We have developed a new system for measuring photochemical ozone production rates in the atmosphere. Specifically, the system measures the net photochemical oxidant (Ox: the sum of ozone (O3) and nitrogen dioxide (NO2)) production rates (P–L(Ox)). Measuring Ox avoids issues from perturbations to the photostationary states between nitrogen oxides (NOx) and O3. This system has “reaction” and “reference” chambers. Ambient air is introduced into both chambers, and Ox 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 Ox concentration is measured as NO2 using a laser-induced fluorescence technique. P–L(Ox) was obtained by dividing the difference in Ox 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(Ox) measurement system was characterized, and the current detection limit of P–L(Ox) was determined to be 0.54 ppbv h–1 with an integration time of 60 s (S/N = 2), assuming an ambient Ox concentration of 100 ppbv. Field measurements of P–L(Ox) were conducted using the system at a remote forest location.

A photolytic converter of nitrogen dioxide (NO2) to nitric oxide (NO) using light-emitting diodes (LEDs) has been designed to measure NO2 in the troposphere. The typical electrical power consumption of the photolytic converter (PLC) is only 44 W. The maximum conversion efficiency of NO2 to NO of the photolytic converter is around 90%, which is higher than that of metal halides or high-pressure Xe arc lamps (up to ∼70%). The conversion efficiency of the PLC was almost constant for at least 2.5 months. The conversion efficiency of peroxyacetyl nitrate by the LED-PLC was measured to be 2.6 ± 0.1% (1σ). The interference of HONO using the PLC was experimentally estimated to be less than 3%, which is within the uncertainty of the instrument. An intercomparison of NO2 measurements between the PLC-CLD and the laser-induced fluorescence (LIF) technique was conducted, and the NO2 concentrations measured by the PLC-CLD method were in agreement with those obtained by the LIF technique, within the uncertainties of the instruments. Continuous observations were made on Fukue Island, a remote area. These results demonstrate the performance of the PLC for continuous ambient measurements.

A particulate nitrate analyzer based on a scrubber difference/NO−O3 chemiluminescence method (SD−CL method) has been developed for measuring nitrate concentrations in remote areas. Particulate nitrate concentrations (NO3−(p)) were analyzed by the difference between the concentrations of NOy − gaseous nitric acid (HNO3) and NOy − HNO3 − NO3−(p). Annular denuders coated with NaCl and PTFE filter were used as the scrubbers for HNO3 and NO3−(p), respectively. The transmission efficiency of coarse particles in the denuder was found to be 93.4 ± 5.8%, so the loss of NO3−(p) to the denuder was within the uncertainty of the particulate nitrate analyzer (±20%). The measurements of NOy, HNO3, and NO3−(p) were conducted from March 15 to April 31, 2008, at Cape Hedo, Okinawa, Japan. Over 99.5% of the observed concentrations of NO3−(p) for 10 min integration times were higher than the detection limit of the SD−CL method (0.18 μg m−3). The least-squares fit of the R&P nitrate monitor against the SD−CL method yielded a slope of 0.67 ± 0.02 and a correlation coefficient of R = 0.73. This result indicates that this method could also measure NO3−(p) when the diameter of aerosols was larger than 10 μm. The SD−CL method was found to be useful as a measurement system for NO3−(p) in remote areas where coarse NO3−(p) dominates.

A proton transfer reaction-time-of-flight mass spectrometer (PTR-TOFMS) has been developed for real-time measurements of volatile organic compounds in air. The instrument is designed to be operated with a hollow cathode discharge ion source and an ion drift tube at relatively high pressures. Each component of the system, an ion source, a drift tube, an ion transfer region, and a time-of-flight mass spectrometer, are in detail characterized by a number of laboratory experiments. The optimized instrumental configuration enables us to gain high intensities of hydronium (H3O+) ions, typically ∼7 × 105 counts for 1-min integration at a drift tube pressure of ∼5 Torr. It also suppresses background signals, and interferences from sample air (NO+ and O2+), which undergo fast reactions with volatile organic compounds, to ∼0.5% of those of H3O+ ions. We find that the use of the custom-built discharge source show higher overall sensitivities than of a commercially available radioactive source. Potentials to detect oxygenated VOCs (aldehydes, ketones, and alcohols), halocarbons, and amines are also suggested. The detection limits for acetaldehyde, acetone, isoprene, benzene, toluene, and p-xylene were determined to be at the sub-ppbv levels for a 1-min integration time. A good linear response at trace levels is certified, but slight sensitivity dependency on water vapor contents is revealed. We finally demonstrate that the instrument can be used for on-line monitoring to detect large variations from emission sources in real-time.