Recent advances in understanding the characteristics, impacts, and fate of biomass burning emissions Sonia M. Kreidenweis Professor Department of Atmospheric Science AP Photo/Ed Andrieski Second SINO-US Workshop on The Challenges Ahead: Sustainability Issues at the NEWCAP 8-9 September 2014

Fires around the globe (2010)

Biomass burning impacts surface dimming solar heating possible ice nuclei affect cloud albedo Direct impact on climate through light scattering and absorption decrease snow/ice albedo reduce cloudiness due to dynamical response to heating Above are for EMITTED PARTICULATE MATTER… effects on tropospheric gas-phase chemistry also expected affect precipitation?

Burning in North America (Image: from van der Werf et al., ACP, 2006) In the U.S., about 2 million acres per year of federal forests were burned by prescribed fires from 1998 to 2006, in comparison to around 6 million acres of wildfires (Tian et al., ES&T, 2008)

From a presentation by Running & Reinhardt, Fires projected to increase Already on rise due to many years of fire suppression policies in US  Pressure to conduct prescribed burns, with resulting impacts on air quality

Agricultural burning in US “average interannual variability of crop residue burning emissions of +/- 10%” (McCarty, JAWMA, 2011)

Examples of crop burning (AR, CA, FL, ID TX, WA), McCarty et al., SciTotEnv, 2009

Lab studies (FLAME I - IV) USFS / USDA Fire Sciences Laboratory, Missoula, MT Emission factors Optical properties Cloud-interaction potential

Examples of fuels studied

“soot” organic matter Composition of particles in the lab studies (Levin et al., JGR, 2010)

“soot” organic matter Composition of particles in the lab studies Al, Ca largest contributors to “ash” elements Some fuels produced surprisingly large mass fractions of INORGANIC species Potassium salts most common Two fuels had large chloride emissions

organic matter Composition of particles in the lab studies Al, Ca largest contributors to “ash” elements Some fuels produced surprisingly large mass fractions of INORGANIC species Potassium salts most common Two fuels had large chloride emissions

SMOLDERINGFLAMING “Soot” content depends on efficiency of combustion Fraction of particulate matter that is “black carbon” (McMeeking et al., JGR, 2009)

Single-scattering albedos (McMeeking et al., JGR, accepted) Modified combustion efficiencyBlack carbon fraction of aerosol mass More BC  more absorbing (AND depends on fuel)

Single-scattering albedos (McMeeking et al., JGR, accepted) Modified combustion efficiencyBlack carbon fraction of aerosol mass More BC  more absorbing (AND depends on fuel) More efficient  more BC (AND depends on fuel)

“Brown” carbon Processing temperature increases  405 nm: strong reduction in light absorption with heating 532 nm781 nm

Absorption Ångström exponents Very “black” smoke: closer to diesel soot (absorbs over all λs) “bright” smoke: highly reflective in vis, absorbs strongly at shortλs (McMeeking et al., JGR, submitted)

Absorption Ångström exponents Very “black” smoke: closer to diesel soot (absorbs over all λs) “bright” smoke: highly reflective in vis, absorbs strongly at shortλs Highlights contrasts between fossil fuel derived black carbon and light-absorbing aerosol from biomass burning

Brown and black carbon in fog from China Fogwater samples from Taishan obtained in CSU collaborative study with Shandong U and Hong Kong Polytechnic; image courtesy Prof. Jeff Collett

Brown and black carbon in fog from China Fogwater samples from Taishan obtained in CSU collaborative study with Shandong U and Hong Kong Polytechnic; image courtesy Prof. Jeff Collett SOA, “brown carbon” Lim et al., 2010 Boris et al., 2014

Colorado fire season: Regional smoke resulted in highest AOD

What are the semivolatile components? Increasing vapor pressure 

What are the semivolatile components? Increasing vapor pressure  particles gases

What are the semivolatile components? Increasing vapor pressure  particles gases Either phase

Controlled dilution studies

The majority of initial “particulate” ends up in gas phase after dilution Large variability in EF ~50% of PM mass is lost in dilution to ~100 µg m -3 Further evaporation below ~100 µg m -3 ? normalized mass fraction remaining [Levin, May et al., in preparation]

What is the fate of these evolved gases? CMU smog chamber

New aerosol mass formed (sometimes…) Hennigan et al., ACP, 2011

Loss of organic aerosol downwind in plume May et al., in prep [OA] plume [CO] plume Aircraft data, Ft. Jackson burn

Loss of organic aerosol downwind in plume May et al., in prep [OA] plume [CO] plume Aircraft data, Ft. Jackson burn Aerosol was becoming more oxidized (SOA production?), but loss dominated

Conceptual picture new particle formation OZONE FORMATION Secondary pollutants Primary pollutants

Fire’s influence on photochemistry VOCs NOx O 3 PAN

Ozone enhancement from biomass burning? Jaffe and Wigder (2012): Ozone production from wildfires: A critical review  estimate global wildfires produce approximately 3.5% of all global tropospheric O 3 production  In plumes: observed  O 3 /  CO range: -0.1 to 0.9  Interactions of numerous factors including  fire emissions,  efficiency of combustion,  chemical and photochemical reactions, and age,  aerosol effects on chemistry and radiation, and  local and downwind meteorological patterns

Summary  Biomass burning is ubiquitous, and increasing globally  wildfires highly variable, agric burning more consistent  We are just beginning to understand what constitutes the semi-volatile organic emissions, how they react in the atmosphere, and their role in secondary organic aerosol formation  Biomass burning likely plays a role in N deposition budget  The chemistry of the aqueous phase is likely important, but work on this just beginning  More controlled lab studies needed, plus field work  provide data needed by modelers!