ABSTRACT: The detection of atmospheric NO3 radicals is still challenging owing to its low mixing
ratios (�1 to 300 pptv) in the troposphere. While long-path differential optical absorption
spectroscopy (DOAS) is a well established NO3 detection approach for over 25 yr,
5 newly sensitive techniques have been developed in the past decade. This publication
outlines the results of the first comprehensive intercomparison of seven instruments
developed for the spectroscopic detection of tropospheric NO3. Four instruments were
based on cavity ring-down spectroscopy (CRDS), two utilised open-path cavity enhanced
absorption spectroscopy (CEAS), and one applied “classical” long-path DOAS.
10 The intercomparison campaign “NO3Comp” was held at the atmosphere simulation
chamber SAPHIR in J¨ ulich (Germany) in June 2007. Twelve experiments were performed
in the well mixed chamber for variable concentrations of NO3, N2O5, NO2, hydrocarbons,
and water vapour, in the absence and in the presence of inorganic or
organic aerosol. The overall precision of the cavity instruments varied between 0.5 and
15 5 pptv for integration times of 1 s to 5min; that of the DOAS instrument was 9 pptv for an
acquisition time of 1 min. The NO3 data of all instruments correlated excellently with the
NOAA-CRDS instrument, which was selected as the common reference because of its
superb sensitivity, high time resolution, and most comprehensive data coverage. The
median of the coefficient of determination (r2) over all experiments of the campaign (60
20 correlations) is r2 =0.981 (25th/75th percentiles: 0.949/0.994; min/max: 0.540/0.999).
The linear regression analysis of the campaign data set yielded very small intercepts
(1.2±5.3 pptv) and the average slope of the regression lines was close to unity (1.02,
min: 0.72, max: 1.36). The deviation of individual regression slopes from unity was
always within the combined accuracies of each instrument pair. The very good cor-
respondence between the NO3 measurements by all instruments for aerosol-free experiments
indicates that the losses of NO3 in the inlet of the instruments were determined
reliably by the participants for the corresponding conditions. In the presence of
inorganic or organic aerosol, however, differences in the measured NO3 mixing ratios were detectable among the instruments. In individual experiments the discrepancies
increased with time, pointing to additional NO3 radical losses by aerosol deposited
onto the inlet walls of the instruments. Instruments using DOAS analyses showed no
significant effect of aerosol on the detection of NO3. No hint of a cross interference of
NO2 5 was found. The effect of non-Lambert–Beer behaviour of water vapour absorption
lines on the accuracy of the NO3 detection by broadband techniques was small
and well controlled. The NO3Comp campaign demonstrated the high quality, reliability
and robustness of performance of current state-of-the-art instrumentation for NO3
AMTD. 01/2013; 6:303-279.
ABSTRACT: NO2 concentrations were measured by various instruments during the NO3Comp campaign at the atmosphere simulation chamber SAPHIR at Forschungszentrum Julich, Germany, in June 2007. Analytical methods included photolytic conversion with chemiluminescence (PC-CLD), broadband cavity ring-down spectroscopy (BBCRDS), pulsed cavity ring-down spectroscopy (CRDS), incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS), and laser-induced fluorescence (LIF). All broadband absorption spectrometers were optimized for the detection of the main target species of the campaign, NO3, but were also capable of detecting NO2 simultaneously with reduced sensitivity. NO2 mixing ratios in the chamber were within a range characteristic of polluted, urban conditions, with a maximum mixing ratio of approximately 75 ppbv. The overall agreement between measurements of all instruments was excellent. Linear fits of the combined data sets resulted in slopes that differ from unity only within the stated uncertainty of each instrument. Possible interferences from species such as water vapor and ozone were negligible under the experimental conditions.
