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The Hg0 time series recorded at the Mauna Loa Observatory (MLO) in Hawaii between 2002 and 2009 has been analyzed using Empirical Mode Decomposition. This technique has been used in numerous contexts in order to identify periodical variations in time series data. The periodicities observed in the tropical Pacific sea surface temperature (SST), through the data collected from five buoys, are also observed in Hg0 concentrations and the relative humidity measured at the MLO. The lag times in the observed periodicities are related to the position of the buoys with respect to the measurement site. This demonstrates a direct link between climatological phenomena, in this case SST, and measured Hg0 and reflects the influence of ocean SST on Hg0 evasion. This is the first long-term experimental evidence of such a direct effect on Hg0 evasion from the oceanic surface driven by temperature.

Number size distribution of ambient submicron and ultrafine aerosol particles have been measured on a continuous basis (every 10 minutes) for three quarters of the year 1996, at a forest site in Southern Finland. Continuous monitoring offers additional insight over the diurnal dynamics of the submicron size distribution, including existence of clearly separate size modes as well as events of new particle formation. Selected examples of the measured size distributions are presented, including the particle formation events observed at the measurement site. Typical characteristics of days with particle formation events versus days of no events are discussed.

In situ OH measurements were made as part of the spring and summer intensives of Mauna Loa Observatory Photochemistry Experiment (MLOPEX 2). These measurements provided an opportunity to compare measured OH concentrations with those predicted by steady state models which use the many other measurements which made up MLOPEX 2 as input parameters. These models thus provide a highly specific real-time view of the environment in which OH was being measured. Both short- and long-term variations of OH are discussed along with their relation to changes in sources and sinks. In general, agreement between measured and modeled OH concentrations is good during periods when free tropospheric air masses, typically downslope, were present. During periods when certain types of upslope boundary layer air dominated the measurement site, however, measured OH concentration averaged about a factor of 2 lower than the model predictions. Possible reasons for the latter differences are suggested, such as unidentified sinks in the boundary layer air.

[1] Recent studies have shown that measured OH under NOx-limited, high-isoprene conditions are many times higher than modeled OH. In this study, a detailed analysis of the HOx radical budgets under low-NOx, rural conditions was performed employing a box model based on the Master Chemical Mechanism (MCMv3.2). The model results were compared with HOx radical measurements performed during the international HOxComp campaign carried out in Julich, Germany, during summer 2005. Two different air masses influenced the measurement site denoted as high-NOx (NO, 1–3 ppbv) and low-NOx (NO, < 1 ppbv) periods. Both modeled OH and HO2 diurnal profiles lay within the measurement range of all HOx measurement techniques, with correlation slopes between measured and modeled OH and HO2 around unity. Recently discovered interference in HO2 measurements caused by RO2 cross sensitivity was found to cause a 30% increase in measured HO2 during daytime on average. After correction of the measured HO2 data, the model HO2 is still in good agreement with the observations at high NOx but overpredicts HO2 by a factor of 1.3 to 1.8 at low NOx. In addition, for two different set of measurements, a missing OH source of 3.6 ± 1.6 and 4.9 ± 2.2 ppb h−1 was estimated from the experimental OH budget during the low-NOx period using the corrected HO2 data. The measured diurnal profile of the HO2/OH ratio, calculated using the corrected HO2, is well reproduced by the MCM at high NOx but is significantly overestimated at low NOx. Thus, the cycling between OH and HO2 is better described by the model at high NOx than at low NOx. Therefore, similar comprehensive field measurements accompanied by model studies are urgently needed to investigate HOx recycling under low-NOx conditions.

[1] The International Special Committee on Radio Interference (CISPR) (CISPR 16-1-4) measured the site voltage standing wave ratio (SVSWR) to determine the site imperfections of a radiated emission measurement site above 1 GHz. However, the technical background of the SVSWR measurement parameters is not included in this standard. In this paper, we first propose a simple propagation model to evaluate the relation between the SVSWR parameters and the measurement values. The calculated SVSWR values of the total displacement defined in CISPR 16-1-4 (0.4 m) were almost the same as those obtained when the transmitting antenna was moved up to 2.0 m from the reference point. In addition, the SVSWR values obtained with a 50 MHz frequency resolution, as defined in CISPR 16-1-4 were almost the same as those values obtained with a 1 MHz resolution. From these results, we confirmed that the CISPR measurement parameters are reasonable and effective.

We have developed an efficient iterative inversion method applicable to both two-dimensional (2D) and three-dimensional magnetotelluric data. The method approximates horizontal derivative terms with their values calculated from the fields of the previous iteration. The equations at each horizontal coordinate then become uncoupled. At each iteration this allows separate inversions for the improved conductivity profile beneath each measurement site. Resultant profiles are interpolated to form a new multidimensional model for which the fields for the next iteration are calculated. The method is extremely fast, and tests with 2D data show very promising results.

[1] One year of hydrogen sulfide measurements in an urban traffic site were used to assess the importance of traffic in the overall high ambient air burden of H2S (mean annual concentration of 8 μg/m3). During calm nighttime hours, hourly values of H2S were correlated positively with those of CO (R2 = 0.75) and SO2 (R2 = 0.70), suggesting a common source from traffic. For the driving conditions of the measurement site, H2S automotive emissions are around 24% w/w those of SO2, while European inventories calculate these at only 2.5%. H2S annual traffic emissions, based on the existing emission inventories for CO and SO2 are calculated at 0.199–0.311 × 10−3 Tg a−1 for Thessaloniki and are extrapolated to 0.030–0.0485 Tg a−1 for the EU15 countries and 2.6 Tg a−1 for Europe and Eurasia. It appears that traffic emissions make up a significant contribution to the global H2S budget.

[1] During the intensive observational periods of the BERLIOZ campaign (20 and 21 July 1998 and 3 August 1998), vertical profiles from 0 to 800 m above ground of O3, NO2, NOx, selected VOC, and meteorological parameters were measured by means of a comprehensive tethered balloon system at Papstthum, a rural site 50 north west of the city of Berlin. Every 2 hours a complete profile was obtained. The VOC were collected on charcoal tubes simultaneously at four different heights over time intervals of 3 hours. The measurement systems participated at the quality assurance measures of the BERLIOZ campaign and fully complied with the data quality objectives. The balloon data provide important information on the vertical gradients of the trace gases at Pabstthum and clearly identify the development of the boundary layer in the course of the day. This information is important for the interpretation of the radical measurements discussed in the accompanying publications. They also give insight in the vertical extent of air masses of different chemical regimes and their temporal evolution. During the morning hours of 20 July the evolution of the city plume passing the measurement site with a vertical extension of 800 m could be documented. Owing to degradation by the reaction with NO a reduced O3 concentration level was observed within the plume in the morning hours of 20 July. The highest peak concentrations of the campaign observed on ground level in the morning of 21 July could not be attributed to the Berlin city plume.