1. Organic Aerosol: Budgets, Beetles and Bewilderment Dalhousie University August 24, 2012 Colette L. Heald with contributions from Bonne Ford, Ashley Berg and Qi Chen With thanks to : many individuals for invaluable field and satellite measurements

2. THE DISPROPORTIONATE IMPACT OF PARTICULATE MATTER ON THE GLOBAL ENVIRONMENT Global premature deaths from environmental risk Global radiative forcing By 2030 PM surpasses unsafe water as the leading environmental cause of premature deaths. PM is the largest source of uncertainty in global radiative forcing. [OECD, 2012] [IPCC, 2007]

3. ORGANIC AEROSOL MAKES UP AN IMPORTANT/DOMINANT FRACTION OF OBSERVED AEROSOL Globally makes up 25-75% of total fine aerosol at the surface (ignoring dust here). Could become more even more important in the future with sulphate clean-up? [Zhang et al., 2007] Sulphate Organics

4. WHAT IS AN ORGANIC AEROSOL? (THE CHALLENGE OF CHEMICAL COMPLEXITY) Sulfuric acid always looks like this: Soot consists only of carbon (just in different configurations): H 2 SO 4 NO YES Composition is KNOWN and CONSTANT And also things like this Composition is largely UNKNOWN and VARIABLE. Each peak is an individual molecule (i.e. organic chemistry is crazy)

5. A LARGE MISSING SOURCE OF ORGANIC AEROSOL? Models are woefully inadequate. Could be up to 10x more OA in atmosphere than sulphate! Models drastically underestimate SOA from 4 campaigns [Volkamer et al., 2006] ACE-Asia (2001): 3 groups measured high OA off Asia. GEOS-Chem simulation factor of 10-100 too low [Heald et al., 2005] Goldstein and Galbally [2007] suggest that SOA source may be anywhere from 140-910 TgC/yr. Obs (Maria et al., 2003) GEOS-Chem

6. MY TALK TODAY Part 3: Bewildering aerosol in the Southeastern US Part 1: Constraints on the global budget of OA Part 2: Impacts of the pine beetle infestation

7. Despite lack of mechanistic understanding of OA formation/loss, we have made progress in the last couple of years by using multiple dimensions of ambient measurements to evaluate/probe models: 1.Mass [de Gouw et al., 2005; Heald et al., 2005; Volkamer et al., 2006, etc, etc.] 2.Correlation / variability [Heald et al., 2006; Carlton et al., 2008] 3.Spatial distribution [Heald et al., 2010] 4.Source signatures from mass spectra [Hodzic et al., 2009; Spracklen et al., 2011] 5.Vertical profile [Heald et al., 2005; 2006; 2011; Carlton et al., 2008] 6.Elemental composition [Murphy et al., 2011; Chen et al., in prep] AN UNDERCONSTRAINED PROBLEM THAT REQUIRES A TOP-DOWN APPROACH 910 47 Existing GEOS- Chem sources 140 Our satellite top-down estimate 150 Bottom-up estimate [Goldstein and Galbally, 2007] All units in TgCyr -1 Satellite-based estimate [Heald et al., 2010] AMS surface-based optimization [Spracklen et al., 2011] 82 24 POA (fixed) SOA (optimized)

8. EXPLORING THE VERTICAL DIMENSION * All AMS measurements, except ITCT-2K4 (PILS) and ACE-Asia (filters). 17 aircraft field campaigns (2001-2009) Aircraft constraints on the organic aerosol distribution through depth of troposphere in remote, polluted and fire influenced regions. GOAL: investigate vertical profile and compare with one CONSISTENT model. Measurements PIs: Hugh Coe (ITOP, ADRIEX, DABEX, DODO, AMMA, ADIENT, EUCAARI, OP3, VOCALS-UK, TROMPEX), Jose Jimenez, (MILAGRO, IMPEX, ARCTAS), R. Weber (ITCT-2K4), Ann Middlebrook (TexAQS), Lynn Russell (ACE-Asia) GEOS-Chem SOA simulation: 2 product model, monoterpenes/sesquiterpenes +OH/O3/NO3 (Griffin et al, 1999), low-NOx isoprene+OH (Kroll et al., 2006), NOx dependent aromatics +OH(Ng et al., 2007)  latest description Henze et al., 2008

