Theme 1: Carbonaceous Aerosol (EC and OC)
• Theme Leader: Abbatt, UofT (POLAR6, Amundsen, Alert, snow
measurements); Co-Leader: Leaitch, EC (POLAR6,Whistler, Alert
measurements, optical properties)
• Co-investigators: Bertram, UBC (Whistler, Alert measurements),
Evans, UofT (snow measurements, source-receptor analysis, optical
properties), Jia, UofT (modeling), von Salzen, EC, UVic (modeling),
Martin, Dal (modeling)
• Collaborators: Cziczo, MIT (PCVI and residual analysis expertise),
Huang, EC (EC/OC, carbon isotope measurements), Li , EC (SP2;
aerosol chemistry), Liu, EC (particle measurement), Macdonald, EC
(Whistler measurements, CVI expertise), Russell, Scripps
(STXM/FTIR measurements of filter samples), Sharma EC(Arctic,
snow measurements), Staebler, EC (Arctic air quality
measurements), Law/Thomas LATMOS, France (modeling), Herber,
AWI (measurements), Schneider, MPI (measurements)
Why Black Carbon (BC)?
•
•
•
•
•
•
Relative to OC, BC in remote regions, particularly the Arctic, is well studied.
However, there remain many unknowns concerning BC, and the ability of
models to represent BC for climate and mitigation is at best poor.
BC aerosol directly warms the atmosphere by absorption of solar radiation.
Bond et al. (2013) estimate global direct radiative forcing of BC from
industrial sources at +0.71 W/m2 with 90% bounds of +0.08 and +1.27
W/m2.
Light absorption by BC deposited to snow or ice surfaces enhances melting
of the snow or ice surface (e.g. McConnell et al., 2007; Bond et al., 2013).
The degree of scavenging of particles containing BC by clouds and its
deposition to the Arctic ice and snow is poorly constrained in models,
despite predictions of BC loadings being highly sensitive to this parameter
[Koch et al., 2009].
As a primary emission of incomplete combustion (anthropogenic and
biomass burning), BC may play a fundamental role in defining the aerosol
size distribution, which means that it also possesses atmospheric cooling
potential (e.g. Chen et al., 2010).
For one discussion of terminology, see Petzold et al., Atmos. Chem. Phys., 13, 8365–8379, 2013.
From A. Stohl et al., Atmos.
Chem. Phys., 13, 8833-8855, 2013
Fossil and biofuel BC emissions (ng/m2/s) for 2008; from Sand, M. et al.
Arctic surface temperature change to emissions of black carbon within
Arctic or midlatitudes, JGR-Atm., 2013.
Quinn et al., AMAP, 2011
BC in the Arctic
Representative modelling of transport
within and above the Arctic dome is
critical. (JB)
Stohl et al model
Alert Time Series
Stohl et al model from Stohl et al.,
Atmos. Chem. Phys., 13, 8833-8855,
2013; Alert observations are 20082010 and based on PSAP using a
MAC of 10.
EC and OC from 2005-2010; rBC is
from 2011-2012 (from Leaitch et al.,
Elementa, 2013). OC/EC is about 3
during haze period and 6 in the
summer.
Alert observations
16
0.14
EC
OC
rBC number
0.12
14
12
0.10
10
0.08
8
0.06
6
0.04
4
0.02
2
0.00
0
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Month
rBC Number concentration (cm-3)
The comparison of the simulations and the
observations in this case indicate
reasonable prediction for the surface. The
discrepancy between the observations and
the model in Stohl et al among other things
indicates the importance of understanding
the differences among the various
techniques used to measure or estimate
BC (Quinn and Bates, JGR, 2005; Bond et
al., 2013). But the models aren’t perfect
either…
Filter mass concentration (g m-3)
0.16
Profiles
Approx 26 profiles
From Sharma et al., JGR-Atm., 118, 2013
for 1990-2005 (flaring emissions?).
From Stohl et al., Atmos. Chem.
Phys., 13, 8833-8855, 2013
Despite reasonable agreement between the model and the observations
near the surface, the observations suggest a larger BC burden than
predicted by Stohl et al. Overall the numbers of observations are too
limited to draw a conclusion, except that more profile observations and
model comparisons are important.
BC Size Distribution – does it matter?
BC is often viewed in isolation from other aerosol
components. Understanding the BC and how it affects
climate requires more knowledge (and predictive
capability) of its size distribution and its interaction with
other components of the aerosol in remote regions of the
globe.
•
•
The MAC coefficient that
is used to convert light
absorption to BC mass is
strongly dependent on
the size of BC and how it
is combined with other
aerosol components.
