Development of a new Long Path Absorption Photometer (LOPAP) instrument for the sensitive detection of NO 2 in the atmosphere

Abstract

A compact and simple instrument for the sensitive detection of NO 2 in the atmosphere has been developed. NO 2 is sampled in a stripping coil by a selective chemical reaction, converted into a highly absorbing dye, which is detected by long path absorption in a liquid core waveguide. Several interferences were quantified in the laboratory which so far can all be neglected. The significant interferences against HONO and O 3 were suppressed by using an upstream HONO/O 3-scrubber. The instrument has a detection limit of 2 pptv, an accuracy of 10 % and a precision of 0.5 % for 3 min time resolution. Thus, the new NO 2-LOPAP technique is more sensitive than known commercial NO 2 instruments. The new analyzer is much simpler to apply than other highly sensitive and selective NO 2 methods, e.g. LIF or REMPI methods. The new instrument allows an absolute calibration that can be easily performed with liquid nitrite standards, which is a significant advantage compared with other NO 2 measurement techniques for which NO 2 calibration gas mixtures are typically necessary. The new instrument has been validated against the chemiluminescence technique during an urban field campaign and against the FTIR technique in a smog chamber under complex photosmog conditions. The data sets exhibit high correlation and excellent agreement. © Author(s) 2011.