Atmospheric Measurement Techniques 01/2010; 3:21-37. · 3.34 Impact Factor
ABSTRACT: Iodine emissions from the dominant six macroalgal species in the coastal regions around Roscoff, France, have been modelled to support the Reactive Halogens in the Marine Boundary Layer Experiment (RHaMBLe) undertaken in September 2006. A two-dimensional model is used to explore the relationship between geographically resolved regional emissions (based on maps of seaweed beds in the area and seaweed I2 emission rates previously measured in the laboratory) and in situ point and line measurements of I2 performed respectively by a broadband cavity ringdown spectroscopy (BBCRDS) instrument sited on the shoreline and a long-path differential optical absorption spectroscopy (LP-DOAS) instrument sampling over an extended light path to an off-shore island. The modelled point and line I2 concentrations compare quantitatively with BBCRDS and LP-DOAS measurements, and provide a link between emission fields and the different measurement geometries used to quantify atmospheric I2 concentrations during RHaMBLe. Total I2 emissions over the 100 km2 region around Roscoff are calculated to be 1.7×1019 molecules per second during the lowest tides. During the night, the model replicates I2 concentrations up to 50 pptv measured along the LP-DOAS instrument's line of sight, and predicts spikes of several hundred pptv in certain conditions. Point I2 concentrations up to 50 pptv are also calculated at the measurement site, in broad agreement with the BBCRDS observations. Daytime measured concentrations of I2 at the site correlate with modelled production and transport processes. However substantial recycling of the photodissociated I2 is required for the model to quantitatively match measured concentrations. This result corroborates previous modelling of iodine and NOx chemistry in the semi-polluted marine boundary layer which proposed a mechanism for recycling I2 via the formation, transport and subsequent reactions of the IONO2 reservoir compound. The methodology presented in this paper provides a tool for linking spatially distinct measurements to inhomogeneous and temporally varying emission fields.
Atmospheric Chemistry and Physics. 01/2010;
ABSTRACT: NO<sub>2</sub> concentrations were measured by various instruments during the NO3Comp campaign at the atmosphere simulation chamber SAPHIR at Forschungszentrum Jülich, Germany, in June 2007. Analytical methods included photolytic conversion with chemiluminescence (PC-CLD), broadband cavity ring-down spectroscopy (BBCRDS), pulsed cavity ring-down spectroscopy (CRDS), incoherent broadband cavity-enhanced absorption spectroscopy (IBB-CEAS), and laser-induced fluorescence (LIF). All broadband absorption spectrometers were optimized for the detection of the main target species of the campaign, NO<sub>3</sub>, but were also capable of detecting NO<sub>2</sub> simultaneously with reduced sensitivity. NO<sub>2</sub> mixing ratios in the chamber were within a range characteristic of polluted, urban conditions, with a maximum mixing ratio of approximately 75 ppbv. The overall agreement between measurements of all instruments was excellent. Linear fits of the combined data sets resulted in slopes that differ from unity only within the stated uncertainty of each instrument. Possible interferences from species such as water vapor and ozone were negligible under the experimental conditions.
Atmospheric Measurement Techniques. 01/2010;
ABSTRACT: The absorption of solar radiation by water dimer molecules in the Earth's atmosphere can potentially act as a positive feedback effect for climate change. There seems little doubt from the results of previous laboratory and theoretical studies that significant concentrations of the water dimer should be present in the atmosphere, yet attempts to detect water dimer absorption signatures in atmospheric field studies have so far yielded inconclusive results. Here we report spectral measurements in the near-infrared in the expected region of the third overtone of the water dimer hydrogen-bonded OHb stretching vibration around 750 nm. The results were obtained using broadband cavity ringdown spectroscopy (BBCRDS), a methodology that allows absorption measurements to be made under controlled laboratory conditions but over absorption path lengths representative of atmospheric conditions. In order to account correctly and completely for overlapping absorption of monomer molecules in the same spectral region, we have also constructed a new list of spectral data (UCL08) for the water monomer in the 750–20 000 cm−1 (13 μm–500 nm) range. Our results show that the additional lines included in the UCL08 spectral database provide a substantially improved representation of the measured water monomer absorption in the 750 nm region, particularly at wavelengths dominated by weak monomer absorption features. No absorption features which could not be attributed to the water monomer were detected in the BBCRDS experiments up to water mixing ratios more than an order of magnitude greater than those in the ambient atmosphere. The absence of detectable water dimer features leads us to conclude that, in the absence of significant errors in calculated dimer oscillator strengths or monomer/dimer equilibrium constants, the widths of water dimer features present around 750 nm must be substantially greater (~100 cm−1 HWHM) than those reported at longer wavelengths.
