Investigating and optimizing a method to determine atmospheric mercury for application in Ho Chi Minh City, Viet Nam

Abstract

Mercury (Hg) is a toxic of global concern due to its bioaccumulation in the environment and the atmosphere which is an important environment in the biogeochemical cycle of Hg. IO-5 method (US-EPA) is the most common analysis method to measure the concentration of atmospheric Hg. However, few studies have been done in tropical monsoonal areas such as Ho Chi Minh City (HCMC). This paper reported the investigation and optimization of the IO-5 method for WA-5F, NIC with the purpose of measuring the atmospheric Hg in Ho Chi Minh City as well as other tropical monsoon regions. The sampling temperature of gold trap, sampling flow rate and time, use of soda lime, passive Hg infection over time, and concentration repeatability were investigated. The results showed that the NIC gold trap was in good stability with recoveries (H%) always higher than 95% for temperatures of 30‒150oC. Because of the tropical climatology in HCM City, a heater for the gold trap was not necessary. The recoveries were > 95% for sampling rates of 0,3‒2,5 L/min. A sampling rate of 0,5 L/min for 12‒24 hours sampling periods as well as a soda lime trap to protect the gold trap during sampling were recommended. Testing the gold traps blank showed a negligible passive contamination after 30 days of storage, demonstrating the suitability of the procedure for long-term sampling campaigns. In addition, the average difference in the Hg concentration between two parallel samples was less than 10%, consistent with standards from the professional monitoring networks worldwide. In general, applying the IO-5 method in monitoring the atmospheric Hg in HCM City was suitable. Moreover, the obtained result offered a suitable method to collect the atmospheric Hg data in Vietnam as well as in Southeast Asia where the anthropogenic Hg monitoring data were limited.