Eta-CMAQ air quality forecasts for O<sub>3</sub> and related species using three different photochemical mechanisms (CB4, CB05, SAPRC-99): comparisons with measurements during the 2004 ICARTT study

Abstract

Abstract.A critical module of air quality models is the photochemical mechanism. In this study, the impact of the three photochemical mechanisms (CB4, CB05, SAPRC-99) on the Eta-Community Multiscale Air Quality (CMAQ) model's forecast performance for O 3 , and its related precursors has been assessed over the eastern United States with observations obtained by aircraft (NOAA P-3 and NASA DC-8) flights, ship and two surface networks (AIRNow and AIRMAP) during the 2004 International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) study. The results show that overall none of the mechanisms performs systematically better than the others. On the other hand, at the AIRNow surface sites, CB05 has the best performance with the normalized mean bias (NMB) of 3.9%, followed by CB4 (NMB=−5.7%) and SAPRC-99 (NMB=10.6%) for observed O 3 ≥ 75 ppb, whereas CB4 has the best performance with the least overestimation for observed O 3 < 75 ppb. On the basis of comparisons with aircraft P-3 measurements, there were consistent overestimations of O 3 , NO z , PAN and NO y and consistent underestimations of CO, HNO 3 , NO 2 , NO, SO 2 and terpenes for all three mechanisms although the NMB values for each species and mechanisms were different. The results of aircraft DC-8 show that CB05 predicts the H 2 O 2 mixing ratios Correspondence to: S. Yu (yu.shaocai@epa.gov) most closely to the observations (NMB=10.8%), whereas CB4 and SAPRC-99 overestimated (NMB=74.7%) and underestimated (NMB=−25.5%) H 2 O 2 mixing ratios significantly, respectively. For different air mass flows over the Gulf of Maine on the basis of the ship data, the three mechanisms have relatively better performance for O 3 , isoprene and SO 2 for the clean marine or continental flows but relatively better performance for CO, NO 2 and NO for southwesterly/westerly offshore flows. The results of the O 3 -NO z slopes over the ocean indicate that SAPRC-99 has the highest upper limits of the ozone production efficiency (ε N ) (5.8), followed by CB05 (4.5) and CB4 (4.0) although they are much lower than that inferred from the observation (11.8), being consistent with the fact that on average, SAPRC-99 produces the highest O 3 , followed by CB05 and CB4, across all O 3 mixing ratio ranges

Evaluation of simulated photochemical partitioning of oxidized nitrogen in the upper troposphere

“…Also, ensure that the chemical mechanism used accounts for PAN photolysis and near-IR HO 2 NO 2 photolysis. Photolysis is the dominant PAN chemical loss process in the upper troposphere, where many have reported PAN overprediction (Pickering et al, 2009;Yu et al, 2010;Fang et al, 2010).…”

A comparison of atmospheric composition using the Carbon Bond and Regional Atmospheric Chemistry Mechanisms

“…Predictions on other days also show similar agreement with observed data. Previous studies (Yu et al, 2010(Yu et al, , 2012 comparing model predictions obtained with CBIV and CB05 mechanisms to observed PAN from several field campaigns have also noted that these mechanisms overpredict PAN. Thus, the chemistry in RACM2 has improved the predictions of PAN.…”

Evaluating the capability of regional-scale air quality models to capture the vertical distribution of pollutants

“…Some specific experimental (e.g. Cros et al, 2004;Drobinski et al, 2007;Yu et al, 2007Yu et al, , 2010Tang et al, 2011) or case studies (e.g. Emeis et al, 2011;Matthias et al, 2012) using upper-level measurements do exist, but comprehensive tropospheric evaluation and model inter-comparisons over long time periods are missing.…”