S. Gilge

Strong daytime production of OH from HNO2 at a rural mountain site

Nitrous acid and OH were measured concurrently with a number of other atmospheric components and relevant photolysis frequencies during two campaigns at the Meteorological Observatory Hohenpeissenberg (980 m a.s.l.) in summer 2002 and 2004. On most of the 26 measurement days the HNO 2 concentration surprisingly showed a broad maximum around noon (on average 100 pptv) and much lower concentrations during the night (∼30 pptv). The results indicate a strong unknown daytime source of HNO 2 with a production rate on the order of 2-4 x 10 6 cm -3 s -1 . The data demonstrate an important contribution of HNO 2 to local HO x levels over the entire day, comparable with the photolysis of O 3 and HCHO. On average during the 2004 campaign, 42% of integrated photolytic HO x formation is attributable to HNO 2 photolysis.

Temporal and spatial structure of a volcanic ash cloud: ground-based remote sensing and numerical modeling

The Eyjafjallajökull volcano eruptions during mid April 2010 influenced European air traffic basically. This was mainly due to the low melting point of ejected material and the sharp-edged form of particles. As there is the necessity to understand the dispersion of such an ash cloud we assess the existing measurement networks and evaluate the existing numerical models (MCCM). We use data from ceilometers to detect the vertical distribution of the volcanic cloud. Ground-based in situ measurements of particle concentrations, sulphur dioxide and further parameters complete the data basis. The analysis concentrates on the spatial and temporal features of the event over Southern Germany. It is an initiative of a scientific cooperation on aerosols in the area of Augsburg (500 m altitude) - Munich (550 m) - Hohenpeißenberg (1000 m) - Zugspitze / Schneefernerhaus (2650 m). The period from the evening of April 15th to the evening of April 20th, 2010 is covered. Main emphasis is laid on shorter events: (1) the first 15 hours of April 17th when the first cloud moved over Southern Germany, (2) the night from April 17th to April 18th when a second puff arrived over Southern Germany, and (3) the afternoon of April 19th when another puff arrived over Southern Germany. Back trajectories are used to check the origin of the observed dust clouds. Results from the model simulations with MCCM for the whole period will be compared with the measurement results. We will draw conclusions about the predictability of such events, the abilities of numerical models, the possible relevance for near-surface air quality as well as the possible enhancements of existing observation networks and simulation systems.

A case of transatlantic aerosol transport detected at the Schneefernerhaus Observatory (2650 m) on the northern edge of the Alps

An unusual peak in atmospheric aerosol particle number and mass concentration occurred on September 20 and 21, 2006 at the Schneefernerhaus (SFH) Observatory, Germany. A source-receptor analysis using the Lagrangian transport model FLEXPART suggested that polluted air from source regions in the Western and Central U.S. travelled within 4—8 days over the Atlantic to the European Alpine region. A warm conveyor belt over the northern Great Plains was identified as the essential process lifting the boundary layer air to the high altitudes required for a rapid transatlantic transit. The layer arriving at SFH had an aerosol mass concentration of about 30 μg m -3 , and a particle number size distribution showing an aged accumulation mode aerosol with mode diameter around 0.3 μm. A combination of in-situ humidity, 214 Po and carbon monoxide measurements as well as upper air observations (radiosoundings) suggested that the layer had no previous contact with the local/European boundary layer. A screening of three years of FLEXPART simulations (2005-2007) yielded this case study as the only event of transatlantic anthropogenic aerosol to SFH where mixing with the boundary layer could safely be excluded. The event therefore represents rare surface-based evidence of transatlantic transport of fine and ultrafine aerosols.

A European-wide 222Radon and 222Radon progeny comparison study [Dataset]

Although atmospheric 222Radon (222Rn) activity concentration measurements are currently performed world-wide, they are being made by many different laboratories and with fundamentally different measurement principles, so compatibility issues can limit their utility for regional-to-global applications. Consequently, we conducted a European‐wide 222Rn/222Rn progeny comparison study in order to evaluate the different measurement systems in use, determine potential systematic biases between them, and estimate correction factors that could be applied to harmonize data for their use as a tracer in atmospheric applications. Two compact portable Heidelberg Radon Monitors (HRM) were moved around to run for at least one month at each of the nine European measurement stations included in this comparison. Linear regressions between parallel data sets were calculated, yielding correction factors rela tive to the HRM ranging from 0.68 to 1.45. A calibration bias between ANSTO (Australian Nuclear Science and Technology Organisation) two‐filter radon monitors and the HRM of ANSTO/HRM = 1.11±0.05 was found. Moreover, for the continental stations using one‐filter systems that derive atmospheric 222Rn activity concentrations from measured atmospheric progeny activity concentrations, preliminary 214Po/222Rn disequilibrium values were also estimated. Mean station-specific disequilibrium values between 0.8 at mountain sites (e.g. Schauinsland) and 0.9 at non‐mountain sites for sampling heights around 20 to 30 m above ground level were determined. The respective corrections for calibration biases and disequilibrium derived in this study need to be applied to obtain a compatible European atmospheric 222Rn data set for use in quantitative applications, such as regional model intercomparison and validation, or trace gas flux estimates with the Radon‐Tracer‐Method.