Natural aerosols: Global budgets and climate implications Aerodyne, Inc. April 10, 2009 Colette L. Heald
CLIMATE SENSITIVITY: HOW AEROSOLS CAN MESS UP A NICE SIMPLE PICTURE ΔTΔT ΔCO 2 Climate Sensitivity is ΔT for ΔCO 2 but CO 2 is not the only thing changing! Which makes THIS very difficult for GCMs to predict (i.e. is climate sensitivity really a useful concept?) ΔSO 4
OR IN OTHER WORDS… BUT, What were 1750 conditions? A thorn in the side of the O 3 community: Preindustrial ozone models } Observations at mountain sites in Europe [Marenco et al., 1994] Can safely assume that PI continental sulfate/BC ≈ 0 What about the ‘natural’ radiative effect?
WHY WE SHOULD BE CONCERNED ABOUT NATURAL AEROSOL LOADING QUESTION 1: Are we missing an important contributor to the Earth’s radiative balance? If so, how much is there? What controls production/processing in the atmosphere? Can we predict how this loading will change? QUESTION 2: What were pre-industrial concentrations of these “natural” aerosols? Today, I’m going to focus on organic aerosol, with the perspective on global budgets and future predictions Pre-industrial aerosol number CRITICAL for estimate of indirect effect July 97 [Spracklen et al., 2005]Pre-industrial values?
DISTURBANCE: Fires, beetles, land use change EMISSIONS: Particles Organics NOx … + oxidants + oxidation O3O3 ANTHROPOGENIC INFLUENCE ↓ OH = ↑ CH 4 lifetime + FEEDBACKS FROM CLIMATE CHANGE (moisture, precipitation, T, hv) ? PBAP SOA C5H8C5H8
SECONDARY ORGANIC AEROSOL: MORE THAN WE THINK? ITCT-2K4 IMPEX AMAZE-08 AMMA Models aren’t necessarily getting it right for the right reason. SOA production perhaps not quite so dominant as suggested by earlier studies? Key question: natural or anthropogenic? Must break down at point where signatures diluted/removed Current model estimates of SOA production: Tg/yr
FUTURE PREDICTION OF SECONDARY ORGANIC AEROSOL Sources may be large(?), how MIGHT they change? ZONAL MEAN SOA CONCENTRATIONS: (ANTHROPOGENIC EMISSIONS): POA (partitioning) Aromatics (precursor) Trace gases (NOx, oxidants) (BIOGENIC EMISSIONS): BVOC (precursor) (CLIMATE): Precipitation (lifetime) T (partitioning, oxidation) Convection (distribution, lifetime) Lightning (NOx aloft) Water vapour (P OH ) (ANTHROPOGENIC LAND USE) Climate impact is complex/compensatory/uncertain. Predict large increase in SOA burden (> 20%) tied to T-driven BVOC emissions, with large sensitivity to future land use. Global Model: NCAR CAM3-CLM3 (2 x2.5 ) [Heald et al., 2008]
METEOROLOGICAL AND PHENOLOGICAL VARIABLES CONTROLLING ISOPRENE EMISSION LIGHT Diffuse and direct radiation Instantaneous and accumulated (24 hrs and 10 days) TEMPERATURE (Leaf-level) instantaneous and accumulated (24 hrs, 10 days) T PAR LL TT [Guenther et al., 2006] SOIL MOISTURE suppressed under drought AMOUNT OF VEGETATION Leaf area index (LAI) Month LAI SUMMER LEAF AGE Max emission = mature Zero emission = new E isoprene ≈ E CH4
ISOPRENE IN THE FUTURE Isoprene emissions projected to increase substantially due to warmer climate and increasing vegetation density. LARGE impact on oxidant chemistry and climate NPP ↑ Temperature↑ Surface O 3 ↑ ppb [Sanderson et al., 2003] Methane lifetime increases [Shindell et al., 2007] SOA burden ↑ > 20% [Heald et al., 2008]
CO 2 INHIBITION COMPENSATES FOR PREDICTED TEMPERATURE-DRIVEN INCREASE IN ISOPRENE EMISSION CONCLUSION: Isoprene emission predicted to remain ~constant Important implications for oxidative environment of the troposphere… * With fixed vegetation E isop (TgCyr -1 ) (A1B) MEGAN MEGAN with CO 2 inhibition Global Model: NCAR CAM3-CLM3 (2 x2.5 ) Empirical parameterization from plant studies [Wilkinson et al., GCB, in press]
UNLESS…CO 2 FERTILIZATION IS STRONG CLM DGVM projects a 3x increase in LAI associated with NPP and a northward expansion of vegetation. [Alo and Wang, 2008] Isoprene emissions more than double! (1242 TgCyr -1 ) BUT, recent work suggests that NPP increases may be overestimated by 74% when neglecting the role of nutrient limitation [Thornton et al., 2007] [Heald et al., GCB, in press]
PREDICTED CHANGES IN VEGETATION FROM 8 GCM’S Same land model (CLM) driven by 8 different climate projections Very sensitive to precip [Alo and Wang, 2008] LAI ( ) [mm] Future land use may be the greatest uncertainty in climate (and chemistry!) predictions
AND I HAVEN’T EVEN MENTIONED THESE… Pictures courtesy: Nick Hewitt, Christine Wiedinmyer Deforestation in Rondonia Boreal wildfires Pine beetle kill in the Rocky MountainsPalm Plantations in Malaysia
