CTM	chemical transport model
MLR	multiple linear regression
ARIMA	integrated moving average model
GRNN	general regression neural network
LSSVM	least squares support vector machine
SVM	support vector machine
AHP	analytical hierarchical process
EMD	empirical mode decomposition
EEMD	ensemble empirical mode decomposition
CEEMD	complementary ensemble empirical mode decomposition
IMF	intrinsic mode function
DE	differential evolution
BBO	biogeography-based optimization
PDF	probabilistic distribution function
CDF	cumulative distribution function
AW	average width
CP	coverage probability
AQI	air quality index
MAE	mean absolute error
MAPE	mean absolute percentage error
RMSE	root mean square error
R2	goodness of fit
Std.	standard deviation