Size segregated particle mass concentration and chemical composition in an agrarian region in Saxony G. Spindler, K. Müller, E. Brüggemann, H. Herrmann
Abstract
Zusammenfassung
For a period of nine years (1993 to 2001) daily filter samples PM10 were collected by a high volume sampler (HV) and weekly filter samples PM10, PM2.5, and PM1 were collected additionally from 1999 by a low flow sampler (LF) at the IfT-research station Melpitz in the downstream plume of the Leipzig conurbation. The measuring site is located near the village Melpitz in the vicinity of the city Torgau in the river Elbe valley. The site is placed on a flat 100years-old meadow surrounded by agricultural land. For the whole time period the particle mass concentration PM10 shows a decreasing trend in the daily HV samples. Highest values have been observed in the winters before winter 1997/98. In the following winters no pronounced concentration peaks were found. A reason is the decreasing number of coal heating systems in the Leipzig conurbation. Additionally, in the last winters high pressure systems with transport of dry continental air masses and low mixing heights relatively seldom occurred. The NO3-/SO42--ratio shows an increasing trend with seasonal variation, caused by the decreasing SO42-mass concentration in PM10 which originates in the strong decrease of SO2 concentration, but also in NH4NO3-losses by evaporation from the filters during higher temperatures in summer. From the weekly LF samples the contribution of PM2.5 and PM1 to PM10 (100%) can be estimated. Most of the PM2.5 mass is PM1. During summers the mass of coarse particles (PM10 – PM2.5) is higher than in other seasons. One reason could be found in the occurrence of longer periods of dry ground surfaces with re-emission of crustal and biological material by turbulence, other reasons are agricultural activity and moving cars on dry roads. The HV mass concentration measurements were integrated in a longer historical mass trend (since 1983) for Saxony.
Größenaufgelöste Massenkonzentration und chemische Zusammensetzung von Partikeln in einer ländlichen Region Sachsens
Keywords: PM10, PM2..5, PM1, main constituents, long term trend, seasonal variations _______ 1) postcode :
Gerald Spindler, Institut für Troposphärenforschung e.V., Permoserstrasse 15, 04318 Leipzig, Germany e-mail:
[email protected]
In neun Jahren (1993 bis 2000) wurden täglich mit einem Partikelsammler (hoher Volumenstrom, HV) PM10 Filterproben gesammelt. Zusätzlich erfolgte ab 1999 die Sammlung wöchentlicher Proben für PM10, PM2,5 und PM1 mit einem geringen Volumenstrom (LF) an der Forschungsstation des IfT in Melpitz im Abluftbereich des Ballungszentrums Leipzig. Der Standort befindet sich nahe dem Dorf Melpitz (Stadt Torgau) im Urstromtal der Elbe. Die Station wurde auf einer flachen 100jährigen Weide, die von Agrarland umgeben ist, errichtet. Für die gesamte Zeit zeigt die Partikelmassenkonzentration PM10 einen fallenden Trend in den täglichen PM10-Proben (HV). Die höchsten Konzentrationen wurden in den Wintern vor dem Winter 1997/98 beobachtet. In den folgenden Wintern wurden keine auffälligen Konzentrationsmaxima registriert. Ein Grund dafür ist die sinkende Anzahl von einzelnen Braunkohlefeuerstätten im Leipziger Ballungsraum. Zusätzlich traten winterliche Hochdruckwetterlagen mit Transport trockener kontinentaler Luftmassen und niedrigen Mischungsschichthöhen seltener auf. Das NO3-/SO42-Verhältnis zeigt einen fallenden Trend mit jahreszeitlichen Variationen, verursacht durch eine fallende Sulfatkonzentration, aber auch durch Verdampfung von NH4NO3 vom Filter bei höheren Temperaturen. Von den wöchentlichen LF-Filtern kann der Anteil von PM2,5 und PM1 am PM10 (100%) abgeschätzt werden. Der größte Teil der PM2,5-Masse ist PM1. Im Sommer ist der Massenanteil des Grobstaubes (PM10PM2.5) größer als in anderen Jahreszeiten. Eine Ursache sind im Sommer längere Trockenzeiten mit Winderosion, andere Ursachen liegen in der landwirtschaftlichen Aktivität und Aufwirbelungen verursacht von fahrenden Autos auf trockenen Straßen. Der Verlauf der Partikelmassenkonzentration (HV) wurde in eine 1983 beginnende Messreihe für Sachsen integriert. Schlüsselworte: PM10, PM2,5, standteile, Langzeittrend, Variabilitäten
PM1, Hauptbejahreszeitliche
