Balance of the Air Pollutant Mass Fluxes of a City

Balance of the Air Pollutant Mass Fluxes of a City:

First Results of Vertical Soundings within

the TFS-EVA Project in Augsburg 1998

A contribution to subproject GENEMIS

G Baumbach, K. Glaser and U. Vogt

Pfaffenwaldring 23, D -7 05 69 Stuttgart, Germany

Introduction

Emission inventories are generally based on emission calculations for which many assumptions have to be made. Since these assumptions introduce uncertainties concerning the correct emission rates, an independent method for measuring emission rates for a whole city area will be presented here. First results from the application of the method to experimental data are compared to results from calculated emission rates from the same area of investigation. The principle of the method is based on making a cross section both on the windward side and the leeward side of the area to be investigated (in case of the

TFS-EVA experiment, the city of Augsburg) and to determine the air pollutant mass flows passing through these cross sections. The difference between these two air pollutant mass flows yields the emission mass flows released in the area under investigation. During the TFS-EVA experiment in Augsburg in March and October 1998 the method will be applied to determine the emission rates of the city of Augsburg.

Results form the Neckarsulm/Heilbronn "Ozone Field Experiment"

The method for balancing air pollutant mass flows described above was applied on data from the "Ozone Field Experiment" carried out in the urban area of

Neckarsulm/Heilbronn, Germany, in 1994 (Neu, 1995). In Fig. 1 as an example the windward and the leeward vertical profiles of the temperature, wind speed and wind direction and the NO: concentration are shown. The vertical profiles originate from tethered balloon soundings. The balloon measurement systems and the relevant performance characteristics have been described in Baumbach et al. (1993; 1995). Fig. 2 displays the

842 G. Baumbach et al.

measurement sites and the area of investigation. In the vertical profiles in Fig. 1 at about 300 m above ground a marked temperature inversion is apparent which inhibits vertical exchange of air. Therefore emissions released near ground level only disperse up to the height of the inversion layer.

ozone experiment siarang numero. no starting time in Amorbach 09:15 a.m. Heilbronn/Neckarsulm 24.06.19S4 starting time in Wertwiesenpark 09:07 a. n

- - | - - ] j | - !- - |- \ - ^[ - - it c - I - / L Q. - leeward > m - 1] i - ,/f ] - f - - ji _...1 | 2^. .... I heigh t i n m abov e groun d leve l \ ! - 1^ L w u ) .& . e n O - < a : ) O C ) O C { 1 Ji , 1UU twind - ware 0- ,,; ,&,l,...l.,,,l ..,&. j" fA i j 1 1 i 10 15 20 5 1 D 15 0 5 10 15 S W N E S 0 10 20 0 50 10015 dry temperature mixing3 ratio wind speed wind direction NO2 Os in °C in g/kg in m/s in ppb in ppb

Fig. 1: Vertical profiles of a night time sounding windward and leeward simulataneously in Neckarsulm/Heilbronn 24.06.1994, 9 a.m.

This can be seen from the vertical profiles of the NOi concentrations both on the windward and the leeward side. For calculating mass flows the exact mixing height represents an important parameter which must be known at any time of the respective balancing period. The difference between the windward and the leeward NOi concentration identifies the increase of NO: caused by emissions in the area under investigation.

Suitable time periods for the calculation of mass balances were found on Sunday 26.6.1994 and on Monday 27.6.1994 in the afternoon between 12 a.m. and 15 p.m.. At these times the wind direction was fitted to the axis between the two measurement sites.

As a first step the air pollutant fluxes are calculated as fluxes through a column of a uniform with of 1 m by the equation on the following page.

The TFS-EVA Project in Augsburg 1998 843

m = I c - p- v • dh NO, J ^ 0

/77 pollutant flux in kg/(h m) c is the volume concentration in ppb p the gas density in |ig/jil v the horizontal wind velocity in m/s h the height above ground in m

Fig. 2: Investigation area and location of the measurement sites in Neckarsulm/ Heilbronn

The calculated fluxes of the component NO] are shown in Table 1 as a mean value of all sounding performed during the selected time period. The difference between the calculated fluxes yields the NO] flux from the urban area which amounts to 19 g/(h m) on Sunday afternoon and to 95 g/(h m) for Monday afternoon.

