Advisor: Prof. Irina N. Sokolik Gill-Ran Jeong

1. The effects of size-resolved mineralogical composition on heterogeneous chemistry on dust particle surfaces Advisor: Prof. Irina N. Sokolik Gill-Ran Jeong The 4th Earth and Atmospheric Sciences Graduate Symposium, November 10th, 2006

2. The roles of dust aerosols in atmospheric chemistry Chemical effect O3, SO2,NO2, HNO3 Radiative effect Dust properties Direct impact Indirect impact Radiative radiative forcing at TOA radiative forcing at the sfc heating/cooling actinic flux heterogeneous chemistry on dust surface photolysis Chemical

3. The role of heterogeneous reaction on dust aerosols in the chemistry-climate system • Size • Composition • Shape • Mixing with other aerosols • such as BC, OC, sulfate, • nitrate, and sea-salt O3 SO2 NO2 HNO3 Dust properties Direct impact Indirect impact Radiative radiative forcing at TOA radiative forcing at the sfc heating/cooling actinic flux cloud properties heterogeneous chemistry on dust surface photolysis Chemical CCN Hygroscopic

4. Limitations of past studies and motivation of this study •  Size distributions • commonly-known dust size distributions, • a single mode size distribution, • a few size bins [D’Almeida, 1987; Jaenicke et al., 1993; Kopke et al., 1997; Zhang et al., 1999; Liao et al., 2003; Bian and Zender, 2003; Tang et al., 2004; Bauer et al., 2004, 2005; Martin et al., 2003]. •  Uptake coefficients • one uptake coefficient of a particular chemical element or mineral species based on laboratory measurement and modeling [Bauer et al., 2004, 2005; Zhang and Carmichael, 1999; Dentener et al., 1996; Bian and Zender, 2003; Martin et al., 2002, 2003; Liao et al., 2003, 2004; Usher et a;., 2002]. •  A mixture of mineralogy of dust • Because the mineralogy of dust particles varies even though the similar chemical elements consist of dusts [Berry et al., 1983; Anthony ] • The abundance of minerals also varies with dust source region or transportation or aging of dust [Glaccum and Prospero, 1980]. The importance of size and compositions of mineral dust in modeling and measurement study. (Usher et al., 2002). Therefore, we need to construct size-resolved mineral composition of dust aerosols in order to investigate the effects of dust size distribution and compositions on the heterogeneous loss rates.

5. Objectives 1. To construct size-resolved mineralogical composition of dust particles by selecting the range of mass fraction of the three main mineralogical compositions, particularly considering the alkalinity from carbonate-containing species and iron oxide contents in clay aggregates, pursuing consistent treatment of mineral dust aerosols in both chemistry and radioactive modeling. 2. To calculate heterogeneous loss rates on dust particles by integrating a gas-to-particle diffusion rate constant using the Fuchs-Sutugin approximation in the transition regime. The recent data on uptake coefficients of individual minerals and authentic dust and several dust size distributions reported from field and laboratory experiments were used. Goals of this study To investigate how size and mineralogical compositions of dust affect heterogeneous loss rates (khet) of gaseous species on particle surfaces and implication for the tropospheric photochemistry.

6. Approach Mass transfer on dust particles and chemical properties of dust particles O3, SO2,NO2, HNO3 1. Alkalinity  Uptake acidic gases 2. Adsorption: SO2 (g)+ O2- SO32- SO2 (g)+ OH- HSO3- 3. Oxidation: SO32-(a)+ O3(g) SO42-(a)+ O2(g) HSO3-(a)+ O3(g) HSO4-(a)+ O2(g) 4. Solubility 2HNO3 + CaCO3 Ca(NO3)2 + H2O + CO2 (Krueger et al., 2003) changes in morphology, solubility, scattering

7. Approach The overall heterogeneous loss rates of a gaseous species j, kj L is the number of types of mineral compounds. kp,j is the overall heterogeneous loss rate of gaseous species j on the surface of material compound p γp,j, : uptake coefficient of gaseous species j by mineral compound p np(r) is the size distribution of mineral compound p F(r, γp,j) is mass transfer coefficient whereby the Fuchs-Sutugin approximation is applied to the gas-to-particle diffusion in the transition regime. Iron-oxide clay aggregates Calcite (carbonate-containing minerals) Quartz: a non-absorbing and inactive mineral of gaseous uptake.