Introduction Up to the end of the 80-ies the region around Leipzig was one of the most polluted areas in Central Europe. Starting in 1991 the national research project SANA (Scientific Programme on Recovery of the Atmosphere above the New Federal States of Germany) was established to investigate the changes in air quality. The collection and characterisation of environmental particulate matter is in the focus of atmospheric sciences, human health and environmental policy for several years. Nevertheless, the present knowledge on the primary formation, source identification and the effects of particulate matter is unsufficently. At the research station Melpitz (downwinds of the conurbation Leipzig-Halle-Merseburg) the input of mainly anthropogenic aerosols and other pollutants into an agrarian region was investigated from the year 1992 on beside the dry deposition of gaseous species and the wet deposition of pollutants. Beginning in summer 1992 daily samples of PM10 have been collected (Müller, 1999). PM2.5 and PM1 (Spindler et al., 1999) sampling started in 1995 and 1999, respectively. Long time series of measurements and investigations are the observational basis for the distinction of real atmospheric changes and short weather related events in the atmosphere (Heintzenberg et al., 1998). Water soluble ions, the carbonaceous material, insoluble crustal material and water are the most important constituents. Whereas for the climatic effects the black carbon is the main component the organic material is the most interesting for human health effects and otherwise for agricultural effects the ionic constituents have important influences (Heintzenberg, 1989,. Neusüß et al., 2000). The physical properties of particles - diameter and humidity growth - are of relevance for their lifetime, cloud processing and transportation effects (Swietlicki et al., 2000). Characterisation of sampling site and methods The background particle concentration was measured continuously at the IfT research station in Melpitz (Altitude 87 m, Latitude 51°32’N, Longitude 12°54’E, for detailed site description see Spindler et.al., 2001) in the downstream plume of the Leipzig conurbation. An comparison between PM10 HV daily samples and PM10 LF weekly samples looks quite well (Spindler, et al., 1999). The HV sampler is a modified Sierra Anderson-PM10 sampler (Anderson Samplers Inc., USA) with quartz fibre filters (25.4 x 20.3 cm, Type MK 360, Munktell Filter, Sweden). The sampling time for each day was over 23.5 hours from 08:00 to 07:30 CET (central European time). The sampling inlet was in a height of
1.5 m over ground, the sampling volume was approximately 1340 m³. The LF sampler is the Partisol 2000 Air Sampler (Rupprecht and Patashnik Co. Inc., USA). For the weekly filter samples PM10, PM2.5 and PM1 Teflon filters with 47 mm diameter (Millipore, Eschborn, Germany, Type 4700, 3 µm pore size) were used. The weekly sampling volume is 84 m³. Both particle samplers realise the cut-offs with a virtual impactor. The particle mass concentration was determined for both samplers by weighing under constant conditions (50% relative humidity, temperature 20°C). After a conditioning time of 24 hours in minimum the particle mass was determined gravimetrically (Mettler AT 261 Delta Range balance, Mettler Toledo GmbH, Germeny). The content of water soluble ions were determined from a quarter of the HV filters or a half of the LF filters, respectively. by standard ion chromatography procedure. Columns from Dionex, USA were used. Long term trends in PM10 Continous TSP sampling was established in 1983 by the meteorological Service of the GDR. The existing data set of Saxonian measurements was connected to the measurements of PM10 in Melpitz (Spindler et al., 1999). The reconstructed data (source: Sächsisches Landesamt für Umwelt und Geologie) for 1983 to 1990 present a wide scatter with mean values between 60 and 80 µg m-3 at rural sites. The yearly mean mass concentration decreased to 21.8 µg m-3 in 2000. Chemical analyses for the PM constitution do not exist for the historical data. An extrapolation of the known data on SO2 and the data from the early 90-ies allows to speculate that sulphate was the most important ionic part of the PM. Beside the sulphate also fly ash from lignite fired power plants, industrial plants and households was a major component of the aerosol with important