Atmospheric Particulate Matter in Urban Environments
A contribution to subproject SATURN
Tuomo Pakkanen, Christina Ojanen, Risto Hillamo,Päivi
Aarnio, Tarja
Koskentalo and
Willy Maenhaut
Finnish Meteorological Institute, Sahaajankatu 20 E, FIN-00810 Helsinki,
Finland
1. Summary
In this project concentrations of atmospheric particles and gases were
monitored and size-segregative aerosol sampling and detailed chemical analysis
combined with measurements of local weather conditions and air mass back-trajectories
were made. More than 60 chemical components were determined. Quality assurance
and quality control were introduced by making parallel sampling and analysis
using different types of size-segregative samplers and analysis methods.
2. Aim of the research
The aim of this contribution is to estimate source-receptor relationships,
gas-particle interactions and particle deposition in the Helsinki area.
The results of the project can be utilised in estimating health effects
of atmospheric particles, in planning emission abatement strategies and
in future research concerning atmospheric particles and gases.
3. Activities during the year
During 1998 the earlier measurement results from 1996-1997 were examined.
In September 1998 the final report (in Finnish) was ready. At present two
manuscripts are being prepared for international journals: 1) an
overview of the results entitled "Sources, chemical composition and size
distributions of inhalable particles in the Helsinki area" and, 2)
a more specific paper about black carbon entitled "Atmospheric black carbon
in Helsinki".
In March - April 1998 an intensive measurement campaign was made at
Vallila, an urban site in Helsinki. Concentrations of particulate components
and several gases were measured separately for mornings (6 - 12 am), afternoons
(noon - 6 pm) and for evenings and nights
(6 pm - 6 am).
4. Principal results
During April 1996 - June 1997 virtual impactor (VI, Loo and Cork, 1988)
measurements (Pakkanen et al., 1999) were made at Vallila, an urban site
in Helsinki, at Herttoniemi, a semi-urban site 7 km to the East from the
city centre, and at Luukki, a rural site 25 km North West from the city
centre. At Vallila and Luukki parallel Berner impactor (Berner and Lürzer,
1980) measurements were made once a month. It was observed that about 50%
of the sampled particulate ammonium nitrate evaporated from the filter
used for collection of particles in the VI instrument (see Figure 1). This
ammonium nitrate evaporation, corrected by using additional nylon filters
in the VI, was observed to represent about 9% of the PM2.5 mass. The average
yearly PM2.5 concentrations, corrected for the ammonium nitrate evaporation,
were 11.3 and 7.8 µg/m3 for Vallila and Luukki, respectively. At
Vallila the yearly average PM15 concentration was 23.1 µg/m3 and
at Luukki about 13 µg/m3. The higher PM2.5 concentration at Vallila
was mainly caused by local traffic that was found to be an important source
for black carbon, organic carbon, road dust and nitrate. At the urban Vallila
site the most important contributors to PM2.5 were sulphate (20%), black
carbon (19%), organic carbon (an estimation of 19%), nitrate (14%), ammonium
(9%), crustal material originating mostly from road dust (8%) and sea-salt
(3%). Water content was estimated to have been about 5%. In PM15 the most
important chemical component was crustal road dust contributing 28%.
On working days black carbon (BC) had a clear diurnal variation with
highest hourly-average concentrations occuring during morning rush hours
(2.7 µg/m3) and afternoon rush hours (1.8 µg/m3), as presented
in Figure 2. On Saturdays, Sundays and on public holidays such strong diurnal
variation was not observed, which indicates the importance of traffic (e.g.,
diesel vehicles) as a BC source.
Table 1 presents the yearly-average (based on 30-55 samples) concentrations
of selected elements measured in fine particles (PM2.5) at Vallila, Luukki
and Herttoniemi. The concentrations are mostly below those observed in
Central Europe.
5. Main conclusions
At the urban site Vallila traffic was by far the most important local source
for atmospheric particles. At Vallila the average chemical composition
of PM2.5 was sulphate 20%, black carbon 19%, organic carbon compounds (estimation
of 19%), nitrate 14%, ammonium 9% and crustal material 8%. At the rural
site Luukki the average chemical composition of PM2.5 was similar but sulphate
was slightly higher and nitrate and black carbon were lower. At Vallila
black carbon showed a clear diurnal variation on working days with highest
concentrations occuring during morning and afternoon rush hours. Ammonium
nitrate evaporation during sampling can cause a considerable underestimation
for PM2.5 measurements.
6. Aim for the coming year
In 1999 a 1-2 month intensive measurement campaign will be arranged. Sampling
times will be adjusted as short as possible but long enough to allow for
necessary chemical analyses. There is already data sets from earlier measurements
which will be studied in detail during the course of the project.
7. Acknowledgements
The authors thank the TEKES programs SIHTI2 and MOBILE, the Finnish Ministry
of Trade and Communications and the Ministry of the Environment for funding.
Several people working at the Finnish Meteorological Institute and at the
Helsinki Metropolitan Area Council are acknowledged for their help in installing
the measurement apparatus.
8.References
Berner, A. and C. Lürzer; Mass size distributions of traffic aerosols
at Vienna.
J. Phys. Chem. 84 (1980) 2079-2083.
Loo, B.W. and C.P. Cork; Development of high efficiency virtual impactors.
Aerosol Sci. Technol. 9 (1988) 167-176.
Pakkanen, T.A., R.E. Hillamo, M. Aurela, H.V. Andersen, L. Grundahl,
M. Ferm, K. Persson, V. Karlsson,
A. Reissell, O. Royset, I. Floisand, P. Oyola and T. Ganko; Nordic
intercomparison for measurement of
major atmospheric nitrogen compounds. J. Aerosol Sci.
30 (1999) 247-263.
Table 1. Average (and standard deviation) and median concentrations
of selected elements
in fine particles as ng/m3.
Figure 1. Evaporation percentage of nitrate from the filter sampling
particles in the VI.
Figure2. Hourly-average concentrations of black carbon during various
days at Vallila.