This article describes a cavity ring-down spectrometer (CaRDS) specifically designed and constructed for installation on the NOAA WP-3D Orion (P-3) aircraft for sensitive, rapid in situ measurement of NO3 and N2O5. While similar to our previously described CaRDS instrument, this instrument has significant improvements in the signal-to-noise ratio, the time resolution, and in overall size and weight. Additionally, the instrument utilizes a custom-built, automated filter changer that was designed and constructed to meet the requirement for removal of particulate matter in the airflow while allowing fully autonomous instrument operation. The CaRDS instrument has a laboratory detection sensitivity of 4×10−11cm−1 in absorbance or 0.1pptv (pptv denotes parts per trillion volume) of NO3 in a 1s average, although the typical detection sensitivities encountered in the field were 0.5pptv for NO3 and 1pptv for N2O5. The instrument accuracy is 25% for NO3 and 20%–40% for N2O5, limited mainly by the uncertainty in the inlet transmission. The instrument has been deployed on the P-3 aircraft as part of a major field campaign in the summer of 2004 and during several ground and tower deployments near Boulder, CO.
A new instrument, the Airborne Chromatograph for Atmospheric Trace Species IV (ACATS‐IV), for measuring long‐lived species in the upper troposphere and lower stratosphere is described. Using an advanced approach to gas chromatography and electron capture detection, the instrument can detect low levels of CFC‐11 (CCl3F), CFC‐12 (CCl2F2), CFC‐113 (CCl2F‐CClF2), methyl chloroform (CH3CCl3), carbon tetrachloride (CCl4), nitrous oxide (N2O), sulfur hexafluoride (SF6), Halon‐1211 (CBrClF2), hydrogen (H2), and methane (CH4) acquired in ambient samples every 180 or 360 s. The instrument operates fully‐automated onboard the NASA ER‐2 high‐altitude aircraft on flights lasting up to 8 hours or more in duration. Recent measurements include 24 successful flights covering a broad latitude range (70°S–61°N) during the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA) campaign in 1994.
Abstract. We report the application of cavity ring-down spectroscopy (CARDS), a high-sensitivity absorption technique, to the in-situ detection of both NO3 and N205 in ambient air.The detection limit for NO3, measuring absorption in its strong, 662-nm band, is 0.
This paper describes the design and application of a pulsed cavity ring-down aerosol extinction spectrometer (CRD-AES) for insitu atmospheric measurement of the aerosol extinction coefficient and its relative humidity dependence. This CRD-AES measures the aerosol extinction coefficient (σ ep ) at 355 nm, 532 nm, 683 nm, and 1064 nm with a minimal size dependent bias for particles with diameter less than 10 μm. The σ ep at 532 nm is measured with an accuracy of 1% when extinction is ≥10 Mm −1 . The precision is limited by statistical fluctuations within the small optical volume and the time resolution of extinction at 2% uncertainty for various air mass types is evaluated. The CRD-AES is configured with two separate cavity ring-down cells for measurement of the extinction coefficient at 532 nm. This allows the determination of the RH dependence of extinction at 532 nm through independent RH control of the sample for each measurement. Gas phase absorption and minimization of potential interferences is also considered.
This article describes the application of cavity ring-down spectroscopy (CaRDS) to the simultaneous concentration measurement of nitrate radical, NO3, and dinitrogen pentoxide, N2O5, in the ambient atmosphere. The sensitivity for detection of both NO3 and N2O5 is 0.5 pptv (2σ) for a 5 s integration, comparable to or better than previous measurements of NO3 (e.g., via DOAS), but with significantly better time resolution. Furthermore, direct measurement of N2O5 represent a previously unavailable capability. Concentrations of both species are measured simultaneously in two separate flow systems and optical cavities pumped by the same pulsed dye laser at 662 nm. One of the flow systems remains at ambient temperature for detection of NO3, while the other is heated to 80 °C to induce thermal decomposition of N2O5 providing a measurement of the sum of the NO3 and N2O5 concentrations. This article outlines a series of laboratory and field tests of the instrument’s performance. Important considerations include signal acquisition, zero measurements, aerosol interference, flow system losses, and the conversion efficiency for N2O5 thermolysis to NO3. We describe the limitations of this method and show how they can be quantified and accounted for in field measurements.
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