Here, we present a new automated instrument for semicontinuous gradient measurements of water-soluble reactive trace gas species (NH3, HNO3, HONO, HCl, and SO2) and their related aerosol compounds (NH4+, NO3-, Cl-, SO4(2-)). Gas and aerosol samples are collected simultaneously at two heights using rotating wet-annular denuders and steam-jet aerosol collectors, respectively. Online (real-time) analysis using ion chromatography (IC) for anions and flow injection analysis (FIA) for NH4+ and NH3 provide a half-hourly averaged gas and aerosol gradients within each hour. Through the use of syringe pumps, IC preconcentration columns, and high-quality purified water, the system achieves detection limits (3sigma-definition) under field conditions of typically: 136/207,135/114, 29/ 22,119/92, and 189/159 ng m(-3) for NH3/NH4+, HNO3/NO3-, HONO/ NO2-, HCl/Cl- and SO2/SO4(2-), respectively. The instrument demonstrates very good linearity and accuracy for liquid and selected gas phase calibrations over typical ambient concentration ranges. As shown by examples from field experiments, the instrument provides sufficient precision (3-9%), even at low ambient concentrations, to resolve vertical gradients and calculate surface-atmosphere exchange fluxes undertypical meteorological conditions of the atmospheric surface layer using the aerodynamic gradient technique.

Abstract. An intercomparison of different radiometric techniques measuring atmospheric photolysis frequencies j(NO2), j(HCHO) and j(O1D) was carried out in a two-week field campaign in June 2005 at Jülich, Germany. Three double-monochromator based spectroradiometers (DM-SR), three single-monochromator based spectroradiometers with diode-array detectors (SM-SR) and seventeen filter radiometers (FR) (ten j(NO2)-FR, seven j(O1D)-FR) took part in this comparison. For j(NO2), all spectroradiometer results agreed within ±3%. For j(HCHO), agreement was slightly poorer between −8% and +4% of the DM-SR reference result. For the SM-SR deviations were explained by poorer spectral resolutions and lower accuracies caused by decreased sensitivities of the photodiode arrays in a wavelength range below 350 nm. For j(O1D), the results were more complex within +8% and −4% with increasing deviations towards larger solar zenith angles for the SM-SR. The direction and the magnitude of the deviations were dependent on the technique of background determination. All j(NO2)-FR showed good linearity with single calibration factors being sufficient to convert from output voltages to j(NO2). Measurements were feasible until sunset and comparison with previous calibrations showed good long-term stability. For the j(O1D)-FR, conversion from output voltages to j(O1D) needed calibration factors and correction functions considering the influences of total ozone column and elevation of the sun. All instruments showed good linearity at photolysis frequencies exceeding about 10% of maximum values. At larger solar zenith angles, the agreement was non-uniform with deviations explainable by insufficient correction functions. Comparison with previous calibrations for some j(O1D)-FR indicated drifts of calibration factors.

Abstract. Nitrogen dioxide (NO2) plays an important role in atmospheric pollution, in particular for tropospheric ozone production. However, the removal processes involved in NO2 deposition to terrestrial ecosystems are still the subject of ongoing discussion. This study reports NO2 flux measurements made over a meadow using the eddy covariance method. The measured NO2 deposition fluxes during daytime were about a factor of two lower than a priori calculated fluxes using the Surfatm model without taking into account an internal (also called mesophyllic or sub-stomatal) resistance. Neither an underestimation of the measured NO2 deposition flux due to chemical divergence or an in-canopy NO2 source nor an underestimation of the resistances used to model the NO2 deposition explained the large difference between measured and modelled NO2 fluxes. Thus, only the existence of the internal resistance could account for this large discrepancy between model and measurements. The median internal resistance was estimated to be 300 s m−1 during daytime, but exhibited a large variability (100–800 s m−1). In comparison, the stomatal resistance was only around 100 s m−1 during daytime. Hence, the internal resistance accounted for 50–90% of the total leaf resistance to NO2. This study presents the first clear evidence and quantification of the internal resistance using the eddy covariance method; i.e. plant functioning was not affected by changes of microclimatological (turbulent) conditions that typically occur when using enclosure methods.

