Transcript Online measurements of chemical composition and size

Online measurements of chemical
composition and size distribution of
submicron aerosol particles in east
Baltic region
Inga Rimšelytė
Institute of Physics
Vilnius, Lithuania
Research interests:
• The continuous study of these aerosol particles concentration, size and
chemical composition is therefore imperative for better understanding the
environmental effects of the atmospheric particles, as well as their sources,
formation and transformation processes. PM, especially the fine fraction,
remains airborne for long time in the atmosphere and can travel for
hundreds or even thousands of kilometers. Owing to chemical reactions,
condensation and accumulation, the particle change their chemical
composition, mass and size. The fact that PM can travel over such long
distances implies that pollutants emitted in one European country can
affect PM concentration in neighboring countries and even countries far
distant from the source.
• The chemical complexity and labile nature of atmospheric particulate
matter strongly favor real-time instrumental analysis techniques that
characterize pertinent physical and chemical properties without having to
collect, store, and transport samples. Real-time instruments that
characterize the chemical composition of atmospheric PM, ideally as a
function of particle size, are a more recent development.
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The aim of this study was to investigate and provide insights
into the sources and characteristics of submicron aerosols
through analysis of their size distribution, the temporal
variations of submicron particle compositions, and the
estimation of air mass transport.
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o
o
Preila 55 55’N; 21 00’E
Fig.1. Geographycal location of the station.
Sector 1 represent air masses from
the North Atlantic Ocean, the
Norwegian sea and Scandinavia,
supposedly, a clean sector, were
sector 3 (East Europe) and 5
(Western and Southern Europe) were
initially classified as polluted sectors
characterized different types of
pollution. Buffer sectors help to
separate different regions since it
was often impossible to attribute air
mass to solely one of major sector. 4
The AMS, developed by Aerodyne Research Inc., provides on-line quantitative
measurements of the chemical composition and size distributions of the nonrefractory fraction of submicron aerosol particles (approximately PM1.0).
Fig. 2. Aerosol mass spectrometer scheme
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Quantitative particle collection
efficiency (about 100%) in the
range of 60 to 600nm in diameter.
Collection extends to particles
about a factor of 2-3 smaller and
larger with reduced efficiency.
b)
Table 1. Main ion fragments used to identify inorganic and
organic aerosol species in AMS spectra.
The AMS does not characterize
individual organic molecules in
ambient air. This technique
quantifies two types of organic
aerosols, hydrocarbon-like and
oxygenated (HOA and OOA,
respectively), which together
account for almost all the
organic aerosol mass measured
by the AMS.
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Fig. 3. Mass concentration (μg·m-3) of nitrate, sulfate, ammonium, organic compounds, and total
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aerosol mass.
North Atlantic air masses
100
Organics
Sulfate
5%
80
Percent %
16%
Chloride
Sulfate
Nitrate
Ammonium
Organic
60
7%
40
60%
12%
South Europe air masses
20
Sulfate
Nitrate
Ammonium
Organic
4
09
-1
3
09
-1
20
06
-
2
20
06
-
1
09
-1
20
06
-
0
09
-1
20
06
-
9
09
-1
09
-0
20
06
-
8
09
-0
20
06
-
7
09
-0
20
06
-
6
09
-0
20
06
-
5
20
06
-
09
-0
20
06
-
20
06
-
09
-0
4
0
35%
Date
47%
Fig. 5. Mass fraction of sulfate and organic
compounds to the total aerosol mass concentration
measured by AMS at Preila.
5%
13%
b)
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R2 = 0.83
Sulfate, g m
-3
6
5
4
3
2
1
0
0.0
1.0
2.0
3.0
4.0
Organic compounds,g m
5.0
6.0
-3
Fig. 6. Correlation between sulfate and organic compounds: a) in clean air mass; b) in
polluted air mass.
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25
RH
95
90
20
85
15
80
10
75
70
5
65
60
0
550
Mode, nm
t
Size distribution m ode
450
350
Org
250
SO4
NO3
150
50
1
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Concentration, g m
-3
14
12
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NO3
SO4
Org
PM 1
16
21
10
8
6
4
2
Date
Fig. 8. Time series of nitrate, sulfate, and organic
mass concentration for the whole campaign,
together with time series of the mode diameter of
these species.