contents of salts, soot and metal oxides. Beginning in the 90-ies the switch off or the modernization of power plants and industrial sources as well as the individual household heating systems led to a rapid decrease of anthropogenic emissions of PM despite the increase of road traffic emissions (Figure 1). Daily mean concentrations of PM10 reached in the winter 1993/94 15 times values above 100 µg m-3 whereas in the last three winters at no time. Otherwise in the last winters high pressure systems with transport of dry continental air masses and low mixing heights relatively seldom occurred. In Figure 2 the comparison of the yearly mean PM10 constitution from 1993 and 2000 documents the significant loss of sulphate and calcium and the relative increase of nitrate and ammonium at nearly constant concentrations. The non specified remainder seems to be constant but the carbon (organic and
100 daily mean (HV)
particle mass concentration [µg/m³]
90
10 day running mean
80 70 y = - 0.01x + 40.0, n = 3386
60 50 40 30 20 10 0 01.01.93
01.01.94
01.01.95
01.01.96
01.01.97
01.01.98
01.01.99
01.01.00
01.01.01
01.01.02
Figure 1: PM10 (HV) nine year course at the Melpitz site. The ellipses highlight pronounced winter concentration peaks
21.7 7.77
1993
2000
1.82
13.52
4.75
% 6.47 Nitrate % Sulfate % Ammonium % Calcium % further Ions % Crustal/Carbon/Water
9.49 1.09
14.14
5.17
56.59 57.51
6
0.00
5
0.50
4
3
1.00
NO3-/SO4-SO4--/2*NH4+ NO3-/NH4+
1.50
2
2.00
1
2.50
0 01.01.93
3.00
01.01.94
01.01.95
01.01.96
01.01.97
01.01.98
01.01.99
01.01.00
01.01.01
01.01.02
Figure 3: Nine year course of 10 day running means of molar ratios in PM10 at the Melpitz site (the ratios for nitrate to sulphate and sulphate to ammonium plotted at the right y-axis as invers)
molar ratio [(SO4--/2*NH4+) and (NO3-/NH4+)]
molar ratio [NO3-/SO4--]
Figure 2: Comparison of ionic components of PM10 in Melpitz between the years 1993 and 2000 (basis: daily samples from the HV-sampler). The area of the two circles represents the mean particle mass
elemental) is decreasing while the crustal components increased by more dry and warmer summers during the last years. From 1993 to 2000 the decrease of PM concentrations led to a decreasing deposition of mineral components as sulphur and calcium into the agricultural used land. During the last decade a change of the most important ion from sulphate to nitrate occurred (Figure 3). The seasonal variation of the nitrate content determined in the filter samples depends on the evaporation of NH4NO3 during higher temperatures (Schaap et al., 2001) from the used quartz fibre filters and the displacement of the gas-particle equilibrium, additionally. The ammonium concentrations are nearly stable during the seasons.
more coarse mode particles exist, because surfaces, especially covered with short vegetation, dry faster (Klemm et al., 2002) and the absolute precipitation is lower and more intensive as in other seasons. Coarse particles caused from re-emission by turbulences and agricultural activities in the surroundings, transported only over short distances in a local area, because they have a relatively high deposition velocity. The size fraction (PM2.5-PM1) shows the smallest particle mass concentration over the whole year, that means the most of the PM2.5 is PM1. Table 2 lists the contribution of the mean water soluble ions to the mass of the three particle fractions for all three investigated years. Sulphate and ammonium have the highest contribution to the fine particles, as result of a long range transport from natural and anthropogenic sources and particle modification by gas to particle conversion. Nitrate has the highest part of mass in the fine and medium particles. This gives a hint that combustion processes are an important source. But also the exchange of chloride during the transport from the sea to the more continental measurement site plays a roll caused by different multiphase chemical processes (ten Brink, 1998). The lowest content of water soluble ions in the coarse particles indicates re-emitted crustal material. All discussed results of this long time study are from filter measurements, therefore in the summer losses of ammonium nitrate (sulphate) by evaporisation caused from high temperatures and low relative humidity can reduce the mass of fine and medium particles, especially.
