Brown carbon in the continental troposphere: sources, evolution and radiative impacts Evolution of...
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- Slide 1
- Brown carbon in the continental troposphere: sources, evolution
and radiative impacts Evolution of Brown Carbon in Wildfire Plumes
-Submitted to GRL- Rodney Weber, Haviland Forrister, Jiumeng Liu,
Athanasios Nenes, Eric Scheuer, Jack Dibb Luke Ziemba, Kenneth L.
Thornhill, Bruce Anderson, Glenn Diskin Anne Perring, Joshua
Schwarz Pedro Campuzano-Jost, Jose-Luis Jimenez Georgia Tech,
University of New Hampshire, NASA Langley, NOAA, University of
Colorado
- Slide 2
- BrC Background Biomass burning emissions projected to increase.
Contribution likely underestimated, (tracers lost). Biomass burning
is a major source of BrC. BrC is ubiquitous (if use a direct
measurement). BrC makes non-negligible contribution to TOA
radiative forcing (DC3 results, Liu et al, GRL 2014) Studies
suggest BrC can be predicted from BC/OA emissions (Saleh et al.,
Nature GeoSci 2014), application to models. Recent chamber
experiments show BrC is not stable (bleaches) (Lee ES&T 2014,
Zhao ACPD 2015). Goal: Investigate stability of BrC in ambient
smoke plumes. Focus on Rim 1 and Rim 2 fires, uniquely large
t.
- Slide 3
- Measuring BrC in Aerosol Extracts UV-Vis Light source
Spectrophotometer detector Sample inlet Sample outlet 2.5 m wave
guide Dissolved Species Why measure BrC in solutions ? Isolate BrC
from other light absorbers (BC, mineral dust) Long path wave guide
high sensitivity Insights in to BrC sources, chem., evolution X
Loss of aerosol optical effects (particle size, mixing state)
Filter SEAC4RS Approach: BrC = water then methanol extract
(series), Here focus on total (water+methanol) light absorption at
365 nm Abs(365nm) measuring chromophore concentrations UNH filters,
300 to 600 nm
- Slide 4
- SEAC4RS Biomass Burning Events: Rim 1 and 2 Wildfires Tracked
over large region
- Slide 5
- Investigating Plume Evolution All data merged to filter
sampling times. Account for dilution with Normalized Excess Mixing
Ratios wrt CO ( BrC/ CO), Plume transport time estimated from
HYSPLIT back trajectories. Close to fire, contributions from
different fires? As expected: Not much change in BC relative to CO
with plume age. Now look at BrC Time from Idaho fires Time from
Yosemite fires 1 st test with BC
- Slide 6
- BrC Evolution in Rim Fires: BrC Decreases with Plume Age
relative to CO Most of RIM fire biomass- burning BrC is not stable.
Half-life approx. 9 to 15 hours. Cause: bleaching, BrC is semi-
volatile ? Transport time assuming two separate fires All times
back to Yosemite fire life ~ 9 hrs from exp fit life ~ 15 hrs
- Slide 7
- BrC Evolution in Rim Fires: Decreases during periods of sun
exposure Photo-bleaching ? Transport time assuming two separate
fires All times back to Yosemite fire
- Slide 8
- Trends in AAE, BC coating thickness, OA/ CO, O:C Ratio and f60
AAE also decreases, somewhat similar trend as BrC. BC coating has
no trend BrC is driving AAE not optics of shell/cores Different
trend in BrC loss and OA BrC chromophores are small mass fraction
of OA BrC and O:C ratio have opposite, but similar trends BrC and
f60 similar trends
- Slide 9
- Trends in BrC/ CO vs AAE and f60 for Rim and other fires
- Slide 10
- BrC decreases with smoke age relative to CO, but some fraction
remains Transport time assuming two separate fires BrC: in plume /
bkg) ~ 6 Some fraction of the BrC is stable; a possible source of
the background tropospheric BrC ?
- Slide 11
- DC3: Observed Throughout Background Free BC BrC Total Inferred
from PSAP Altitude, km BrC/BC Observed BrC is ~ 20% of direct
radiative forcing Liu et al, GRL 2014 @365nm Surface albedo, gases,
altitude-resolved aerosols, T, BC Only -25 W/m 2 BC + BrC -19 W/m 2
TOA Instantaneous Forcing 13 km 0 km Radiative transfer model:
SBDART Is this stable smoke BrC?
- Slide 12
- Results 1.BrC prevalent in biomass burning plumes, but most is
unstable with half-life of 9 15 hrs (bleaching, semi-volatile BrC
loss, ?). 2.Fresh smoke BrC is dynamic, but a stable fraction
exists and may be source of observed ubiquitous background BrC that
is optically important. 3.Cant predict BrC solely on emissions.
Changes with aging appear complex. Smoke has multiple environmental
impacts. 1.Climate (BrC) 2.Visibility (BrC) 3.Linked to adverse
health impacts (BrC is well correlated with measures of aerosol
toxicity, Verma and Weber et al., 2014, 2015).