Aerosol Physicochemical Properties Breakout Group

1. Aerosol Physicochemical Properties Breakout Group Workshop SummaryMILAGRO science meeting25 Oct. 2006Part 1: Nuggets (i.e. preliminary findings)Co-Chairs:Bety Cardenas, Tony Clarke, Jim Smith, Jose-Luis Jimenez

2. All C-130 Milagro Flight Tracks

3. Nuggets: Emissions/Sources • Lead a major component of PM2.5 • Pb, Zn, and Cl are high in PM2.5 particles at T0 • Pb is predominantly associated with SO42- particles at T0 • Plumes of almost 1 mg m-3 of Pb at Tula Nuggets: Evolution of Properties/Aging • While NOx/NOy going from 1 to 0.1 (aging), ratio of organics/CO increases x10. Light absorption/CO increases x2. (G-1) • Increases continue for longer time scales (1-day, comparing to C-130). • Same effect comparing T0 and Tres Padres, but smaller presumably because of shorter times. Nuggets: Physical Properties • Internal mixing happens quickly (~ few hrs). • Fractal soot particles get coated and become spherical over the course of the morning, J. Slowik, BC & ARI • Consistent observations with T0 and T1 (more fractal at T0 usually)

4. Nuggets: New Particle Formation • Regarding measurements at T1 (McMurray et al.): • - NPF occurred frequently, ion-induced nucleation not significant. • - Can infer particle sub 5-nm growth rates from charge distributions. • - New particles varied proportionally to H2SO4. • - Enhancement of both NH4+ and dimethylamine in new particles from nucleation (10 nm). • - NPF frequently evident at boundary between BL and free trop, also boundaries of plumes. C-130 - First airborne deployment of new FMPS (TSI) with 1Hz sizing from 7nm reveals details of nuclei distribution and evolution. Vertical profile inversion A. Clarke, V. Kapustin,S. Howell, J. Zhou, C. McNaughton, Y. Shinozuka University of Hawaii

5. Aerosol Intercomparisons (AMS and light scattering) Outside City • 3/10/06 MIRAGE Flight • 15 Second AMS PM1 mass compares well with PM1 Light Scattering • Other flights show good correlation as well DeCarlo, Dunlea, and Jimenez, CU Clarke et al.-UH

6. Aerosol Chemistry 3/8/06 HCN measured by Caltech CO measured by NCAR For more see the Poster by DeCarlo, Dunlea, and Jimenez, CU

7. Nuggets: Chemical Properties • Most of (NH4)2SO4 particles are internally mixed with Si and K (TEM). • Organics in particles at T0: • High proportion of oxygenated organics than primary • Oxygenated organics were less volatile than primary organics at T0 • Nitrate: • Rapid partitioning of NO3- between gas and aerosol phase (from G-1). HNO3 equilibrium w/ particles changes w/ photochemical age. • High nitrate in growing newly formed particles at T1. • Shift in NO3- partitioning due to dilution between T0 and Pico Tres Padres • Ca in coarse mode particles: • T1: Ca dominates PM2.5 – PM1 during dusty period up to March 21 • PM coarse fraction at Tula is dominated by Ca. Many unidentified compounds (60% of mass) in PM10. • T0: Ca dust comes from Tula region. • Higher concentrations of metals and Hg at T1 than T0. But total gaseous Hg higher at T0 than T1.

8. Nuggets: Hygroscopicity/CCN • During new particle formation, particles activated at S=0.15 are smaller and less hygroscopic than at other times. • S-classified particles are less hygroscopic than would be predicted. • Hygroscopicity increases with age in Mexico City plume from C130 measurements. • At T1 hygroscopicity increases at midday, coinciding with NPF events. • CCN indicates high fraction of insoluble material in activated particles.

9. SOA, Light Absorption, ω0 & Composition Effects of Ageing - Mexico City G-1 Obs. (L. Kleinman) Photochemical age = -Log(NOx/NOy) Dilution accompanies ageing Fresh emissions over city. NOx/NOy near 1, "Age" = 0 Aged pollutants over T1 and T2. NOx/NOy = 0.1, "Age" =1 (7h at OH = 107) Ratio of Organic Aerosol (AMS) and Aerosol light absorption (PSAP) to CO will show effect of ageing on SOA and Specific Light Absorption Kleinman, Springston, Senum, Lee, Wang, Nunnermacker, Daum, Weinstein-Lloyd, Hubbe, Ortega, Alexander, Jayne, Canagaratna

10. Ageing:● Screen data to minimize non-urban sources ● Assume BC/CO emission ratio is constant ● Bin data by age, Calc. regression slopes vs. CO and 2 σ For Age change from 0 to 1: ● Specific Light Absorption (absorption/BC) increases by 60% - lensing effect ● Organic Aerosol increases 8-fold – SOA production

11. Single Scatter Albedo As Age Increases: ● Aerosol mass and scattering (normalized to CO) increases ● Aerosol light absorption (normalized to CO) increases ● Light scattering wins, Single Scatter Albedo increases

