AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Using Single Particle Levitation Coupled with Raman Spectroscopy to Investigate the Displacement of Ammonium from Aerosol Particles by Uptake of Triethylamine
Yong J. Li, Berto Lee, CHAK K. CHAN, Hong Kong University of Science and Technology
Abstract Number: 233 Working Group: Instrumentation and Methods
Abstract The volatile characteristic of nitrate can result in multiple-mode distribution in the presence of coarse particles due to re-partitioning from fine particles to gas phase, followed by chloride depletion or reactions with crustal aerosols (Zhuang et al. 1999; Yao et al. 2001). The multiple-mode distribution of nitrate may influence nitrate measurements due to different inlet size-cuts used among different instruments. Here we present measurement results of particulate nitrate by AMS and MARGA at a coastal site in Hong Kong. While most of other species showing reasonable agreements between the two instruments, nitrate measurements had a large discrepancy, with the largest discrepancy during daytime. We used several parameterization methods to estimate the partitioning coefficient (K$_p=p$_(NH3)×p$_(HNO3)) of ammonium nitrate, from temperature dependent (solid only) (Mozurkewich 1993), T-relative humidity dependent (solid/liquid) (Mozurkewich 1993), to T-RH-ionic strength (Y=n$_(NO3)/(n$_(NO3)+3n$_(SO4))) (Seinfeld and Pandis 2006) dependent estimations. Results showed that even with T, RH and Y taken into account (lowest K$_p), gas-particle equilibrium could not be reached based on measured NH$_3 and HNO$_3 by MARGA. The product of total ammonium and total nitrate were compared with K$_p=f(T, RH, Y). It is deduced that equilibrium was reached during nighttime, but still not daytime. It is possible that daytime re-partitioning of nitrate is more prominent and shifts the nitrate to the larger sizes by heterogeneous reactions. These results suggest that the multi-mode distribution of nitrate has a strong effect on the real-time measurements of nitrate.
References
Mozurkewich, Atmos Environ a-Gen, 27, 261-270, 1993.
Seinfeld et al.: Atmospheric chemistry and physics: From air pollution to climate change, 2nd ed., Wiley, New Jersey, 2006.
Yao et al., Environ. Sci. Technol., 35, 600-605, 2001.
Zhuang et al., Atmos. Environ., 33, 843-853, 1999.
Acknowledgement
This work was supported by the University Grants Committee (SEG-HKUST07) and the Environmental Conservation Funds of Hong Kong (ECWW09EG04).