Direct measurement system of nitrogen dioxide in the atmosphere using a blue light-emitting diode induced fluorescence technique

Validation of in situ Measurements of Atmospheric Nitrous Acid Using Incoherent Broadband Cavity-enhanced Absorption Spectroscopy

Incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) is a useful technique for measuring trace gaseous species in the atmosphere. Recently, IBBCEAS was used to measure concentrations of nitrous acid (HONO) in the troposphere to resolve controversies related to its formation and loss. Here, measurements of HONO and a mixture of HONO and NO₂ using IBBCEAS were validated by comparing them with those obtained with a NOx analyzer. Good agreement was found between these methods, given their respective experimental uncertainties. The detection limit of our IBBCEAS instrument was 0.2 ppbv, with a signal-to-noise ratio of 1, and a 5-min integration time.

New System for Measuring the Photochemical Ozone Production Rate in the Atmosphere

We have developed a new system for measuring photochemical ozone production rates in the atmosphere. Specifically, the system measures the net photochemical oxidant (O_x: the sum of ozone (O₃) and nitrogen dioxide (NO₂)) production rates (P-L(O_x)). Measuring O_x avoids issues from perturbations to the photostationary states between nitrogen oxides (NO_x) and O₃. This system has "reaction" and "reference" chambers. Ambient air is introduced into both chambers, and O_x is photochemically produced in the reaction chamber and not generated in the reference chamber. Air from the chambers is alternately introduced into an NO-reaction (NO: nitric oxide) tube to convert O₃ to NO₂, and then the O_x concentration is measured as NO₂ using a laser-induced fluorescence technique. P-L(O_x) was obtained by dividing the difference in O_x concentrations between air samples from the two chambers by the mean residence time of the air in the reaction chamber. In this study, the P-L(O_x) measurement system was characterized, and the current detection limit of P-L(O_x) was determined to be 0.54 ppbv h^-1 with an integration time of 60 s (S/N = 2), assuming an ambient O_x concentration of 100 ppbv. Field measurements of P-L(O_x) were conducted using the system at a remote forest location.

Analytical devices based on light-emitting diodes--a review of the state-of-the-art

A general overview of the development of the uses of light-emitting diodes in analytical instrumentation is given. Fundamental aspects of light-emitting diodes, as far as relevant for this usage, are covered in the first part. The measurement of light intensity is also discussed, as this is an essential part of any device based on light-emitting diodes as well. In the second part, applications are discussed, which cover liquid and gas-phase absorbance measurements, flow-through detectors for chromatography and capillary electrophoresis, sensors, as well as some less often reported methods such as photoacoustic spectroscopy.