Long-lasting research infrastructures covering the research areas of atmospheric chemistry, meteorology and climatology are of highest importance. The Atmospheric Station (AS) Křešín u Pacova, central Czech Republic, is focused on monitoring of the occurence and long-range transport of greenhouse gases, atmospheric aerosols, selected gaseous atmospheric pollutants and basic meteorological characteristics. The AS and its 250 m tall tower was built according to the recommendations of the Integrated Carbon Observation System (ICOS) and cooperates with numerous national and international projects and monitoring programmes. First measurements conducted at ground started in 2012, vertical profile measurements were added in 2013. A seasonal variability with slightly higher autumn and winter concentrations of elemental and organic carbon was revealed. The suitability of the doubly left-censored Weibull distribution for modelling and interpretation of elemental carbon concentrations, which are often lower than instrumental quantification limits, was verified. Initial data analysis also suggests that in summer, the tower top at 250 m is frequently above the nocturnal surface inversions, thus being decoupled from local influences.
Masts, towers and other tall constructions are used for meteorological measurements and planetary boundary layer studies since the 19th century (Monna and Bosveld, 2013). In the 1990s, tall towers started to be used as part of the greenhouse gas (GHG) observational infrastructure. Currently, the ICOS (Integrated Carbon Observation System) infrastructure is being built in Europe and a network of tall towers forms a central element of this research and monitoring infrastructure. Tall towers allow to obtain atmospheric observations that are representative for a larger region because placement of measurements at higher altitudes above ground minimizes the influence of very local fluxes on the observations (Bakwin et al., 1998; Haszpra et al., 2012). Measurements at tall towers also overcome the problem of complicated airflow in the lowermost 100–200 m of the planetary boundary layer (Stull, 1988). The same benefit is obtained for measurements of atmospheric pollutants such as tropospheric ozone or aerosols at tall tower sites.
Basic set of parameters measured at the Atmospheric Station Křešín u Pacova.
The Atmospheric Station (AS) Křešín u Pacova (49
The AS is primarily designed to become an ICOS Level 1 station (required
measurements are listed in the first six rows in Table 1). To fully exploit
the infrastructure potential, selected air quality parameters were added to
the list of measurement parameters (Table 1). Further long-term or campaign
measurements may be added in future (e.g. halocarbons, isotopes in
non-CO
Air samples for GHG determination are transported in permanently flushed
lines from different tower heights (Table 1) to analyzers placed in an
air-conditioned ground based container. On the contrary, ozone and mercury
analyzers are placed directly on the tower in an air-conditioned container
installed at 230 m height directly on the mast body and in air-conditioned
racks placed on platforms at 10, 50 and 125 m heights. This is because a
long inlet system and analyzer on the ground may lead to large sample losses
for these species (Galbally and Schultz, 2013). Aerosol instruments are
placed in the ground-based container. Meteorological sensors are installed
on 3 m long arms directed approximately south west (azimuth 215
Two pilot studies were conducted on two selected datasets. Organic and
elemental carbon (OC and EC, respectively), as important climate change
drivers (Penner et al., 1998), were measured from August to December 2013 by
a field semi-online OC/EC analyser (Sunset Laboratory Inc., USA) using a
PM
EC data was used to investigate the occurrence of censored observations at
the site, i.e. measurements under instrumental limits of detection and
quantification (0.2 and 0.5
Time series of organic carbon (OC), elemental carbon (EC) and the
ratio EC
Daily course of summer medians of bulk vertical temperature gradient across three layers.
Vertical temperature profile for the stability class of
significant surface inversions (between
One minute averages (mean of 4 values, reading every 15 s) of temperature
measured by the Vaisala HMP155 instrument at 10, 50, 125 and 240 m in the
period 11 June–10 September 2014 (summer season) were investigated. Only
those data were selected when records for all 4 measurement levels were
available (92 % of the whole period length). Vertical temperature
gradients – (
EC and OC concentrations are slightly higher in autumn and winter 2013
(average of 0.76 and 0.70
The statistical methods based on censored samples were used for the analysis
of EC measurements which contain a significant number of censored
observations. A good example is the week of 21–27 October 2013, which
contained approximately 25 % of concentration data lower than or equal to
0.5
Medians of the vertical temperature gradient in three layers (Fig. 2) reveal a typical summer daily course (Stull, 1988) although the plot is created from the whole summer dataset covering all weather conditions. Surface inversions dominate during nighttime, whereas the daytime is characterized by a convective boundary layer (CBL) with unstable stratification in the lower layer (10–50 m) and near-neutral stratification above. The lower layer has the largest diurnal amplitude of the temperature gradient, which crosses the adiabatic value early in the morning (preceded by the inversion destruction in this layer), reaches its maximum in the late morning, and again crosses the adiabatic value in the late afternoon.
An example of the vertical temperature profile is given in Fig. 3 for the
class of significant surface inversions (between
More pilot studies than presented here have to be conducted before regular monitoring and data interpretation can be started. General quality assurance, quality control and data validation procedures defined for monitoring programmes (e.g. Galbally and Schultz, 2013) have to be adjusted to the AS Křešín u Pacova particular conditions. Also, a tall tower concentration footprint (Vesala et al., 2008) for all sampling heights has to be calculated. Dynamics of the plantery boundary layer at the site and vertical gradients of meteorological parameters have to be studied. All this is currently under investigation.
Together with the adjacent Košetice Observatory, the AS forms the Colocated Station Košetice – Křešín u Pacova. Its manifold research infrastructure supports and claims for a multidisciplinary research approach. An important feature is also the combination of measurements for several atmospheric programs including GHGs, aerosols and gaseous pollutants with accompanying meteorological measurements. This preludes the monitoring supersites envisioned in the coming years. The AS Křešín u Pacova is an open access research infrastructure, proposals for collaborations are welcome.
This work was supported by the Ministry of Education, Youth and Sports of the Czech Republic within the National Sustainability Program I (NPU I), grant number LO1415. Edited by: F. Beyrich Reviewed by: J. Keder and M. Schumacher