Deposition is the phenomenon by which the atmosphere cleans itself.
It consists of the interchange of pollutant flows which occur at the earth's
surface. It is the mechanism through which pollutants (chemically altered
or not) return to the earth.
In the majority of cases it is efficient enough but there are some pollutants such as CO2 which show signs of a global increase due to the large emissions of pollutants from both natural and anthropogenic sources. There are two types of deposition mechanisms differentiated by the state of
There are two methods for calculating deposition flow from data measured
OBJECTIVESThe principal aim of the project is to develop a piece of
software with which to record valid data for the calculation of dry deposition
flows for NO-NO2-NOx and SO2.
The software will be developed based on an existing system which has
already been used for several measuring series.
In order to develop the software it is necessary to previously carry
out a series of studies:
Other subsequent objectives which could follow on from the project would
be to carry out a parameterization of the dry deposition flows using the
data collected as well as the testing and validating of existing deposition
models comparing their predictions with the data produced by the developed
The friction velocity u* quantifies the fluctuations of turbulence velocity
in the air, the scale concentration c* quantifies the fluctuations of a
pollutant's concentration. From the friction velocity and the concentration
scale we define the flow of a pollutant as:
In neutral conditions, wind speed increases logarithmically above the
zero plane, obtaining the standard equation of wind profiles which, adding
the stability function FM
where k is von Karman's constant, established experimentally at 0.4,
z the height above the zero plane and L Monin-Obhukhov's longitude.
In the same way, the concentration scale c* can be defined as:
The stability functions FH
have been experimentally estimated after much work and can be found in
Although the flow could be calculated from the equations described above, given the non linearity of the gradient with height, the differential method is particularly unsuitable in certain cases. The correct application of the differential method requires a vertical concentration profile on
three or more points above the surface. If we can only measure at two
heights we have an alternative procedure consisting of integrating equations
(2) and (3) between points z1 and z2, both above the surface. The resulting
in which YM and YH
are the integrated stability functions for momentum and heat respectively.
Therefore, having wind and concentration measurements at two heights
(z1 and z2) and knowing L, we can calculate both u* and c* and thus through
equation (1) obtain the flow of a pollutant.
HARDWARE AND SOFTWARE
In this project we have used the following instrumentation:
In particular, our software records pollutant measures at two heights since u* and L are obtained from a piece of software, developed in parallel, which uses "fast" measurement instruments.
At a fixed time interval, called the cycle time, the software gives
the mean of the pollutant measurements recorded at the two levels. The
software manages an air suction system at two heights and alternates between
the two levels during the cycle time.
The software requires timing parameters wich are read from a setup file:
The software calculations can be obtained through output files, although
we can see the data which the software receives at any point in time or
the data calculated in the last cycle, through a graphical web interface.
The software allows to calculate SO2, NO, NO2 and NOx concentration fluxes from the data stored in the output files. Calculated data:
Posible ampliations for the software are: