Distribution characteristics of air ions and their relationship with environmental factors in Xi´an

An investigation of distribution and variation of air ions is essential to understand the factors that affect air conductivity and aerosol formation. The concentration of negative air ions (NAIs) was measured at 16 sampling sites in Xi´an city from August 2009 to July 2010. At the same time, environmental factors were also monitored such as temperature, relative humidity, wind speed and concentration of inhalable particulate matter (PM₁₀). The spatial-temporal distribution characteristics of NAIs were then determined. Moreover, the relationships between the concentration of NAIs and environmental factors were analyzed in detail. Finally, influence mechanism of environmental factors was discussed based on the theory of atmospheric ionization and diffusion. The observation results show that both spatial and temporal distributions of NAIs are uneven. Spatially the concentration of NAIs increases from city center to suburb. The average concentration of NAIs is in the range 200 ~ 300 cm^-3 in urban, while more than 500 cm^-3 in the suburb. Over a year the concentration of NAIs is highest in summer and lowest in winter. The positive correlations have been found between the concentration of NAIs and the temperature and relative humidity, while negative correlation has been found between the concentration of NAIs and PM₁₀.