## 5 Conclusions  
The AQI has been used around the world for many years, yet its intrinsic limitations are increasingly apparent. A sharp boundary leads to completely different evaluation results and corresponding measures facing almost the same air quality. A biased evaluation is not objective and comprehensive enough, and a conservative strategy may exaggerate actual air pollution and bring about unnecessary economic loss and public concern. In addition, incomplete criteria have caused questionable evaluation results. Now people are beginning to realize the inconsistency between their feelings and reports of AQI, and meanwhile governments are also considering how to balance air pollution control and economic development. Therefore, based on the comparative analysis of AQI in theory, we designed a novel air quality evaluation paradigm, the AQFCE, which consists of preprocessing, evaluation and early warning. To ensure the integrity and accuracy of data, least square piecewise polynomial fitting and linear regression was used for missing and reversal data of air pollutant concentration in the preprocessing module. In the evaluation module, membership degree is adopted to deal with the problem of a sharp boundary. Compared with the biased evaluation and  
Figure 8: Hourly pollutant concentration variation and air quality evaluation result of chief pollutant and level of Xi’an. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Beijing**} & \multicolumn{3}{c}{**Shanghai**} & \multicolumn{3}{c}{**Xi’an**} \\ \cline{2-11}  & \multicolumn{2}{c}{**DR**} & \multicolumn{2}{c}{**HR**} & \multicolumn{2}{c}{**DR**} & \multicolumn{2}{c}{**HR**} & \multicolumn{2}{c}{**DR**} & \multicolumn{2}{c}{**HR**} \\ \cline{2-11}  & **CP** & **Level** & **CP** & **Level** & **CP** & **Level** & **CP** & **Level** & **CP** & **Level** & **CP** & **Level** \\ \hline AQI and AQFCE & 82.4\% & 58.08\% & 63.04\% & 45.49\% & 85.48\% & 48.77\% & 47.59\% & 58.74\% & 83.84\% & 50.96\% & 69.88\% & 25.68\% \\ AQI* and AQFCE & - & - & 89.74\% & 97.39\% & - & - & 84.76\% & 96.99\% & - & - & 89.94\% & 94.99\% \\ \hline \multicolumn{11}{c}{CR (T): Consistent Rate (Kendall Correlation Coefficient), DR/HR: Daily Report/Hourly Report, CP: Chief Pollutant, AQI*: exclude PM\({}_{2.5}\) and PM\({}_{10}\) in HR.} \\ \end{tabular}
\end{table} 
Table 5: The comparison of evaluation result between the Air Quality Index (AQI) and Air Quality Fuzzy Comprehensive Evaluation (AQFCE) by consistent rate (CR) (T). conservative strategy of the AQI, a principal factor prominent model \(M(\bullet,\vee)\) based on the membership degree and factor weight of all pollutants can give more objective evaluation results and balance human health protection and pollution control cost. A complete and targeted calculation grid based on scientific evidence is proposed too. Moreover, the early warning module can provide timely alerts and recommended measures according to the evaluation results of air quality. In general, the AQFCE can achieve an air quality evaluation and forecast at different time scale. Comparative analysis of the AQI and AQFCE in practice was carried out in China under various conditions including different space (Beijing, Shanghai and Xi'an), time (autumn, winter, spring and summer), task (daily report, hourly report) and purpose (chief pollutant, level). Experimental results offer some meaningful information:  
1. Referring to actual pollutant concentration, the AQFCE accurately reflects the trend of air pollution under different pollution conditions (lighter pollution, heavier pollution, pollution process) and is sensitive to sudden and significant changes in concentration. In daily reports, the AQFCE and AQI have high consistent rates and correlation coefficients regarding the chief pollutant and level, respectively, in Beijing, Shanghai and Xi'an, while examples prove the AQFCE with a comprehensive strategy is more reasonable than the AQI with a conservative strategy.