Relationship between Meteorological Factors and Air Quality in Xi'an City

Objective By means of an analysis on air pollution index and meteorological factors from November 1st, 2013 to October 31st, 2014 in Xi'an, to comprehensively reveal the relationship between meteorological factors and air pollutants.

Methods Using statistical description to analyze the effect of meteorological factors, such as temperature, air humidity, wind speed, air pressure and rainfall on air pollutant index, such as AQI indices, PM_2.5, PM₁₀, SO₂, NO₂, and CO. A canonical correlation method was used to obtain four pairs of typical variables for the correlation between air quality indices (W) and meteorological factors (V); then the relationship between the current status of air quality and meteorological factors was explored.

Results Based on the average annual value of grade Ⅱ standard limit set in the Environmental air quality standard (GB 3095-2012), ① the average annual concentrations of PM_2.5 and PM₁₀ were higher than the standard limit, CO and SO₂ reached the grade Ⅱ standard limits, while NO₂ was slightly higher than the grade Ⅱ standard limit in Xi'an. ② The change of air pressure was smoothly, the average monthly humidity was about 70%, the wind speed was relatively stable throughout the year, and the rainfall were low in winter and spring, slightly higher in summer, and obviously increased in autumn. ③ Simple correlation analysis shows the correlation coefficient between temperature and AQI, PM_2.5, PM₁₀, CO, NO₂ and SO₂ were more than 0.5; the correlation coefficient between air humidity and SO₂ was higher than others; the correlation coefficient between wind speed and NO₂ was 0.5; the correlation coefficients among air pressure and SO₂, NO₂ and CO were more than 0.5. The correlations of rainfall with AQI, PM_2.5, PM₁₀, CO, NO₂ and SO₂ were significant, too. ④ Canonical correlation analysis shows there was a relationship between meteorological factors and air quality; temperature has a major effect on concentration of gaseous pollutants; humidity has a major effect on concentration of PM_2.5; wind speed has a major effect on concentration of NO₂; and rainfall has main influence on concentration of particulate pollutants.

Conclusion During the study, there was a correlation between air quality and meteorological factors in Xi'an.