A.D. Clarke, V.N. Kapustin School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, USA

1. AEROSOL SIZE DISTRIBUTIONS, PROPERTIES AND VERTICAL PROFILES OVER THE PACIFIC: TOWARDS AN AEROSOL CLIMATOLOGY A.D. Clarke, V.N. Kapustin School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, USA

2. REGIONAL AEROSOL AND LONG RANGE TRANSPORT OVER THE PACIFIC A.D. Clarke, K.G.Moore, V.N. Kapustin School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, USA

3. FOCUS • Contribute to the understanding of the climatology and variability of aerosol over the remote oceans (Pacific) and the processes that establish its characteristics (size, concentration, chemistry, optical properties)

4. STUDY REGIONS • Various research programs have explored the aerosol fields in the Central Pacific remote marine boundary layer (MBL) and free troposphere (FT) - PEM-Tropics A&B, ACE-1, GLOBE 1&2, CPACE, SAGA 1, 2&3, RITS 88, 93&94 ...

5. WE HAVE OBSERVED • In regions free of continental influence the marine boundary layer (MBL) aerosol mass and optical properties are dominated by sea-salt (e.g. ACE-1 Tasmania ) with some natural sulfate. • Continental aerosol can influence or dominate (MBL) aerosol and optical properties over extensive regions until depleted by removal processes in MBL. • Lofting of continental aerosol above 2km often creates structured rivers of aerosol (dust, pollution) that is advected over global scales before re-entrainment into the surface boundary layer.

6. (CONT.) • Deep convection and precipitation removes MBL aerosol mass and number and vents cleaned surface air aloft. Can provide favorable region for natural nucleation with enhanced “new” aerosol number but with little mass. • Cloud venting aloft and larger scale subsidence and entrainment will couple free troposphere (FT) aerosol and MBL aerosol cycles including their evolution and properties. • Column aerosol properties (satellite) will reflect the above processes and a mix of natural and anthropogenically influenced aerosol. In general – surface based in-situ measurements will provide uncertain assessments of column aerosol properties.

7. Aerosol Size Distributions - Basics and Interpretation Modal structure of an MBL aerosol MBL processes FT processes MBL - polluted and clean case Volatility and size distributions

8. Size Distributions and Volatility as a Tool to Study Particles Composition

9. Comments • Page • Size Distributions and Volatility... • Some selected examples of size distributions (number, surface, volume) for various cases (clean/polluted free troposphere - FT, clean/polluted marine boundary layer -MBL). • Some related properties (single scattering albedo - ω, scattering coefficient, surface area and refractory volume fraction) indicated in panels on the left. • Page • RCN Ratio - an Indicator .. • A lidar image from the NASA DC8 at 8-10km from Darwin to Tokyo. • Variable low level clouds are evident alone with a dramatic Asian dust plume reaching 7km over Japan. • Regions of no backscatter are very clean regions where elevated new particle concentrations can be see over the ITCZ and where refractory surface derived CNs (@300C) are at minimum.

10. Zonal Aerosol Features in the Pacific Free Troposphere (FT) • A flight from Darwin to Tokyo revealed zonal variations in aerosol properties. Enhanced nucleation in clean air near the equator changed to continental air aloft above Tokyo with high mass loading and large surface derived refractory aerosol fraction. • The ratio of total (UCN) to larger CN and ratio of refractory CN (soot, dust, sea salt) to total CN show zonal regions aloft where clean or polluted air is most prevalent.

11. INDOEX99 - Aerosol Plumes from India.

12. Regional haze(biomass) Structure of Aerosol Plumes over Pacific South America Pollution (PEMT-A) Clean marine air

13. Structure of Aerosol Plumes over PacificAfrican Biomass Burning (PEMT-A) NASA PEMT-A E. Browell

14. Structure of Aerosol Plumes over Pacific African Biomass Burning (cont.)

15. Variability of Aerosol Size Distributions • A PEMT flight over the ITCZ and the SPCZ separated by a zone of subsidence. • Marked changes in aerosol size reveal regions of nucleation aloft above the ITCZ and SPCZ, with larger aerosol at intermediate altitudes. • Size distributions in the MBL are even larger and show a cloud processed mode with intermodal minimum near 0.09 um.

16. Number Concentration is Enhanced in FT as the Result of New Particles Production. A 3D latitude-longitude distributions of small differential condensation nuclei - DCN (3nm<Dp<12nm) are highest aloft (above 3km) near ITCZ and SPCZ and almost no DCN particles are present in the MBL (observations from all PEM Tropics flights).

17. Zonal Structure of MBL Aerosol Size Distributions The data suggest some predictable features of the size distributions associated with key meteorological zones in the Pacific. Each zone has characteristic aerosol sources (natural and anthropogenic) and mean processes associated with FT/MBL exchange, removal mechanisms, wind and cloud fields. The modulations in MBL aerosol number distributions in passing through the key Pacific meteorological zones. Covert et al.

18. FT / MBL exchange and size distributionsin the equatorial Pacific An example of a sharp transition to aged MBL equatorial region aerosol upon passing through SPCZ region with strong convection. Cloud processed bimodal structure is the most obvious signature of the MBL aerosol in equatorial regions. Exchange with FT also plays a major role in shaping size distribution (note the same size of the particles below and just above inversion).

19. FT / MBL exchange and size distributionsin the equatorial Pacific (cont.) A vertical profile near the ITCZ shows recent nucleation near 4 km with monomodal aerosol size increasing as particles subside toward the inversion near 1km. Below the inversion the particles entrained into MBL become bimodal as a result of MBL cloud processing. FT/MBL exchange affects shape the size distributions: UFCN (Dp<20nm) appeared in the MBL after the frontal passage (a) and as the result of cumulus clouds mixing( b). No UFCN (<20nm) during the stratus clouds period (c).

20. Some Aerosol Optical and Microphysical Properties of Aerosol Plumes over South Pacific Scattering vs. absorption coefficients suggest a typical single scattering albedo of 0.81 Submicrometer scattering and volume are strongly linear indicating a similar particle size independent of concentration Submicrometer total and refractory (soot) volume are related for these plumes indicating similar refractory fraction in aerosol Light absorption and refractory volume are related with values indicative of a soot carbon core

21. CONCLUSIONS • The relative simplicity of an unperturbed marine aerosol system makes it possible to identify links of FT and MBL size distributions to regional meteorological regimes and processes • The evaporating regions of ITCZ cloud outflow layers [4 to >12km] are sources of new particles (nucleation) that could populate extensive regions of the tropical free troposphere. • Nucleation is linked to elevated sulfuric acid derived from oceanic DMS for these near-cloud environments and appeared consistent with classical binary nucleation theory.

22. CONCLUSIONS (cont.) • Exchange (entrainment/subsidence) with the free troposphere (FT) plays a major role in shaping the particle size distribution in the remote MBL. • Cloud processing of the aerosols have an important effect on aerosol size distributions in the MBL and the bimodal structure is the most obvious signature of the MBL aerosol in equatorial regions. • The relative simplicity of an unperturbed marine aerosol system makes it possible to identify links of FT and MBL size distributions to regional meteorological regimes and processes