IMPLICATIONS FOR THE PAST? VOSTOK ICE CORE RECORD While the balance between T and CO 2 is critical to future predictions of isoprene, the large T fluctuations over the last 400 thousand year remain the primary control on isoprene emission in the recent geological past. However effect at low CO 2 highly uncertain Vostok data source: Petit et al. [1999] LGM
PRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP) POLLEN BACTERIA VIRUSES FUNGUS ALGAE PLANT DEBRIS Jaenicke [2005] suggests may be as large a source as dust/sea salt (1000s Tg/yr) Elbert et al. [2007] suggest emission of fungal spores ~ 50 Tg/yr
CURRENT SOURCE ESTIMATES FOR ORGANIC AEROSOL (Tg/yr) WITHOUT PBAPWITH PBAP? PBAP estimates ~1000 Tg/yr would swamp all other sources of organic aerosol. Fungal spores emissions equivalent to biomass burning? Budget #’s from GEOS-Chem [Park et al., 2003; Henze et al., 2008]
PBAP ACROSS THE SIZE RANGE? From Andi Andreae (unpublished data) Dominates the coarse mode (pollens, debris…) May also make important contribution to fine mode aerosol PM2.5
MANNITOL: A UNIQUE TRACER FOR FUNGAL SPORES 1 spore contains 1.7 pg mannitol [Elbert et al., 2007; Bauer et al., 2008] Organic matter: 33 pg/spore [Bauer et al., 2008] OR 65 pg/spore [Elbert et al., 2008] CONVERSION: [OM] = 38[mannitol] Average sugar alcohol content at different sites in Vienna Comparing measured mannitol w/ concentrations estimated from spore counts [Elbert et al., 2007] [Bauer et al., 2008]
If we implement this constant emission in a model, how does it fare? What about size ranges? Mannitol concentrations in fine aerosol (PM 2.5 ) were ~3-4 times less than in coarse mode assume 20% of emission as fine FUNGAL SOURCE ESTIMATED BY ELBERT ET AL., 2007 Compiled mannitol concentrations measured in various seasons/locations. Took extratropical concentration (25 ng/m 3 ) as “typical” and estimated emissions as 50 Tg/yr (OR1.1 g m -2 s -1 ). PBAP OA (PM2.5) (unsurprisingly?) Doesn’t capture the seasonal/geographical variability in the observations. Summer Fall Winter
WHAT DRIVES MANNITOL/FUNGAL SPORE EMISSION? Potential meteorological/phenological drivers [Jones and Harrison, 2004]: Temperature, radiation, wind speeds,surface wetness, precipitation, leaf area index (LAI), RH, water vapour concentrations and boundary layer depths BEST drivers are LAI and water vapour concentrations. CAUTION: not necessarily causal!
GEOS-CHEM SIMULATION OF FUNGAL SPORE PBAP WITH OPTIMIZED EMISSIONS Constant Emission Optimized Emission = f(LAI, H 2 O) VAST improvement for fine PBAP: capture variability, unbiased simulation MODEST improvement for coarse PBAP: relatively unbiased, but other drivers? EMISSION = 7 Tg/yr (fine), 21 Tg/yr (coarse)
WHERE ARE FUNGAL SPORES AN IMPORTANT SOURCE OF ORGANIC AEROSOL? Generally contribute ~10% to fine mode surface OA, but > 30% in tropics
WHEN ARE FUNGAL SPORES AN IMPORTANT SOURCE OF ORGANIC AEROSOL? Pronounced seasonality in extratropics (corresponding to vegetation cover), peaking in late- summer/fall as in measurements. Taiwan Hyytiala [Sousa et al., 2008] [Ho et al., 2005] unpublished data, Hanna Manninen Porto, Portugal GEOS-Chem simulation
PBAP CONCLUSIONS Next up: implications for CCN (using GLOMAP model…) Fungal spores make a modest, but regionally important contribution to organic carbon aerosol budget. More observations needed to test… What about other PBAP types? FINE OA SOURCES COARSE OA SOURCE (Tg yr -1 ) [Heald and Spracklen, GRL, in press]
ANY INDICATION OF PBAP IN AMAZE-08? PRELIMINARY AMS obs: Scot Martin, Qi Chen (Harvard). Jose Jimenez, Delphine Farmer (CU Boulder) SIMULATED OC Early Feb: Fire influence Field site: close to Manaus, Brazil (in Amazonia), Feb-Mar NEED: (1) more ambient measurements of mannitol/spores (2) Better time series of measurements to resolve diurnal cycle No obvious indication of an important sub-micron PBAP in the “pristine” Amazon… Our ~ 30% contribution (to PM 2.5 ) would be consistent with measurement/modeling uncertainty.
THE TROPICS: THE IDEAL “NATURAL” AEROSOL ENVIRONMENT MODIS (Terra) Aerosol Optical Depths (550 nm) AMAZE (Feb 2008, Amazon) OP3 (July 2008, Malaysia) AMS organic loadings at the surface similar in these environments: g/m 3 (c/o: Qi Chen, Niall Robinson) Are even remote forests truly isolated from other sources? Fires (even in the wet season!) Saharan dust Fires Jakarta (8M people) NASA 2010 field campaign
CALIPSO AEROSOL PROFILES IN THE TROPICS Just starting to delve into CALIPSO observations (extinction at 532 nm)…. AMAZE (March 2008, Amazon) OP3 (July 2008, Malaysia) Use vertical information on extinction (and possibly “color” ratio) to tell us more about aerosol composition, sources & transport
ACKNOWLEDGEMENTS Dominick Spracklen Mick Wilkinson, Russ Monson Clement Alo, Guiling Wang Alex Guenther Qi Chen, Scot Martin Delphine Farmer, Jose Jimenez