844 G. Baumbach et al.

Table. 1: Calculated fluxes of NOi in g/(h m) through a column of 1 m width as mean values during two selected time periods mass flux windward mass flux leeward difference of flux

in g/(h m) in g/(h m) lee and windward in g/(h m) Sunday, 26th June, 8 27 19

1994 Monday, 27th June, 52 147 95 1994

In order to obtain the flux of the entire urban area the flux referred to 1 m width must be multiplied with the mean width of the pollutant plume. Reading from the map also displaying the shape of the area of investigation the plume will be 5 km large. Of course multiplying by the width of the plume assumes that in both cross sections, windward and leeward even horizontal distributions are present. Thus the emission fluxes for the two selected time periods are determined. Table 2 shows the results. It also includes calculated emission rates based on an emission inventory (Neu U., 1995).

Table 2: Calculated fluxes of NO: in kg/h as mean values during two selected time periods

Emission rates based on Calculated emission rate measured fluxes in kg/h in kg/h

Sunday, 26th June, 95 86 1994 Monday, 27th June, 475 380 1994

The TFS-EVA project

An important improvement of the flux balancing method could be achieved if a more dense set of data from the windward and especially from the leeward cross section were available. The TFS-EVA project is designed to deliver the additional information required.

Fig. 3 schematically displays the design of an experiment and the measurement techniques to be applied for measuring air pollutant mass flows through the windward and the leeward cross sections. In both cross sections vertical and horizontal profiles of meteorological parameters and air pollutant concentrations have to be measured simultaneously in order to produce data with high spatial and temporal resolution. For the vertical profiles again several tethered balloon measurement systems are used. For horizontal profiles at the lower altitudes (about 300 m above ground) a remote control airship

The TFS-EVA Project in Augsburg 1998 845

equipped with similar measuring instruments to the tethered balloons is used

(Vogt Baumbach, 1995). Additional horizontal and vertical profiles are measured by aircraft operating in higher altitudes. The chemical species for which emission rates have to be determined are NO% and VOC. The measurements are accompanied by emission inventories for the results of calculated and measured emission rates and can be compared. The first measurement period took place in March 1998. Therefore here only first results from a pre-experiment in January 1998 can be presented. To obtain some knowledge of the local conditions and the concentration levels to be expected, vertical soundings at the leeward site were carried out. The fluxes referred to a column of 1 m width with 198g/(mh) as a mean value of all soundings between 9 a.m. and mid-day on January 12th, 1998.

Conclusions

Fig. 3: Equipment used in the EVA project in Augsburg

846 G. Baumbach et al.

The method for the determination of air pollutant emission rates for a whole city area shows encouraging results when it is applied on data from the "Ozone

Field Experiment". Therefore the results from the Augsburg experiment, which is specially designed for the mass flow balance can be expected to deliver a precise estimation of the emission rates which can be used for the evaluation of calculated emission rates.

References

Baumbach G, Baumann K, Grauer A, Semmler R, Steisslinger B, Wanner H, Kiinzle T and Neu U, A tethersonde measuring system for detection of O], NO], hydrocarbon concentrations, and meteorological parameters in the lower planetary boundary

layer, Meteorol Zeitschrift,N.¥. 2, 1993, 178-188 Baumbach G and Vogt U, A tethered-ballon measurement system for the determination of the spatial and temporal distribution of air pollutants such as Og, NO], VOC, particles and meteorological parameters, EUROTRAC Newsletter, 16/1995, 23-29 Vogt U and Baumbach G, Experimented Bestimmung des Transports von Luftverunreinigungen aus der Stadt Freiburg ins Zartener Becken (Dreisamtal) und umgekehrt, Universitat Stuttgart - ALS Jahresbericht 1995, 147 - 157

Neu U, Ozonversuch Neckarsulm/Heilbronn - Wissenschaftliche Auswertungen, ed. by Umweltministerium Baden-Wurttemberg (Germany) 1995