12. Aerosol Composition ● Organic and Sulfate fractions increase with Age ● Nitrate decreases as HNO3 evaporates

13. Part 2: Collaboration Ideas / Suggestions / Needs Photo by C. McNaughton

14. Collaborations: General Issues • Need a data catalog for all measurements that exist (L. Kleinman). • Important to compare the meteorological data at T1 between the different datasets available. (T. Castro). • There are some gaps, not clear yet whether there are disagreements. Groups at T1 should be aware of this. • How to merge the measurements of the aircraft and the surface sites? (G. Sosa) • Compare directly the aircraft measurements directly over the urban area (R. Zaveri). • Use back-trajectories arising from MC and flag times the C-130 and DC-8 saw air from the city (T. Clarke). • Jerome Fast & Ben de Foy have generated and will share many model products for meteorology. Some of them on the web (mce2.org),

15. Meteorological Overview of MILAGROJerome D. Fast, Pacific Northwest National Laboratory Objective:Provide the meteorological context that affects the transport, mixing, transformation, and fate of trace gases and particulates in the vicinity of Mexico. • three cold surges affected local and regional meteorology (3rd strongest) over the central Mexican plateau • analyzed wide range of MILAGRO field measurements to divide field campaign into 3 meteorological regimes 1) prior to Norte #1: mostly sunny, dry 2) Norte #1 - #3: increased humidity, cloudiness, and afternoon convection 3) after Norte #3: further increase in humidity, cloudiness, afternoon convection, and showers Identified periods favorable for pollutant transport from Mexico City towards T1/T2 downwind sampling sites and the Gulf of Mexico (gray shading) - more detailed trajectory analyses to follow • meteorological overview paper now on-line in MILAGRO special issue of ACPD

16. Local and Regional Modeling of Particulates and Aerosol Radiative ForcingJerome D. Fast, Pacific Northwest National Laboratory Objective:Use fully-coupled meteorological-chemical-aerosol model (WRF-chem) and measurements from a wide range of platforms (surface, aircraft, satellite) to examine particulate evolution and aerosol radiative forcing over Mexico. Observed AOD 21 UTC 19 March Predicted AOD Predicted Radiation & AOD Grid 1: x=22.5 km Grid 3: x=2.5 km 0.1 aerosol transport T2 peak AOD ~0.6 T1 peak AOD ~ 1.4 cloud extent GOES Aerosol and Smoke Product (GASP) simulation without high-resolution domains (x=2.5 and x=7.5 km) results in AOD lower than observed over both central Mexico and downwind over Gulf of Mexico shortwave radiation reduced by as much as 100 W m-2 primarily from biomass burning plumes on this day

17. Collab: Emissions / Sources • Need chemical characterization of various sources for CMB analysis. Elizabeth Vega, IMP. Collab: Evolution of Properties • Issue of “clocks” for evolution was discussed in detail in aerosol optics & radiation session. It is important for that group, to correlate optical evolution with physico-chemical properties evolution. • Needs collaboration between these two groups Collab: Physical Properties • Help on validating and interpreting RAMA network’s new PM2.5 measurements (TEOM, Beta, etc.). B. Cardenas, CENICA. • Need information relating to volatilization of aerosols entering aircraft. (eg. ammonium nitrate?) T. Clarke, Hawaii. • Many groups performed various microscopy techniques, good opportunity to compare & collaborate. B. Cardenas, CENICA.

18. Collab: Chemical Properties • Interest in collaborations investigating: • PAHs (G. Mejia / Marr / Gaffney / Jimenez) • Metals (Sosa / Onasch / Salcedo / Laskin) • Organic nitrates (Gaffney/Jimenez) • Organosulfates (Jimenez) • Amines (Moffet / Jimenez) • Oxalic acid (Moffet) • Nitrate in nanoparticles (J. Smith) • U, Th, and K in filters (E. Herrera) • Size-resolved composition (Mamani / Castro / Laskin / Sosa / Onasch / Jimenez) • Multiple groups are going to investigate SOA formation rates and yields, need to collaborate across time scales. (Kleinman, DeCarlo, Volkamer, Worsnop, Jimenez, etc.) • Relative importance of burning in urban emissions and concentrations (POA and SOA) (many groups) • Relative importance of dust vs. fine particles (J. Dibb)

19. Collab: New Particle Formation • Comparisons between ground and aircraft for NPF would be very useful, not usually done. • P. McMurry & Tony Clarke will collaborate on this. • Comparisons between ground sites on dynamics of NPF are possible • Most extensive data at T1 (McMurry / Smith), also at Pico Tres Padres (Worsnop) and T0 (Jimenez) • Mexico City had “tomato events” instead of “banana events” (P. McMurry)

20. Collaborations: Satellites • Need aerosol data to study how well and how far can MC plume be detected from satellites, and on which conditions this depends. Also trying to classify particle types. Summary of morning discussion from S. Massie, NCAR. Collaborations: Models • Need gas and particle data to compare with model output (R. Zaveri)

21. List of topics and number of proposed papers • Emissions / Sources (3) • Physical properties (12) • Chemical properties (23) • Hygroscopicity & CCN (6) • Evolution of properties (9) • New Particle Formation (5) • Models (2) • Satellites (0) • Health effects (6)