Comprehensive assessment of meteorological conditions and airflow connectivity during HCCT-2010

Abstract

This study presents a comprehensive assessment of the meteorological conditions and atmospheric flow during the Lagrangian-type "Hill Cap Cloud Thuringia 2010" experiment (HCCT-2010), which was performed in September and October 2010 at Mt. Schmucke in the Thuringian Forest, Germany and which used observations at three measurement sites (upwind, in-cloud, and downwind) to study physical and chemical aerosol-cloud interactions. A Lagrangian-type hill cap cloud experiment requires not only suitable cloud conditions but also connected airflow conditions (i.e. representative air masses at the different measurement sites). The primary goal of the present study was to identify time periods during the 6-week duration of the experiment in which these conditions were fulfilled and therefore which are suitable for use in further data examinations. The following topics were studied in detail: (i) the general synoptic weather situations, including the mesoscale flow conditions, (ii) local meteorological conditions and (iii) local flow conditions. The latter were investigated by means of statistical analyses using best-available quasi-inert tracers, SF6 tracer experiments in the experiment area, and regional modelling. This study represents the first application of comprehensive analyses using statistical measures such as the coefficient of divergence (COD) and the cross-correlation in the context of a Lagrangian-type hill cap cloud experiment. This comprehensive examination of local flow connectivity yielded a total of 14 full-cloud events (FCEs), which are defined as periods during which all connected flow and cloud criteria for a suitable Lagrangian-type experiment were fulfilled, and 15 non-cloud events (NCEs), which are defined as periods with connected flow but no cloud at the summit site, and which can be used as reference cases. The overall evaluation of the identified FCEs provides the basis for subsequent investigations of the measured chemical and physical data during HCCT-2010 (see http://www.atmos-chem-phys.net/special_issue287.html). Results obtained from the statistical flow analyses and regional-scale modelling performed in this study indicate the existence of a strong link between the three measurement sites during the FCEs and NCEs, particularly under conditions of constant southwesterly flow, high wind speeds and slightly stable stratification. COD analyses performed using continuous measurements of ozone and particle (49 nm diameter size bin) concentrations at the three sites revealed, particularly for COD values <0.1, very consistent time series (i.e. close links between air masses at the different sites). The regional-scale model simulations provided support for the findings of the other flow condition analyses. Cross-correlation analyses revealed typical overflow times of similar to 15-30 min between the upwind and downwind valley sites under connected flow conditions. The results described here, together with those obtained from the SF6 tracer experiments performed during the experiment, clearly demons...

Trace metal characterization of aerosol particles and cloud water during HCCT 2010

“…Entrainment of cleaner air from above might also reduce concentrations or, in the case of more polluted air mass from above, increases the concentration. However, during HCCT, the meteorological analysis as reported by Tilgner et al (2014) did not show strong entrainment from more polluted air masses especially during the selected events. In Fig.…”

“…Cr, Cu, and Ni concentrations were found to be higher at GB. Although entrainment of more polluted air masses may lead to an increase in the concentration of trace metals in the downwind site, meteorological studies by Tilgner et al (2014) revealed a more stable stratification during this event with no large differences observed in the coefficient of divergence of the particles, suggesting that the possibility of entrainment of polluted air masses from above was rather low. These increased trace metals are often found from traffic emissions relating to car brake wear (Maenhaut et al, 2005) or from fuel combustion (Lee and Vonlehmd, 1973).…”

“…Schmücke while aerosol particle sampling was conducted at the valley stations. A detailed description of the experiment, sampling site, and meteorological conditions during the experiment has been reported by Tilgner et al (2014).…”

“…The aim was to characterize the trace metal content in the aerosol before and after the particles interact with the cloud and also in cloud water in order to investigate the role of trace metals in altering the chemical composition of the cloud and the properties of the particles after passing through the cloud. Four full cloud events (FCEs) during which the air mass was found to have traveled through all three stations and the strict criteria of the experiment were fulfilled as described in Tilgner et al (2014) were chosen. In this study the temporal variation of the trace metals during the selected FCEs and the changes in trace metal particle size distribution and their properties after the passage of the particles through the cloud will be presented.…”

Measurements of PM10 ions and trace gases with the online system MARGA at the research station Melpitz in Germany – A five-year study

“…In autumn 2010, the MARGA participated in the HCCT 2010 campaign in Goldlauter for two months (Tilgner et al 2014) and in an international CEN (European Committee for Standardization) field measurement campaign at the UBA site, Waldhof, from May until July 2014. Further data losses appeared due to maintenance and technical issues.…”