# Impact of the new dry deposition in CMAQ v5.4 on coarse PM **URL:** \ **Category:** CMAQ\ **Tags:** cmaq\ **Created:** [January 31, 2025, 11:40am UTC](https://forum.cmascenter.org/t/impact-of-the-new-dry-deposition-in-cmaq-v5-4-on-coarse-pm/5557 "2025-01-31T11:40:19Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![bkoo](https://avatars.discourse-cdn.com/v4/letter/b/2acd7d/32.png) [@bkoo](https://forum.cmascenter.org/u/bkoo)\ **Post date:** [January 31, 2025, 11:40am UTC](https://forum.cmascenter.org/t/impact-of-the-new-dry-deposition-in-cmaq-v5-4-on-coarse-pm/5557/1 "2025-01-31T11:40:19Z")
After updating our modeling platform from CMAQ `v5.3.1` to `v5.4`, we noticed that coarse mode sea salt concentrations were much lower with the new CMAQ version. So, we conducted some test runs, and the results are summarized in the slides linked here: [Dropbox](https://www.dropbox.com/scl/fi/m7gq9rz4ub3vmfqun4y0n/Coarse_PM_Deposition_Test.pptx?rlkey=seauaccvooh9a8yp9u7yv566x&st=37a87usp&dl=0) This issue is similar to what’s reported in this thread: [Low PM10 in CMAQv5.4](https://forum.cmascenter.org/t/low-pm10-in-cmaqv5-4/3957) Unlike what’s reported there, however, we observed that turning on the `AERO_M2USE` options didn’t make much impacts. Here are our findings: - Pleim et al. ([https://doi.org/10.1029/2022MS003050](https://doi.org/10.1029/2022MS003050)) stated “[t]he most significant effect of the new model is to increase the mass dry deposition of the accumulation mode aerosols in CMAQ.” However, our test shows that differences between `v5.3.1` and `v5.4` are much larger in `ASEACAT` than in `ANAJ` (slide 3). The slide also shows that switching on the `AERO_M2USE` options made little difference on the modeled concentrations. - Slides 4-5 show process changes at the grid cell calculated by the IPR analysis. Both `v5.3.1` and `v5.4` show similar net process changes for `ANAJ`. For `ASEACAT`, however, a huge loss due to dry deposition (largely compensated by vertical diffusion) occurs during the first hour of the simulation with `v5.4`, which results in initial concentration drop shown in the bottom plot of slide 3. This seems unrealistic. - We also looked at other coarse PM components: `ASOIL` and `ACORS` (slides 7-9). `ASOIL` shows an initial concentration drop with `v5.4` similar to `ASEACAT`. Its IPR result also shows a big dry deposition loss with `v5.4` like `ASEACAT`. However, `ACORS` does not show such anomalies. This is strange; perhaps it has something to do with different size distributions among these coarse PM species? My main concern is the huge difference in `ASEACAT` between `v5.3.1` and `v5.4` (this has a big impact on our sea salt model performance with the new modeling platform). Is this expected with the new dry deposition model? I’d appreciate any insight/suggestion on this issue and will provide more details about our tests if needed. Thanks! ---
**Author:** ![pleim.jon](https://avatars.discourse-cdn.com/v4/letter/p/4bbf92/32.png) [@pleim.jon](https://forum.cmascenter.org/u/pleim.jon)\ **Post date:** [February 10, 2025, 9:13pm UTC](https://forum.cmascenter.org/t/impact-of-the-new-dry-deposition-in-cmaq-v5-4-on-coarse-pm/5557/2 "2025-02-10T21:13:11Z")
There are many differences in aerosol dry deposition velocity between CMAQv5.3.1 and v5.4. The Pleim et al. 2022 paper shows these. To better understand the effects in your runs, you should compare the aerosol deposition velocities VMASSI, VMASSJ and VMASSC for Aitken, accumulation and coarse mode, respectively. Note that all aerosol species use these same deposition velocities. ---