Atmospheric Chemistry and Physics Discussions. 01/2010;
ABSTRACT: This paper presents a summary of the measurements that were made during the heavily-instrumented Reactive Halogens in the Marine Boundary Layer (RHaMBLe) coastal study in Roscoff on the North West coast of France. It was clearly demonstrated that iodine-mediated coastal particle formation occurs, driven by daytime low tide emission of molecular iodine, I2, by macroalgal species fully or partially exposed by the receding waterline. Ultrafine particle concentrations strongly correlate with the rapidly recycled reactive iodine species, IO, produced at high concentrations following photolysis of I2. The heterogeneous macroalgal I2 sources lead to variable relative concentrations of iodine species observed by path-integrated and in situ measurement techniques. Apparent particle emission fluxes were associated with an enhanced apparent depositional flux of ozone, consistent with both a direct O3 deposition to macroalgae and involvement of O3 in iodine photochemistry and subsequent particle formation below the measurement height. The magnitude of the particle formation events was observed to be greatest at the lowest tides with higher concentrations of ultrafine particles growing to much larger sizes, probably by the condensation of anthropogenically-formed condensable material. At such sizes the particles should be able to act as cloud condensation nuclei at reasonable atmospheric supersaturations.
Atmospheric Chemistry and Physics Discussions. 01/2009;
ABSTRACT: Emissions from the dominant six macroalgal species in the coastal regions around Rosccoff, France, have been modelled to support the Reactive Halogens in the Marine Boundary Layer Experiment (RHaMBLE) campaign undertaken in September 2006. A 2-D model was used to explore the relationship between point and line measurements of molecular iodine concentrations, and total regional emissions, based on seaweed I2 emission rates measured in the laboratory. The relatively simple modelling technique has produced modelled point and line data, which compare quantitatively with campaign measurements, and provide a link between emission fields and the different measurement geometries used to quantify atmospheric I2 concentrations during RHaMBLE. During nightime, absolute concentrations in the region of 5 pptv are predicted and measured in the LP-DOAS measurements, with site concentrations predicted and measured up to 40 pptv, compatible with concentrations above Laminariales beds of approximately 2.5 ppbv. Daytime measured concentrations of I2 at site correlate with modelled production and transport processes, however complete recycling of photodissociated I2 is required in the model to quantitatively match measured concentrations. Additional local source terms are suggested to provide a feasible mechanism to account for this discrepancy.Total of I2 emissions over the 100 km2 region around Roscoff are calculated as 1.5×1019 molecules per second during the lowest tides.
Atmospheric Chemistry and Physics Discussions. 01/2009;
ABSTRACT: A fast Fourier transform (FFT) method for analysis of ring-down decays from a cavity ring-down (CRD) spectrometer has been tested and compared with alternative fitting methods. The ring-down times derived from the FFT method are obtained with a precision close to that of the Levenberg–Marquardt non-linear least-squares method, but the fitting algorithm is ~100 times faster, allowing real-time fitting of individual ring-down traces on a personal computer. Advantages of the FFT method are discussed, and the method is demonstrated for the measurement of NO2 partial pressures equivalent to mixing ratios of 150 pptv and above in laboratory air, using a CRD spectrometer based on an external cavity diode laser operating at wavelengths around 410 nm. The absorption by NO2 is distinguished from other cavity losses either by using synthetic (zero) air reference samples, or by diverting the sampled laboratory airflow through an NO2 chemical scrubber consisting of hydroxyapatite on a TiO2 substrate. Typical mixing ratios of NO2 in the laboratory air are ~25 ppbv.
Applied Physics B 06/2005; 81(1):135-141. · 2.19 Impact Factor