results in substantial general increase in sulphate and nitrate deposition • Need to check effect of (just) lowering threshold (As Mueller and Cook did)

  18. What about the seeder-feeder mechanism? • Seeder-feeder mechanism is represented in MM5 and UM rainfall calculations (according to consultation) • Difference in MM5 and UM output fields may result in Models-3 NOT seeing heightened precipitation in bottom layer due to fixed apportioning. UM only outputs Q(Liquid) • Q(Cloud) = 0.85 x Q(Liquid) and Q(Rain) = 0.15 x Q(Liquid) • When Seeder-Feeder is operating, Q(Cloud) will be smaller and Q(Rain) will be larger in the bottom layer (This info does not end up in Models-3 unless we use MM5, WRF, etc), so, maybe, M3 would underestimate precipitation in bottom layer in this case.

  19. What about occult deposition? • Other work has shown that up to 50% of sulphate and nitrate deposition on high ground can come from occult deposition (Wrzesinsky et al. 2001, Thalmann et al. 2002) • Water deposition due to wetting by fog accounts for only ~ 10% of total deposition on high ground, BUT • Cloud (fog) water S & N concentrations much greater than in rain water (x5 or more) • So, occult deposition can account for 50% of deposition, depending on vegetation type • We can add this process to Models-3, internally.

  20. Conclusions • Cloud & rainfall in Models-3 not optimally handled, but can be addressed • Seeder-feeder mechanism in meteorological models, but may not fully appear in Models-3, depending on which model is used. • Occult deposition not represented, but could be introduced. • N.B. need more measurement sites on high ground to check.

More Related