Sequential multiple analyses of atmospheric nitrous acid and nitrogen oxides

Area of Science:

• Environmental Chemistry
• Analytical Chemistry

Background:

• Nitrogen-oxygen compounds like HONO, NO2, and NO are crucial in atmospheric chemistry, influencing pollution and OH radical formation.
• Simultaneous measurement of these interconvertible gases is vital for understanding atmospheric processes.

Purpose of the Study:

• To develop and validate a Sequential Injection Analysis (SIA) method for simultaneous multi-gas monitoring of atmospheric HONO, NO2, and NO.
• To demonstrate the efficacy of SIA as a tool for atmospheric analysis.

Main Methods:

• Atmospheric gases were collected in diffusion scrubbers containing HCl or triethanolamine solution, converting analytes to nitrite ions.
• Nitrite samples were analyzed using SIA, involving reagent addition (C-acid), a heated reaction, alkalinization, and detection via a homemade fluorescence detector.
• The SIA system utilized a 12-port selection valve and a 2.5-ml syringe for sample and reagent handling.

Main Results:

• The SIA method successfully monitored atmospheric HONO, NO2, and NO at rates of 3-4 times per hour.
• Limits of detection were determined to be 0.22 ppbv for HONO, 0.28 ppbv for NO2, and 0.35 ppbv for NO.
• Data from SIA for NO2 and NO showed good agreement when compared to a chemiluminescence instrument.

Conclusions:

• Sequential Injection Analysis (SIA) is a viable and effective tool for multi-gas atmospheric monitoring.
• The developed method allows for the simultaneous measurement of HONO, NO2, and NO using a single analytical system.
• Observed increases in HONO levels towards the end of rain periods warrant further investigation into atmospheric chemical dynamics.