9. COMPARISON OF VERTICAL PROFILE General profile: drops off with altitude, with BB plumes aloft. Over remote regions, little structure to profile. Outliers: AMMA, ACE-Asia. Model roughly captures profile. “Reasonable” assumption on profiles made in Heald et al. [2010] looking at satellite

10. CAN WE ATTRIBUTE THE MODEL UNDERESTIMATE? Adding ~100 Tg/yr source of ASOA (as suggested by Spracklen et al., 2011) improves comparison in polluted regions, but leads to too much OA aloft and in remote regions. OA sink? *ASOA = anthropogenically controlled SOA

11. A POSSIBLE ORGANIC AEROSOL SINK time Oxidation in atmosphere = ↓ volatility = more particle FUNCTIONALIZATION (Adding oxygen) FRAGMENTATION (Breaking into smaller molecules) Oxidation in atmosphere = ↓ volatility = ↑ volatility Acts like a “sink” of particles time Lots (too much?) particle formation mass For the first time, test the impact of this fragmentation “sink” in a model.

12. Estimate that gas-phase fragmentation can decrease global SOA burden by up to 50%. Heterogeneous oxidation impact less (16%). Adding ~100 Tg/yr of ASOA and a gas fragmentation sink brings model simulation to within 1  g/m 3 of observed concentrations in 15 of 17 campaigns. Model may need SOURCES and SINKS. ASOAx30 + fragmentation sink IMPACT OF ADDING BOTH SOURCES AND FRAGMENTATION SINK ON COMPARISONS WITH FIELD DATA [Heald et al., 2011] Baseline Gas-phase oxidation, k OH =2x10 -11 cm 3 /molecules/s Heterogeneous oxidation k OH =1x10 -12 cm 3 /molecules/s 5% lost to fragmentation

13. ADDING ANOTHER DIMENSION: THE OXYGEN CONTENT OF OA Qi Chen (MIT) Example of fitting 2 product elemental composition (isoprene +OH, low NOx) POABiogenic SOAAromatic SOA Estimated initial O:C from fitting/literature (for species in GEOS-Chem) α i and k om,i Significant range in O:C, even without accounting for aging. Is it enough to account for observed O:C? Is O:C a useful constraint?

14. Surface O:C SIMULATING THE O:C OF ORGANIC AEROSOL January 2006June 2006 Without aging surface O:C ranges from 0.2-0.8 (0.4 ± 0.1 for 60˚S to 60 ˚ N), with little seasonal difference. Dominated by POAi and isoprene SOA.

15. Base GEOS-Chem Simulation POAo: O:C=0.05, H:C=1.8 POAi: O:C=0.30, H:C=1.5 τ = 1.15 days COMPARISON WITH OBSERVATIONS O:C values captured near-source, but underestimated in aged environments. Mass underestimated in all environments… Thanks to several groups for providing data. More data from Jimenez Group and Qi Zhang will become available.

16. Revised Simulation (ASOA x 30) POAo: O:C=0.05, H:C=1.8 POAi: O:C=0.30, H:C=1.5 τ = 1.15 days HOW DOES INCREASING ASOA CHANGE THE PICTURE? Addition of ASOA improves model simulation of mass (as in Spracklen et al., 2011; Heald et al., 2011). O:C better captured in aged regions (BUT suggests we may need to invoke aging mechanisms), but O:C in source regions can now be overestimated (ASOA actually a source with lower O:C?) Bottom line: what mechanisms/sources can improve simulation of both mass and O:C?

17. MY TALK TODAY Part 3: Bewildering aerosol in the Southeastern US Part 1: Constraints on the global budget of OA Part 2: Impacts of the pine beetle infestation

18. PINE BEETLE INFESTATION IN WESTERN NORTH AMERICA Worst beetle outbreak in recorded history: peaked in BC in 2007 and in the Western US in 2009 [Kurz et al., 2008] Over 100,000 km 2 of forest killed, continued expansion. Impacts: carbon cycling, fire susceptibility. What about air quality?