9/15/2006 4:30
9/14/2006 4:30
9/14/2006 16:30
9/13/2006 16:30
9/13/2006 4:30
9/12/2006 16:30
9/12/2006 4:30
9/11/2006 4:30
9/11/2006 16:30
9/10/2006 4:30
9/10/2006 16:30
9/9/2006 4:30
9/9/2006 16:30
9/8/2006 16:30
9/8/2006 4:30
9/7/2006 16:30
9/7/2006 4:30
9/6/2006 4:30
9/6/2006 16:30
9/5/2006 4:30
9/5/2006 16:30
9/4/2006 4:30
9/4/2006 16:30
0
Temperature, oC
Relative humidity, %
100
Comparison of the time series of
modes of the size distributions of the
individual species and their mass
concentrations shows a significant
relationship
between
these
quantities.
Based on results from the
mass concentration measurements,
the pollution events are primarily
related to regional transport rather
than to intense local production. This
suggests that the aerosol observed
during these events is dominated by
aged aerosol that has been
transported to the site and is
consistent with the observed larger
mode diameter size distributions.
During times of low total mass
concentrations, the locally produced
fraction of young and small particles
play a larger role in the aerosol size
distribution, shifting the mode
diameter to smaller sizes.
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Data points
Lognormal distr.
Data point
Org
70
60
50
40
30
20
10
0
dM/dlogD p , g m-3
dM/dlogD p, g m-3
10
8
6
4
2
0
10
100
Data points
Dp, nm
1000
10000
100
Data points
dM/dlogD p , g m-3
dM/dlogD p , g m-3
10
Dp, nm 1000
10000
Lognormal ditr.
120
SO4
2.5
Org
Lognormal distr.
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Lognormas distribution
SO4
100
2
1.5
1
0.5
0
80
60
40
20
0
10
100
Dp, nm
1000
10000
10
100
Dp, nm 1000
10000
Fig. 9. Size distribution of sulfate and organic aerosol fractions: a) in air mass from the North
Atlantic Ocean; b) in air mass from Southern Europe
10
100
a)
18
44
P re ila
N o rth A tla n tic a ir m a s s
90
80
43
70
60
50
40
27
30
29
P re ila
S o u th e rn E u ro p e a ir m a s s
90
R elative intensity
R elative intensity
80
44
18
100
58
55
41
20
6769
10
79 83
70
43
60
50
29
40
27
30
41
55
20
91
10
0
10
20
30
40
50
m /z
60
70
80
90
100
0
10
20
30
40
50
60
70
80
90
100
m /z
The derived mass spectrum demonstrates close similarity in the overall pattern with those
of aged/oxidized organic aerosols in rural areas.
The mass spectrum obtained in a comparatively clean period is similar to that obtained in a
polluted period but differs in a number of ways.
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Conclusions:
• The major observed components of the aerosol particles (PM1) were sulfate
and organic compounds. Large contribution of organic matter was
established in all air masses, and it reached 60 % of the total aerosol
particle mass in the clear Atlantic air masses.
• The size distribution of sulfate-containing particles and organic-containing
particles in the accumulation mode differed in shape and had a mode
diameter of about 340 nm and 190 nm, respectively. This difference implies
that species were externally mixed. In polluted air masses the size
distribution of sulfate-containing particles and organic-containing particles
was similar, the modal peaks of the sulfate and organic compounds were
equal, showing that chemical species were internally mixed.
• Dominant mass fragments m/z = 44 coupled with m/z 18 in the organic
fraction indicate that aerosol is aged. The mass spectra of the organic
fraction in clean and polluted periods show different fragmentation. These
changes may well reflect the change in the source.
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Take home messages
•
•
•
Ratios of CO to EC are used to determine the influences of anthropogenic
activity on aerosol composition. Low OC/EC ratios indicate anthropogenic
influences on aerosol composition due to the larger fraction of combustion
derived elemental carbon.
More than 50% of organic compounds of the total aerosol mass was found in the
fine aerosol fraction, while 23–44% was in the coarse particles. This difference
can be explain by difference particles formation mechanisms.
The size distribution of hydrocarbon-like aerosol (HOA) shows a distinct
ultrafine mode that is commonly associated with fresh emissions while
oxygenated organic aerosol (OOA) is generally concentrated in the accumulation
mode. These observations suggest that HOA is likely primary aerosol from local,
combustion-related emissions and that OOA is secondary organic aerosol (SOA)
influenced by regional contributions.
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