# Photolysis of NO2 in SAPRC07 **URL:** \ **Category:** CMAQ\ **Tags:** cmaq\ **Created:** [November 20, 2023, 10:28am UTC](https://forum.cmascenter.org/t/photolysis-of-no2-in-saprc07/4545 "2023-11-20T10:28:50Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Sakura](https://avatars.discourse-cdn.com/v4/letter/s/898d66/32.png) [@Sakura](https://forum.cmascenter.org/u/Sakura)\ **Post date:** [November 20, 2023, 10:28am UTC](https://forum.cmascenter.org/t/photolysis-of-no2-in-saprc07/4545/1 "2023-11-20T10:28:50Z")
Dear CMAQ forum, I am using saprc07tc\_ae6\_aq in CMAQv5.2. In my recent simulation for the summer season, surface ozone concentrations were calculated very low. In that simulation, I used emissions data that had shown reasonable results in the past. I checked PHOTODIAG2 and found that NO2\_06 was almost zero, as shown in the attached. So, I thought that NO2 photolysis was not calculated. Does anyone know about the reason for this NO2\_06 to be zero? Appreciate your kind help. ![NO2_06](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/d/dad06ac94ef343896e70a3e2f50f469d8fe4b603.png) ---
**Author:** ![bhutzell](https://avatars.discourse-cdn.com/v4/letter/b/dfb087/32.png) [@bhutzell](https://forum.cmascenter.org/u/bhutzell)\ **Post date:** [December 5, 2023, 10:05pm UTC](https://forum.cmascenter.org/t/photolysis-of-no2-in-saprc07/4545/2 "2023-12-05T22:05:34Z")
I cannot identify what is causing the problem. Perhaps, examining other variables in the PHOTDIAG1 file may give clues on the cause (such as **COSZENS, ETOT\_SRC\_W381, OZONE\_COLUMN, TRANS\_DIRECT, TAU\_TOT\_W381, TAU\_CLOUD\_w381, TRANS\_DIFFUSE, and AOD\_W381)**. The below plots show possible ranges of their values over the northern hemisphere. ![JNO2](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/8/8f5e5e59218be1fd390a46d00d02d21a878e30cf.png) ![cosine_solar_zenith_angle](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/1/1b53e3a1ad1fb55564219418fcce4198db768fed.png) ![ETOT_Surf_w381](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/c/c6e405451e199320263e21b21e02e6718dbcc2d4.png) ![Total_Ozone_Column](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/5/536283dabb4bc20daab16aff01ee89974cf55083.png) ![Total_Transmissitivity](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/5/54204b28968da03a09ee77e3be2d2b1b4d9ce050.png) ![Tua_Total_w381](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/f/fcc4a68da69729cc16124dc5347d27d257e35056.png) ![Tua_Cloud_w381](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/e/ee7b23f1069c98458b80a2639fa429f6a9caaf0b.png) ![Tua_Aero_w381](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/0/0c10ab94a83f2bc01e8ea6de21a651b72bc0eb1e.png) ---
**Author:** ![cgnolte](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.cmascenter.org/cgnolte/32/53_2.png) [@cgnolte](https://forum.cmascenter.org/u/cgnolte)\ **Post date:** [December 6, 2023, 12:43am UTC](https://forum.cmascenter.org/t/photolysis-of-no2-in-saprc07/4545/3 "2023-12-06T00:43:20Z")
Please post the contents of the CCTM\_v52.cfg file. When you previously obtained reasonable results with this emissions dataset, what version of the model were you using? Do the values of NO2\_O6 increase significantly later in the day, or aloft? ---
**Author:** ![Sakura](https://avatars.discourse-cdn.com/v4/letter/s/898d66/32.png) [@Sakura](https://forum.cmascenter.org/u/Sakura)\ **Post date:** [December 7, 2023, 3:11am UTC](https://forum.cmascenter.org/t/photolysis-of-no2-in-saprc07/4545/4 "2023-12-07T03:11:14Z")
Dear Chris, Thank you for your comment. I am attaching the cfg file. I cannot see any diurnal variation in NO2\_06, but the top level has some value. I used the same V5.2 for the previous calculation. Thank you for your cooperation on it. [CCTM\_v52.cfg.txt](https://forum.cmascenter.org/uploads/short-url/arqMjJ96Vg0VskLbWCE9ftjeBzx.txt) (3.1 KB) ---
**Author:** ![Sakura](https://avatars.discourse-cdn.com/v4/letter/s/898d66/32.png) [@Sakura](https://forum.cmascenter.org/u/Sakura)\ **Post date:** [December 7, 2023, 3:13am UTC](https://forum.cmascenter.org/t/photolysis-of-no2-in-saprc07/4545/5 "2023-12-07T03:13:42Z")
Thank you very much for your very useful advice. I will check it out as soon as possible. I will report back as soon as I find out something. Thank you for your cooperation on it. ---
**Author:** ![cgnolte](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.cmascenter.org/cgnolte/32/53_2.png) [@cgnolte](https://forum.cmascenter.org/u/cgnolte)\ **Post date:** [December 7, 2023, 2:54pm UTC](https://forum.cmascenter.org/t/photolysis-of-no2-in-saprc07/4545/6 "2023-12-07T14:54:52Z")
I have run CMAQv5.4 with the saprc07tc\_ae6\_aq chemical mechanism. That has generated larger values of NO2\_06. CMAQv5.2 was released in June 2017, over 6 years ago. It is difficult to reconstruct a platform on which to test such an old version of the code. Is there a compelling reason why you need to run using version 5.2? ---
**Author:** ![Sakura](https://avatars.discourse-cdn.com/v4/letter/s/898d66/32.png) [@Sakura](https://forum.cmascenter.org/u/Sakura)\ **Post date:** [December 8, 2023, 2:15am UTC](https://forum.cmascenter.org/t/photolysis-of-no2-in-saprc07/4545/7 "2023-12-08T02:15:28Z")
Thank you for your comment on it. I understand that upgrading the version may be one of the quickest solution. I wanted to perform the long term calculation under the same conditions as much as possible without changing the calculation environment. I will consider upgrading the CMAQ in the future.