**Author:** ![bkoo](https://avatars.discourse-cdn.com/v4/letter/b/2acd7d/32.png) [@bkoo](https://forum.cmascenter.org/u/bkoo)\ **Post date:** [February 13, 2025, 9:03am UTC](https://forum.cmascenter.org/t/impact-of-the-new-dry-deposition-in-cmaq-v5-4-on-coarse-pm/5557/3 "2025-02-13T09:03:24Z")
Thanks @pleim.jon for your response! Following your suggestion, I compared `VMASSJ` and `VMASSC` between `v5.3.1` and `v5.4` (see below). `v5.3.1` and `v5.4` calculate comparable `VMASSJ` (with `v5.3.1` showing somewhat higher peaks) whereas `VMASSC` is significantly higher with `v5.4` throughout the simulation. This is consistent with what the concentration plots show on slide #3 of the PPT attached to the OP. However, this seems to contradict what Pleim et al. (2022) says, that is, the main impact of the new model is on the accumulation mode. Perhaps, the assessment was based on comparison of deposition velocities for vegetated areas. The grid cell (55, 100) for my plots is located in a developed area (39% Developed Medium Intensity; 23% Developed Low Intensity; 20% Developed High Intensity; 13% Developed Open Space). Pleim et al. (2022) states that for accumulation mode, the effects of the new model are minor in developed areas compared to those in heavily forested areas (Figure 9d in the paper), but doesn’t mention what they look like for coarse mode. I wonder if the large increases in `VMASSC` with `v5.4` is consistent with the expected outcome of the new dry deposition model. Hope you can shed some light on this. Thanks! ![VMASS](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/f/f167b031745982b38c12a2c2a8c58420943edc3d.png) ---
**Author:** ![pleim.jon](https://avatars.discourse-cdn.com/v4/letter/p/4bbf92/32.png) [@pleim.jon](https://forum.cmascenter.org/u/pleim.jon)\ **Post date:** [February 18, 2025, 9:56pm UTC](https://forum.cmascenter.org/t/impact-of-the-new-dry-deposition-in-cmaq-v5-4-on-coarse-pm/5557/4 "2025-02-18T21:56:36Z")
For the runs that we have made for evaluation, in general, the change in aerosol dry deposition from v53 to v54 is greater for accumulation mode than for coarse mode. This may not be true for every grid cell in every application. One reason the increase dry deposition is especially large in urban areas is that we have added factor on the boundary layer resistance to represent the greater surface area for deposition on city buildings. Note that there is also a large dependence on the geometric mean diameters and the geometric standard deviations of each mode. The coarse mode is even more sensitive to these parameters because deposition velocities increase rapidly toward larger diameters. ---
**Author:** ![bkoo](https://avatars.discourse-cdn.com/v4/letter/b/2acd7d/32.png) [@bkoo](https://forum.cmascenter.org/u/bkoo)\ **Post date:** [February 26, 2025, 12:09am UTC](https://forum.cmascenter.org/t/impact-of-the-new-dry-deposition-in-cmaq-v5-4-on-coarse-pm/5557/5 "2025-02-26T00:09:46Z")
Thanks for pointing out the factors affecting dry deposition. I did a quick sensitivity run with building area index (BAI) set to 1 everywhere, and it made little impact on the results. So, I guess that’s not the cause. Then, I compared geometric mean diameter and geometric standard deviation between `v5.3.1` and `v5.4` (see below). The two models show comparable diameters, but quite different standard deviations: the standard deviations calculated by `v5.4` are drastically higher than those by `v5.3.1`, often hitting the upper limit. I believe this causes the large discrepancies in `VMASSC` shown above. I’m kinda surprised to see that the two models predict such different standard deviation values despite using consistent inputs. What changes (updates) in `v5.4` could possibly contribute to this? Can someone provide an explanation? Thanks! ![Coarse_PM_Deposition_Test_DG_STDEV](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/c/cd2815ba4146b95c7bb2a25789989942d36d3b0c.png)