1. Comparison of three photochemical mechanisms (CB4, CB05, SAPRC99) for the Eta-CMAQ air quality forecast model for O 3 during the 2004 ICARTT study Shaocai Yu $,&, Golam Sarwar +, Rohit Mathur +, Daiwen Kang $,&, Daniel Tong $,&, & Atmospheric Modeling Division, ARL, NOAA, RTP, NC 27711. $ On assignment from Science and Technology Corporation, + NERL, U.S. EPA, RTP, NC 27711

3.  CB05 and SAPRC: more species and reactions; better characterization of radical recycling; but need more time

6. Model domain and surface sites (AIRNOW, AIRMAP) AIRMAP sites

7. Tracks of (a) P-3, (b) DC-8 P-3 DC-8 P-3: Northeast ; DC-8: Eastern US

8.  Results: Max 8-hr O 3 at AIRNOW sites  Very close

9.  Results : O 3 Vertical profiles (7/14-8/15) Models reproduced vertical structure of Obs P3: SAPRC99>CB05>CB4>Obs DC-8: similar to P3 although slightly close to Obs (1) P-3 Daily Layer Means Height (m)

10.  Results : CO and HNO 3 Vertical profiles (7/14-8/15) CO:  Consistent Underpredictions. ëpartly due to inadequate representation of biomass burning effects from outside the domain ëObs>CB05~CB4>SAPRC Daily Layer Means HNO 3 :  Very good  Slight underprediction (1) P-3 Conc. (ppb) Height (m)

11.  Results : NO 2 and NO Vertical profiles (7/14-8/15) NO 2 :  P3: good at high altitudes  Underestimate at lower altitudes  Organic nitrate can react back to NO 2 in CB05 and SAPRC Daily Layer Means NO:  Under predictions of NO ëAircraft and lightning NO emissions are not in inventory

12.  Results : NO y, SO 2, H 2 O 2 Vertical profiles (7/14-8/15) NO y,  Consistent overestimation SO 2 : Overestimation at low altitudes but good at high altitudes Daily Layer Means H 2 O 2 :  CB4: significant overestimation  Its H 2 O 2 formation rate is 62% higher than CB05 (Luecken et al., 2008)  CB05 and SAPRC: close to Obs  CB05: slightly higher than Obs  SAPRC: slightly lower than Obs CB05 produces more new HO 2, enhancing H 2 O 2

13.  Results : Time-series evaluation on ship  Gas species (NMB,%) CB4CB05SAPRC O3O3 24.436.542.3 O 3 +NO 2 21.532.237.9 CO-4.3-7.4-13.3 NO y 43.337.616.4 NO 2 -6.2-13.9-10.2 NO-30.6-46.9-46.4 PAN28.624.6-11.3 SO 2 68.482.085.6 ISOP-61.3-58.7-60.7 Slightly better:  CB4: O 3, CO, NO 2, NO, SO 2  CB05: Isop  SAPRC: NOy, PAN O3O3 NO y NO 2 NO PAN SO 2 Isoprene CO O 3 +NO 2

14.  Results : Time-series data on ship O 3 production efficiency (  N )  O 3 -NOz slope ( Olszyna et al., 1994 ): Upper limit of  N  SAPRC>CB05>CB4 but all are lower than Obs ë Consistent with O 3 concentrations

15.  Results 2. Time-series evaluation at AIRMAP sites Castle Springs (CS) O3O3 NO y NO CO SO 2 High O 3 period (721-7/23) Low O 3 period (724-7/27) NO 2

16.  Results 2. O 3 production efficiency at AIRMAP sites (O 3 -NO z slope)

17.  N  O 3 -NOz slope : Upper limit of  N  SAPRC>CB05>CB4 but all are lower than Obs ë Consistent with O 3 concentrations ë SAPRC is close to Obs

18. Contacts: Brian K. Eder email: eder@hpcc.epa.gov www.arl.noaa.gov/ www.epa.gov/asmdnerl

19. Contacts: Brian K. Eder email: eder@hpcc.epa.gov www.arl.noaa.gov/ www.epa.gov/asmdnerl

21. CBMIV (Operational) vs. CB05 (experimental) performance Max 8-hr O 3, CONUS, June 15-Aug. 31, 2008 Lower bias and error with CB05 at moderate-high O 3 mixing ratios Higher error in regional statistics due to over-prediction at low mixing ratio range - Could it be for reasons other than chemical mechanism?

22.  Results 7/19/04 7/18/047/17/04 July 16-22, 2004: Evidence of effects of long range transport (Alaskan fire) (1) MODIS (satellite) observations for AOD (2) TOMS (satellite) observations for absorbing aerosol index  Significant underpredictions of PM 2.5 by the model during July 16 to 26 are mainly due to inadequate representation of biomass burning (carbonaceous aerosol) effects from outside the domain (Alaskan fire)