Measurement of HONO in gas.

Description of the instrument:

The LOPAP works continuously in situ to measure nitrous acid (HONO) in the gas phase with wet chemical sampling and photometric detection.Nitrous acid is of great importance for atmospheric analysis, as its photolysis leads to the formation of OH radicals. In addition, this substance is an indoor air pollutant, which is also carcinogenic. The LOPAP can be used to measure the ambient air, to monitor the indoor air and to control the exhaust air in gas measuring devices. The concentration range extends from a few ppt to a few ppm. Due to the two-channel concept of the measuring instrument, interferences can be neglected in relation to other available HONO measuring techniques. This instrument can also be used to measure low nitrite concentrations in aqueous samples (approx. 10-9 M).



  • High sensitivity: detection limit 1-2 ppt
  • High application range: Measuring range 5 ppt- 2 ppm
  • Time resolution: 1-5 min. (depending on the measuring range)
  • Accuracy: approx. 10 % ± 2 ppt
  • Precision: approx. 1 %
  • Interferences can be neglected: tested for NO2, NO2+O3, NO2+SO2, NO2+hydrocarbonates, NO2+diesel exhaust gases, NO, HNO3, HNO3+HCHO, O3, PAN, alkyl nitrates
  • Simple calibration: with liquid nitrite standard
  • Compact design: 19 inch instrument
  • Data output: (DAQ-700 A/D) Interface to a PC (notebook)
  • Power connection: 24 V DC or 230 V AC


Published literature:

nature Vol 440/9 March 2006 Page 195-198
“Photosensitized reduction of nitrogen dioxide on humic acid as a source of nitrous acid”

Geophysical Research Letters, Vol. 32, L05818,
doi: 10.1029/2005GL022524, 2005
“Daytime formation of nitrous acid: A major source of OH radicals in a forest”

In cooperation with:

Prof. Dr. Peter Wiesen /PD Dr. Joerg Kleffmann;
Physical Chemistry/FB C
University of Wuppertal
Gauss Street 20
D-42097 Wuppertal
PHONE: +49 202 439 2515
FAX: +49 202 439 2505 or 2757
Email: wiesen@uni-wuppertal.de