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The Comparisons of Real-time Ammonia Adsorption Measurement in Varying Inlet Tubes and the Different Ammonia Measurement Methods in the Atmosphere 

ABSTRACT
Ammonia (NH3) is an important, albeit sticky, precursor for producing secondary inorganic aerosols (SIA), especially in the form 

of ammonium nitrate (NH4NO3) and ammonium sulfate ((NH4)2SO4). To reduce SIAs, many researchers have attempted to

measure the concentration of ambient NH3 using real-time or passive methods. However, NH3 is a highly sticky gas and is

therefore difficult to measure using real-time methods without incurring losses during measurement. In this study, four different

tubing materials, semi seamless tubes, perfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF),

were used to ascertain the adsorption of NH3 in inlets using real-time instruments. Without heating sample tubes and at 0%

relative humidity (RH), this study shows that PTFE had the least adsorption (i.e., 0% at 1 and 2 m of sample tube), and semi-

seamless tubes had the highest adsorption (i.e., 27.5% at 1 m of sample tube). To calculate the adsorption of NH3 under ambient

conditions, at various inlet lengths, the RH of NH3 was varied from 20% to 80%, which showed that shorter inlets and higher RH

lower NH3 adsorption at inlets (i.e., 1.74 ppb m-1 at 80% RH and 7.48 ppb m-1 at 20% RH). Additionally, inlet heating was

effective in reducing the adsorption of NH3 as the RH decreased. Applying the inlet system (i.e., 2 m of PTFE tube with heating)

showed excellent correlation (slope: 0.995 and coefficient: 0.992) between two different real-time measurements while measuring

ambient air. 

KEY WORDS

Ammonia, Inlet adsorption, Polytetrafluoroethylene, Protocol, Ammonia measurement