8. Approach Type of size-resolved mineral composition of dust aerosols REF (reference dust) 1) Composition (uptake coefficient) 2) Size distribution 3) Mass fraction of mineralogical species 4) Mass partitioning of mineralogical species in fine and coarse modes BULK (bulk dust) FAC (fine and coarse dust)

9. 1) Uptake coefficients by main mineralogical compositions Table 1. Uptake coefficients

10. 1) Uptake coefficients by main mineralogical compositions Table 1. Uptake coefficients

11. 2) Dust size distribution 2.5μm of SMD Table 2. dust size distribution Where GMD indicates geometric medium diameter. SMD is surface medium diameter. SMD=GMD*exp(3*ln2(GSD)) MMD is mass medium diameter. MMD=GMD*exp(2*ln2(GSD))

12. 3) Mass fraction and mass partitioning in size-resolved mineralogical species Table 3. mass fraction and mass partitioning (a) Reference dust REF (b) Bulk dust BULK (c) Fine and coarse dust FAC

13. Results Reference Run (REF) : the effect of size distribution • The values of khetvaries • by factor of 5 to 10 due to dust size distrubution. • khet by authentic dust • sample are different by factor of 5 for O3 loss and two orders of magnitude for SO2 loss.  The mineralogical composition of authentic dust is different and it can be represent a mixture of mineralogical compositions. Figure 2. The values of khetof size-resolved mineral dust in REF for Saharan soil and China loess and BULK calcite, clay aggregate, and quartz using four dust size distribution.

14. Results BULK Run (BULK) : the effect of mass fraction of mineralogical species The sensitivity of khet to mass fraction depends on the relative contribution of each mineral species to k_het. Figure 3. The values of khet of BULK size-resolved mineralogical species with different mass fractions of mineralogical compositions for C04 size distribution.

15. Results FAC Run (FAC) : the effect of mass partitioning of mineralogical species The larger mass fraction in fine mode, the higher values of khet Figure 4. The values of khet of FAC size-resolved mineralogical species with mass partitioning of fine and coarse modes for BULK_C04_exp as well as BULK model for C04 size distribution.

16. Results Sensitivity to controlling factors in heterogeneous loss rates • REF : Reaction with HNO3 is the most sensitive to dust size distribution. • BULK : Reaction with O3 is the least sensitive to mass fraction of mineralogical species. • iii) FAC : Unlike the mass fraction, mass partitioning is significantly affected by the dust size distribution. • D87 has the largest ratio and O98 is the least ratio. Because the relatively small fine mode in D87 size distribution, however, • fine mode distribution occupied in relatively wide range of size distribution in O98 size distribution, the khet is not abruptly changed. • iv) For heterogeneous uptake, HNO3 is the most sensitive • to size-resolved mineralogical species. O3 is also the • same trends. Mass partitioning, size distribution, and mass fraction are important. • SO2 and NO2 are similar characteristics in the ensitivity to the size-resolved mineral species. Mass partitioning, mass fraction, and size distribution are important. Figure 5. The comparison of (average deviation)/(mean) of khet when the factors controlling khet considered for four heterogeneous loss rates.

17. Results Comparison between khet and J-values Figure 6. The heterogeneous loss rates and j-values of (a) O3, (b) NO2, and (c) HNO3 when the dust layer is located 1 km to 2km. C04 size distribution and moderate dust loading 1500 ug/m3 were considered. J[O3(1D)]and J[O3(3P)] are dominant process during the day. For NO2, photolysis rates is dominant. For HNO3 and SO2, heterogeneous loss are a predominant process. We can asses each process more realistically in terms of size and composition of dust particles.

18. Conclusions i) The sensitivity of khet to size distribution is the largest in B02 size distribution and the smallest in C04 size distribution. In comparison with photolysis study, J-values are the largest in O98 size distribution and the smallest in C04 size distribution • ii ) The sensitivity of khet to mass fraction of mineral species depends on the relative contribution of mineralogical species to khet. The O3 loss is the least sensitive to mass fractions because each mineral species play a role in O3 uptake. iii) The HNO3 is the most sensitive to the mass partitioning not only because large difference in uptake coefficients but also the order of uptake coefficients is 1.0 x 10-2~1.0x 10-1 extremely large. iv) For controlling factors of khet, the magnitude of uptake coefficients is most important. khet of O3 and khet of HNO3 are sensitive to mass partitioning, size distribution, and then, mass fraction in decreasing order. khet of O3 and khet of HNO3 show similar characteristics in the sensitivity to the size-resolved mineral species. Mass partitioning, mass fraction, and size distribution are important in decreasing order. v) Heterogeneous reaction of HNO3 and SO2 on dust particles are dominant process over photolysis rates. NO2 uptake is slow process relativeto photolysis. Heterogeneous loss rates of O3 varies over one order of magnitude due to size-resolved mineral species and its has the same order of magnitude to that of the photolysis.

19. Appendix REF, BULK, and FAC Run Figure 5. The values of khet of REF, BULK, and FAC size resolved mineralogical species.