The degree of coating,
the morphology of the BC
inclusion(s) and the size
of the BC inclusions
control the effectiveness
of BC as a warming
agent. (SH)
Quinn et al., AMAP, 2011
BC probable
BC unlikely?
BC possible
From Bond et
al., JGR, 2013
–
Effect of dust
deposition on
BC deposition
Why Organic Carbon (OC)?
• OC results from secondary production (oxidation of VOCs from biogenic, BB
and anthropogenic sources) as well primary emissions (anthropogenic and
biomass burning). Natural sources, such as biogenic emissions of terpenes,
are significant sources of OC.
• OC plays a fundamental role in defining the aerosol size distribution, due to
primary emissions and also due to secondary processes involving organic
components affecting nucleation (Almeida et al., Nature, 2013) and growth
rates of Aitken particles (Riipinen et al., ACP, 2011).
• Studies of OC in remote regions, particularly the Arctic, are few. At Alert, OC
from biogenic VOC oxidation has been identified (specifically isoprene) in
early June by Fu et al. (EST, 2009), a result that is consistent with the higher
OC/EC value measured at Alert during summer. VOCs will also result from
biomass burning and, during the Arctic Haze period, various anthropogenic
sources including flaring.
• Light absorption by OC, or brown carbon, happens at lower visible
wavelengths. Mass absorption by brown carbon for biomass burning plumes
transported into the Arctic can be significant at blue wavelengths
(McNaughton et al., ACP, 2011).
NETCARE’s Carbonaceous Aerosol Questions
•
•
•
•
•
•
What is the relative importance of the mechanisms for BC and OC
deposition to Arctic snow and ice, and what evidence is there for deposition
in the boundary layer or via ice clouds? Does BC influence ice clouds
(Coupled with Theme 2), which may enhance the deposition?
What is the vertical distribution of BC and OC in the Arctic atmosphere?
Can we clearly identify source regions for EC and OC?
What are the levels and sources of BC and OC, including brown carbon, in
snow? What are the implications of carbonaceous loadings in snow for
radiative forcing?
How do BC and OC loadings from biomass burning compare with
anthropogenic BC and OC over the Arctic and Western Canada? Will an
increase in boreal forest fires in a warmer climate may lead to more black
carbon transport to remote regions.
Can we predict the observed optical properties of the aerosol in remote
Canada? (Coupled to theme 4)
What would be the consequences of reducing or eliminating BC? (Coupled
to theme 4)
BC and OC Activity Overview
New ambient measurements of BC and OC
•
New observations will be made of BC and OC
loadings, mixing state, size distributions, cloudnucleating properties, and optical properties.
•
The observations will cover a large range of
environments from the ground to the free
troposphere at the sites shown to the left; the
Lancaster Sound measurements will be from the
CCGS Amundsen.
•
Two intensive sets of measurements using the AWI
POLAR 6 aircraft will be conducted: in summer
2014 from Resolute in coordination with the
Amundsen, and in spring 2015 PAMARCMIP style
(including Alert and Resolute).
•
Together with model simulations (Theme 4) and
source-receptor analysis, these observations will
be used to:
–
–
–
–
improve the BC and OC source contributions,;
examine the single scattering albedo (SSA) and the
potential influence of coatings on the SSA;
Study the contribution from carbonaceous aerosol to
absorption in the atmospheric column relative to
absorption from surface deposition.
understand the balance between warming from
absorption by BC and brown carbon versus the
cooling influence from the effects of BC and OC on
the aerosol size distribution.
NETCARE Plans for OC and BC
•
Ground-based and airborne measurements at Resolute and Alert will be used to
characterize the Arctic Haze phenomenon, Asian trans-oceanic pollution transport,
biomass burning plumes, potential sources of particles from the marginal ice zone
and the short-term evolution of ship emissions. The spring measurements will also
measure ice crystals to look for associated changes in BC.
•
The new Whistler high elevation site measurements will be used to characterize
aerosols from biomass burning and long range transport from Asia and to assess
their impacts. We will determine background levels and optical properties of
carbonaceous aerosol, as well as the impact of long range transport from Asia to
Western North America upon this background. Source apportionment techniques will
be applied to measurements of aerosol particles reaching the Whistler and Alert sites.
•
A focused campaign at Alert will conduct measurements downstream of a groundbased counter flow virtual impactor (CVI) to measure the scavenging fraction of BC
and OC as a function of size for ice particles.
•
BC and OC loadings, including brown carbon, in snow at remote sites will be
quantified to enable better estimates of the warming from reduced snow albedo.
Source receptor-modeling will be applied to the snow constituents to provide
information about the sources of BC and BB.