Characteristics of Common Ions in Atmospheric Fine Particles in Guangzhou and Their Influential Factors

Objectives  To evaluate the characteristics of water soluble inorganic ion in atmospheric PM_2.5 and their influential factors.

Methods Daily PM_2.5 samples were collected in Guangzhou from 2015 to 2016. The level of water soluble inorganic ion (Cl^-, NO₃^-, SO₄^2- and NH₄⁺) in PM_2.5 were examined with ultrasonic extraction and ion chromatography. The association between the level of daily common ion and their influential factors, such as temperature, relative humidity, precipitation and the source of airstream within 24 h, was analyzed by a multiple linear regression method. Seasonal characteristics of common ions based on the average level and time series were analyzed.

Results  The average level of PM_2.5 was 63.3 μg/m³, and the average level of Cl^-, NO₃^-, SO₄^2- and NH₄⁺ were 0.99, 5.75, 9.19 and 4.61 μg/m³, respectively. The common ions in air were derived mainly from industrial emission. The washout effect of rainfall was the most important factor for the daily level of NO₃^-, SO₄^2- and NH₄⁺, while the "weekends" was the most important factor for daily Cl-level. The levels of common ions were higher in dry seasons and they were lower in wet seasons; different ions had their own characteristics.

Conclusions  Based on the seasonal variations of precipitation and other factors, common ion levels were high in dry seasons; and long-term control measures should be planned to obtain better air quality.