Size segregated composition PM10, PM2.5 and PM1 The particle mass concentration and the mass of water soluble ions are available as weekly means for three particle size fractions (aerodynamic diameter PM1: fine particles, PM2.5-PM1: medium particles and PM10-PM2.5: coarse particles) from the LF sampler. Table 1 lists the contribution of PM2.5 and PM1 to PM10 (100%) with a distinction between summer and winter time for 1999 to 2001. Figure 4 shows an detailed example of the mass distribution in the particle fractions for the whole year 2000 together with the daily sum of precipitation. The yearly course of the mass concentration distribution between the size fractions demonstrates the absolute maximum for the largest particles only in summer time. In summers
Table 1:
Mass contribution of PM2.5 and PM1 to PM10 (100%) distinguished between winter (October to March) and summer (April to September) for the years 1999, 2000 and 2001
1999
summer 2000
2001
1999
winter 2000
2001
PM2.5
56.7 %
56.8 %
65.2 %
82.0 %
76.4 %
82.8 %
PM1
46.2 %
47.4 %
50.0 %
62.9 %
56.6 %
59.4 %
PM
Table 2:
Relative mass contribution of the mean water soluble ions to the mass of the three particle fractions (mean for 1999 to 2001)
water soluble ion (% of particle fraction)
particle fraction (absolute mass of PM10 for PM10=100%) PM1 (54.4 %)
PM2.5-PM1 (15.3 %)
PM10-PM2.5 (30.3 %)
2-
21.9 %
13.9 %
5.8 %
NH4+
12.9 %
9.95 %
1.8 %
NO3
-
15.9 %
21.2 %
9.1 %
sum
50.7 %
45.0 %
16.7 %
SO4
0
45 40
5
10 30 25
15
20
20
precipitation [mm]
mass concentration [µg/m³]
35
15 25 10 5
30 PM1
PM2.5-PM1
PM10-PM2.5
daily precipitation
35
0 Jan
Feb
Mrz
Apr
Mai
Jun
Jul
Aug
Sep
Okt
Nov
Dez
Figure 4: Example of the mass distribution in the particle fractions for the year 2000, the daily sum of precipitation plotted at the right y-axis as invers. (week 18 interpolated and weeks 14 and 15 are calculated from daily measurements)
Acknowledgements We wish to thank the European Community (within the LIFE programme, the Saxonian State Ministry for Environment and Agriculture (SLUG138802.3521/46) for funding projects. The measurements were continued in the framework of the national research program AFO2000 (project VERTIKO) We are greatly indebted to J. Hanss and A. Grüner for the reliable measurements, for the numerous analysis we thank E. Neumann, A. Thomas, H. Bachmann and A. Kappe. References Heintzenberg J (1989) Fine particles in the global troposphere, A review. Tellus 41B, 149-160 Heintzenberg J, Müller K, Birmili W, Spindler G, Wiedensohler A, (1998) Mass related aerosol properties over the Leipzig Basin. J. Geophys. Res., 103, 13,125-13,335 Klemm O, Milford C, Sutton M A, Spindler G, van Putten E (2002) A climatology of leaf surface wetness. Theor. Appl. Climatol. 71, 107-117 Müller K (1999) A 3-year study of the aerosol in Northwest Saxony (Germany), Atmos. Environ. 33, 1679-1685 Neusüß C, Pelzing, A, Plewka, A, Herrmann, H (2000) A new analytical approach for size-resolved specification of organic compounds in atmospheric aerosol particles: Methods and first results. J. Geophys.Res. 105, 4513-4527
Schaap M, ten Brink H M, Müller K, (2001) The European nitrate distribution as deduced from quality assured measurements. J. Aerosol. Sci. 32, Suppl. 1, S671-S672 Spindler G, Müller K, Herrmann H, (1999) Main particulate matter components in Saxony (Germany) – trends and sampling aspects. ESPR – Environ. Sci. & Pollut. Res. 6(2) 89-94 Spindler G, Teichmann U, Sutton M A (2001) Ammonia dry deposition over grassland – micrometeorological fluxgradient measurements and bidirectional flux calculations using an inferential model. Q.J.R. Meteorol.Soc. 127, 795-814 Swietlicki E, Zhou J, Covert D S, Hämeri, K, Busch B, Väkevä M, Dusek U, Berg O H, Wiedensohler A, Aalto P, Mäkelä J, Martinsson B G, Papaspiropoulos G, Mentes B, Frank G, Stratmann F (2000) Hygroscopic properties of aerosol particles in the north-eastern Atlantic during ACE-2. Tellus 52B, 201-227.