Nitrogen dioxide (NO₂) plays an important role in atmospheric pollution, in particular for tropospheric ozone production. However, the removal processes involved in NO₂ deposition to terrestrial ecosystems are still subject of ongoing discussion. This study reports NO₂ flux measurements made over a meadow using the eddy covariance method. The measured NO₂ deposition fluxes during daytime were about a factor of two lower than a priori calculated fluxes using the Surfatm model without taking into account an internal (also called mesophyllic or sub-stomatal) resistance. Neither an underestimation of the measured NO₂ deposition flux due to chemical divergence or direct NO₂ emission, nor an underestimation of the resistances used to model the NO₂ deposition explained the large difference between measured and modelled NO₂ fluxes. Thus, only the existence of the internal resistance could account for this large discrepancy between model and measurements. The median internal resistance was estimated to 300 s m⁻¹ during daytime, but exhibited a large variability (100 s m⁻¹ to 800 s m⁻¹). In comparison, the stomatal resistance was only around 100 s m⁻¹ during daytime. Hence, the internal resistance accounted for 50% to 90% of the total leaf resistance to NO₂. This study presents the first clear evidence and quantification of the internal resistance using the eddy covariance method, i.e. plant functioning was not affected by changes of microclimatological (turbulent) conditions that typically occur when using enclosure methods

Abstract. An intercomparison of different radiometric techniques measuring atmospheric photolysis frequencies j(NO2), j(HCHO) and j(O1D) was carried out in a two-week field campaign in June 2005 at Jülich, Germany. Three double-monochromator based spectroradiometers (DM-SR), three single-monochromator based spectroradiometers with diode-array detectors (SM-SR) and seventeen filter radiometers (FR) (ten j(NO2)-FR, seven j(O1D)-FR) took part in this comparison. For j(NO2), all spectroradiometer results agreed within ±3%. For j(HCHO), agreement was slightly poorer between −8% and +4% of the DM-SR reference result. For the SM-SR deviations were explained by poorer spectral resolutions and lower accuracies caused by decreased sensitivities of the photodiode arrays in a wavelength range below 350 nm. For j(O1D), the results were more complex within +8% and −4% with increasing deviations towards larger solar zenith angles for the SM-SR. The direction and the magnitude of the deviations were dependent on the technique of background determination. All j(NO2)-FR showed good linearity with single calibration factors being sufficient to convert from output voltages to j(NO2). Measurements were feasible until sunset and comparison with previous calibrations showed good long-term stability. For the j(O1D)-FR, conversion from output voltages to j(O1D) needed calibration factors and correction functions considering the influences of total ozone column and altitude of the sun. All instruments showed good linearity at photolysis frequencies exceeding about 10% of maximum values. At larger solar zenith angles, the agreement was non-uniform with deviations explainable by insufficient correction functions. Comparison with previous calibrations for some j(O1D)-FR indicated drifts of calibration factors.

Die Richtlinie VDI 3790 Blatt 3 ist eine wichtige Grundlage für die Abschätzung diffuser Staubemissionen durch Umschlagvorgänge. Vergleicht man die Ergebnisse dieser Berechnungsmethode mit anderen Berechnungsansätzen sowie mit messtechnisch ermittelten Staub- emissionen für den Umschlag mineralischer Rohstoffe in Steinbrüchen, stellt man fest, dass die berechneten diffusen Staubemissionen nach der Methode von VDI 3790 Blatt 3 deutlich höher ausfallen als die Berechnungen mittels anderer Berechnungsansätze. Es wird als notwendig angesehen, die Eingangsparameter der Berechnungsmethode (speziell die „Neigung zum Stauben“ in Kombination mit der Umschlagmenge) besser an Messdaten anzupassen, um damit zukünftig eine zu starke Überschätzung der Emissionen zu vermeiden. Zusätzlich sollten validierte Angaben zur Korngrößenverteilung emittierter Stäube direkt an der Quelle ermittelt und in die Richtlinie aufgenommen werden.

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