19. VOCs ↓ Mortality Effect ↑ Attack Effect VOCs? O3O3 PINE BEETLES PERTURBING MONOTERPENE EMISSIONS Very few quantitative studies have been done Amin et al. (2012) measure emissions from Lodgepole pine (and spruce) under attack by mountain pine beetle, see significant enhancements of some emissions. Ashley Berg (CSU)

20. ESTIMATED IMPACTS ON MONOTERPENE EMISSIONS Largest impact of MPB on monoterpene emissions in British Columbia in 2004 (increase up to 70%) and in 2008 in US (increase up to 104%). Mortality Effect Mortality Effect + Attack Effect VEGETATION DISTRIBUTIONS (CLM4) ANNUAL MORTALITY (Meddens et al., in press) EXPERIMENTAL VOC INCREASES (Amin et al., 2012) VOC EMISSIONS IN CLM4 (MEGAN2.1) (Guenther et al., in press) β-pinene, β-phellandrene, 3-carene, P-cymene 2004 2008

21. ESTIMATED IMPACTS ON MONOTERPENE EMISSIONS [Berg et al., in prep] Mortality Effect Mortality Effect + Attack Effect 2004 2008 VEGETATION DISTRIBUTIONS (CLM4) ANNUAL MORTALITY (Meddens et al., in press) EXPERIMENTAL VOC INCREASES (Amin et al., 2012) VOC EMISSIONS IN CLM4 (MEGAN2.1) (Guenther et al., in press) CHAMBER SOA YIELDS (6-55%) (Lee et al., 2006) More muted impact on SOA (~30-40% max increases) but also more regional. Dependent on very uncertain species- variable response: scenario using spruce data shows up to doubling of SOA (1 µgm -3 increase). Evidence of importance of land use change in air quality.

22. MY TALK TODAY Part 3: Bewildering aerosol in the Southeastern US Part 1: Constraints on the global budget of OA Part 2: Impacts of the pine beetle infestation

23. IS OA CONTRIBUTING TO CLIMATE TRENDS IN SOUTHEASTERN US? [Portmann et al., 2009] Summertime trend in Maximum T (1950-2006) Data: Global Historical Climate Network Daily (GHCND) “Although clearly speculative, increasing biogenic secondary organic aerosol/cloud effects linked to forest regrowth and/or interactions with anthropogenic pollution is one possibility that is qualitatively consistent, not only with the spatial structure, but also with the seasonality of the correlation of the unusual negative temperature trends with precipitation found in the southeastern United States.” [Goldstein et al., 2009] Seasonal maximum in AOD consistent with biogenic emissions (implication: biogenic SOA). Part of the motivation for SOAS field campaign (summer 2013)! MISR: summer-winter AOD

24. IS THIS CONSISTENT WITH OUR UNDERSTANDING OF AEROSOL IN THE REGION? NO! Model shows significantly less seasonal enhancement over SE. But note: (a) diversity of satellite observations (b) model reproduces surface PM2.5 Bonne Ford (CSU)

25. IS THERE SEASONALITY IN SURFACE OA IN THE SOUTHEAST? NO. Seasonality in observed PM2.5 is largely driven by sulfate and dust. Consistent with Zhang et al. [2012] who suggest that seasonality is driven by meteorology, transport and photochemistry. * Assumed OM:OC=2 year-round

26. A ROLE FOR WATER UPTAKE? Very modest seasonality in surface layer RH, translates to very little seasonality in mass extinction efficiency. Not an artifact of the satellite overpass time (impact of water uptake on AOD is actually greater on 24-hr mean) Average nephelometer data at IMPROVE SE sites (2009) Mean diurnal RH in the SE(2009) A-train overpass

27. POSSIBLE MEANS OF RECONCILIATION: AEROSOL ALOFT CALIOP profiles over 3 years (2007-2009) show a summertime enhancement aloft – could be associated with fine inorganic or organic aerosol. Need an aircraft to tell! SENEX! Extinction [km -1 ] JJA [Ford and Heald, in prep]

28. CONCLUSIONS Models consistent with observed surface PM 2.5 loading and seasonality in the SE US, but underestimate summertime AOD (and seasonality) by a factor of 2-3. Possibly resolved by aerosol aloft (suggested by CALIOP)  aircraft observations during SOAS to solve the mystery! Models underestimate OA, but observations can narrow the range: suggest the “missing” source is “anthropogenic” and that additional sinks (fragmentation) may also be required. Oxygen content of aerosol is a useful constraint – suggests that aging mechanism required only in remote enviro. Pine beetle infestation in W North America estimated to be responsible for up to 40% increases in SOA. Required: better characterization of species-specific response