Physical and chemical properties of freshly emitted and ... · 1 Rosaria Erika Pileci1, Michele...
Transcript of Physical and chemical properties of freshly emitted and ... · 1 Rosaria Erika Pileci1, Michele...
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Rosaria Erika Pileci1, Michele Bertò1, Robin Modini1, Stefania Gilardoni2,
Matteo Rinaldi2, Douglas Orsini2, Angela Marinoni2, Martin Gysel1
1 Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland
2Institute of Atmospheric Science and Climate, Italian National Research Council (CNR-ISAC) via Gobetti 101, 40129 Bologna, Italy
PM2018 – Matera – 24/05/2018
Physical and chemical properties of freshly emitted and aged particles determined from mobile measurements in the Po Valley
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Introduction:
Mass Absorption Coefficient (MAC) of Black Carbon
MAC is a key parameter when estimating black carbon radiative forcing. Uncertainties in MAC
Uncertainties in radiative forcing Uncertainties in climate predictions
𝐌𝐀𝐂𝐁𝐂 [𝐦𝟐𝐠−𝟏] = 𝛃𝐚𝐛𝐬,𝐁𝐂 [𝐌𝐦−𝟏]
𝐦𝐁𝐂 [𝛍𝐠
𝐦𝟑]
Introduction:
MAC, experimental uncertainty and variability
(Zanatta et al., Atmos. Env., 2016)
MAC at European
background sites:
~10.0 𝐦𝟐𝐠−𝟏 (@ 637 nm)
𝐌𝐀𝐂 for freshly BC:
𝟕. 𝟓 ± 𝟏. 𝟐 𝐦𝟐𝐠−𝟏 (@ 550 nm)
6.5 𝐦𝟐𝐠−𝟏 (@ 637 nm, AAE = 1) (Bond & Bergstrom, Aerosol Science
and Technology, , 2006)
Part of MAC variability is due to
measurements uncertanties!
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MAC of internally mixed “coated
BC” increases by up to a factor
of ~2 compared to bare BC core.
Introduction:
MAC, link to BC physical quantities
• Mixing state
• Core sizes
• Morphology
• Refractive index
Aim of the work
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• Studying the difference in properties between
freshly emitted and aged particles
• Explain the MAC variability with variations in BC physical properties:
- BC mass size distribution; - Mixing state
aging
• Atmospheric aging processes lead to internally mixed BC
• With mobile and stationary measurements in different locations!
Mobile measurements with MOSQUITA (to investigate spatial variability)
Licor (CO2) ; O3
CAPS PMssa (780 nm) (Extinction and
scattering) --------------------------
MAAP (637 nm) --------------------------
PAX (870 nm) (Absorption and
scattering) -------------------------- AETHALOMETER 7𝛌
HR ToF
AMS
SP2 (rBC mass and
mass size distribution,
coating thickness)
CPC
UHSAS (Size
distribution)
Drives repeated
San Pietro Capofiume Rural background
Remote background Monte Cimone
Urban background
Highway
Freshly emitted particles
Rural background road
Aged particles
July 2017
12 trips
4.000 km
Results: Black carbon optical properties (Drives between Bologna and Milano)
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fresh traffic BC
aged BC Evidence that atmospheric
aging increases the MAC of BC.
Results: The Challenge of mobile absorption measurements
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MAAP signals very noisy when doing mobile measurements.
Does it introduce a systematic bias? Can we recover the data?
Mobile Stationary
Results: CAPS – a good promise
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Extremely good correlation between CAPS PMssa absorption and rBC mass from
the SP2 at a time resolution of 5 secs
But how accurate are the absolute values?
Results: PAX, a challenge lost
50
40
30
20
10
0
-10
-20
Ab
sorp
tion
co
eff
icie
nt
(1/M
m)
13:3013.07.2017
14:00 14:30 15:00 15:30 16:00 16:30 17:00 17:30 18:00 18:30 19:00
Date & Time
Bologna - Monte Cimone Absorption coefficient time serie - PAX drift problem
Unsuccessful measurements both mobile and stationary!
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Results: MAC spatio variability
𝑯𝒊𝒈𝒉𝒘𝒂𝒚 𝑩𝒐𝒍𝒐𝒈𝒏𝒂 𝑪𝒊𝒕𝒚 𝑺𝒂𝒏 𝑷𝒊𝒆𝒕𝒓𝒐
𝑪𝒂𝒑𝒐𝒇𝒊𝒖𝒎𝒆
(14.4 ± 0.5 − 14.6 ± 0.6)
(9.8 ± 0.1 − 16.2 ± 1.1)
(18.4 ± 0.4 − 26.5 ± 0.7)
(Bond & Bergstrom, Aerosol Science and Technology, 2006)
(Zanatta et al., Atmospheric Environment, 2016)
5.3 @ 780 nm, AAE = 1
8.2 @ 780 nm, AAE = 1
Mixing state: delay time method
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BC mass
Op
tica
l dia
me
ter
Thinly-to-moderately
coated Thickly coated
Results: MAC vs Fraction of thickly coated particles
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MAC [18.1 – 26.2] background sites 14% - 18 % thickly coated particles
MAC [9.8 – 16.2] traffic dominated sites 1% - 6% thickly coated particles
Results:
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𝑩𝒐𝒍𝒐𝒈𝒏𝒂 𝑪𝒊𝒕𝒚
120 𝑛𝑚 < max (𝐷𝐵𝐶 ) < 155 𝑛𝑚
𝑺𝒂𝒏 𝑷𝒊𝒆𝒕𝒓𝒐 𝑪𝒂𝒑𝒐𝒇𝒊𝒖𝒎𝒆
max (𝐷𝐵𝐶) ≃ 150 𝑛𝑚
BC mass size distributions
𝑯𝒊𝒈𝒉𝒘𝒂𝒚 max (𝐷𝐵𝐶) ≃ 110 𝑛𝑚
Conclusions
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Mobile absorption measurements are tricky. There are uncertainties and this
complicate the absolute value of MAC
Nevertheless there is clear evidence of MAC variation:
explained with difference in BC coating thickness
Future analysis
- Quantitave mixing state;
- Improve data analysis: determine best available absorption measurements!
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Acknowledgments