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A new, two-channel instrument for simultaneous NO3 and N2O5 monitoring was used to make the first comprehensive set of nocturnal NOx measurements (NO, NO2, NO3 and N2O5) at the Taunus Observatory, a rural mountain site (Kleiner Feldberg) in South-western Germany. In May 2008, NO3 and N2O5 mixing ratios were well above the instrumental detection limit (a few ppt) on all nights of the campaign and were characterised by large variability resulting from inhomogeneously distributed sinks. The concentrations of NO3, N2O5 and NO2 were consistent with the equilibrium constant, K2, defining the rates of formation and thermal dissociation of N2O5. A steady-state lifetime analysis showed that nocturnal NOx losses were generally dominated by reaction of NO3 with volatile organic compounds in this forested region, with N2O5 uptake to aerosols of secondary importance. Analysis of a limited dataset obtained at high relative humidity indicated that the loss of N2O5 by reaction with water vapour is less efficient (> factor 3) than derived using laboratory kinetic data. The fraction of NOx present as NO3 and N2O5 reached ≈20% on some nights, with night-time losses of NOx competing with daytime losses.
A new, two-channel instrument for simultaneous NO3 and N2O5 monitoring was used to make the first comprehensive set of nocturnal NOx measurements (NO, NO2, NO3 and N2O5) at the Taunus Observatory, a rural mountain site (Kleiner Feldberg) in South-western Germany. In May 2008, NO3 and N2O5 mixing ratios were well above the instrumental detection limit (a few ppt) on all nights of the campaign and were characterised by large variability. The concentrations of NO3, N2O5 and NO2 were consistent with the equilibrium constant, K2, defining the rates of formation and thermal dissociation of N2O5. A steady-state lifetime analysis is consistent with the loss of nocturnal NOx being dominated by the reaction of NO3 with volatile organic compounds in this forested region, with N2O5 uptake to aerosols of secondary importance. Analysis of a limited dataset obtained at high relative humidity indicated that the loss of N2O5 by reaction with water vapour is less efficient (>factor 3) than derived using laboratory kinetic data. The fraction of NOx present as NO3 and N2O5 reached ~20% on some nights, with night-time losses of NOx competing with daytime losses.
This paper investigates the potential impact of secondary information on rainfall mapping applying Ordinary Kriging. Secondary information tested is a natural area indicator, which is a combination of topographic features and weather conditions. Cross validation shows that secondary information only marginally improves the final mapping, indicating that a one-day accumulation time is possibly too short.
In this paper we present evidence that the observed increase in tropical upwelling after the year 2000 may be attributed to a change in the Brewer-Dobson circulation pattern. For this purpose, we use the concept of transit times derived from residual circulation trajectories and different in-situ measurements of ozone and nitrous dioxide. Observations from the Canadian midlatitude ozone profile record, probability density functions of in-situ N2O observations and a shift of the N2O-O3 correlation slopes, taken together, indicate that the increased upwelling in the tropics after the year 2000 appears to have triggered an intensification of tracer transport from the tropics into the extratropics in the lower stratosphere below about 500 K. This finding is corroborated by the fact that transit times along the shallow branch of the residual circulation into the LMS have decreased for the same time period (1993–2003). On a longer time scale (1979–2009), the transit time of the shallow residual circulation branch show a steady decrease of about −1 month/decade over the last 30 years, while the transit times of the deep branch remain unchanged. This highlights the fact that a change in the upwelling across the tropical tropopause is not a direct indicator for changes of the whole Brewer-Dobson circulation.
Within the present study the occurrence and fate of the organophosphorus flame retardants and plasticizers tris(2-chloroethyl) phosphate (TCEP), tris(2-chloro-1-methylethyl) phosphate (TCPP), tris(1,3-dichloro-2-propyl) phosphate (TDCP), tris(2-butoxyethyl) phosphate (TBEP), tri-iso-butyl phosphate (TiBP), and tri-n-butyl phosphate (TnBP) in precipitation, lake water, surface runoff and groundwater from urban and remote areas in Germany was investigated between June 2007 and October 2009. 255 samples of precipitation, 210 samples of lentic surface water and 72 samples of groundwater were analyzed for the six organophosphates (OPs) by solid phase extraction followed by gas chromatography-mass spectrometry. The research focused on aspects concerning (1) the atmospheric washout of OPs by precipitation, (2) the temporal variation of OP concentrations in precipitation and in lentic surface waters as well as (3) the pollution of groundwater by OPs. The results of the study emphasize the importance of precipitation as an all-season entry-pathway for OPs in the aquatic environment, particularly in densely populated urban environments with high traffic volume and abundant usage of flame-protected products. No seasonal trends were observed for all analytes in precipitation at the urban sampling site. TCPP dominated in all precipitation and storm water holding tank (SWHT) water samples with maximum levels exceeding 1 µg/L. An accumulation of OPs deposited in SWHTs was observed with concentrations often exceeding those observed in wet precipitation. Median concentrations of TCPP (880 ng/L), TDCP (13 ng/L), and TBEP (77 ng/L) at the urban SWHT were more than twice as high as those measured at the urban precipitation sampling site (403 ng/L, 5 ng/L, 21 ng/L) located close to the SWHT. OP levels in more remote lakes were often below or close to the limits of quantitation (LOQ). Nevertheless, TCPP was the substance with the highest median concentration in rural volcanic lakes (7–18 ng/L) indicating an atmospheric transport of the compound. At urban lakes the median OP concentrations were in the range of 23–61 ng/L (TCEP), 85–126 ng/L (TCPP), <LOQ–53 ng/L (TBEP), 8–10 ng/L (TiBP), and 17–32 ng/L (TnBP). In laboratory experiments, TBEP, TiBP, and TnBP were photochemically degraded in spiked lake water samples upon exposure to sunlight. In the SWHT a seasonal trend with decreasing concentrations in summer/autumn was evident for TiBP and TnBP but not for the chlorinated OPs. The decreasing concentrations can be explained by in-lake photodegradation. Results have also shown that the occurrence of OPs in groundwater is depending on the anthropogenic impact during groundwater recharge/natural replenishment. Infiltration of precipitation was found to be no important entry-pathway for OPs into aquifers at rural sites. Highest OP concentrations (>0.1 µg/L) were determined in groundwater polluted by percolating leachate from contaminated sites or groundwater recharged via bank filtration of OP-loaded recipients. Concentrations of TCEP, TCPP, TiBP and TnBP in groundwater decreased rapidly (89–97%) during bank filtration with increasing distance from the recipient due to adsorption processes and/or biotransformation. Although TCEP and TCPP are stable within the aquifer, they are not suitable as conservative organic tracers in groundwater.