《Table 1–Evaluation parameters during two study periods.》

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《"A monitoring-modeling approach to SO_4~(2-) and NO_3~- secondary conversion ratio estimation during haze periods in Beijing, China"》

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Simulated hourly PM2.5concentrations and daily SO42-and NO3-concentrations were compared to the observations measured by this study to evaluate the performance of the modeling system in the present work.Table 1 presents a comparison of modeling results and monitored data during the two study episodes.For total PM2.5，the correlation coefficient（RC）values of the twoperiods were 0.92 and 0.78，demonstrating good correlations during both episodes.However，the simulated concentrations were underestimated，especially during heavy haze periods.For example，the peak value of hourly concentration reached385.3μg/m3while the simulated value was only 140.3μg/m3.Daily simulated results of the two components during the studyperiods showed similar trends as the observation data.SO42-and NO3-of Episode 1 were underestimated，with average concentrations of 14.9 and 19.3μg/m3for simulation，17.4 and 25.6μg/m3for observation.However，they were overestimated during Episode 2with the average concentrations of 12.4 and 33.7μg/m3for simulation，while 8.1 and 31.6μg/m3for observation.These deviations could be explained by the following reasons:（1）There is a lack of consideration of secondary component reactions and the deviation of the reaction coefficient by the modeling system which could lead to an underestimation of simulation results；（2Extremely strict control measurements were taken in Beijing and its surrounding cities，especially in 2017，in order to achieve the target concentrations，and there is uncertainty in the emission reduction for various pollutants.Simulated meteorological parameters，including wind speed (WS）and temperature（T），were also compared to monitored data.Although overestimation was found for both parameters，RC were also larger than 0.70 during two study periods.Overall，the simulated results were acceptable compared to other studies.