表 2.

2014—2017年兰州市气象因素各指标和空气污染物的描述性分析

Descriptive statistics for meteorological variable and air pollutant levels in Lanzhou during 2014 to 2017

Category	x±s	Minimum	Percentile			Maximum
			P 25	P 50	P 75
PM, particulate matter.
Meteorological factors
Temperature/℃	11.28±9.64	-12.30	2.45	12.90	19.80	29.90
Relative humidity/%	50.83±15.15	18.00	39.00	50.02	61.74	96.09
Air pollutants
PM2.5/(μg/m3)	53.30±27.19	12.73	35.40	45.69	63.59	269.43
PM10/(μg/m3)	122.90±78.25	18.98	81.00	107.94	145.25	1484.54
SO2/(μg/m3)	22.39±14.47	3.54	10.88	18.29	30.42	81.87
NO2/(μg/m3)	45.98±15.74	7.80	36.40	45.36	52.90	146.60
CO/(mg/m3)	1.34±0.73	0.34	0.83	1.09	1.62	4.65