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

The roles of dust aerosols in atmospheric chemistry Direct impactIndirect impact Radiativeradiative forcing at TOA radiative forcing at the sfc heating/cooling actinic flux Chemical heterogeneous chemistry on dust surface photolysis Dust properties O 3, S O 2, NO 2, HNO 3 Radiative effect Chemical effect

The role of heterogeneous reaction on dust aerosols in the chemistry-climate system O 3 S O 2 NO 2 HNO 3 Size Composition Shape Mixing with other aerosols such as BC, OC, sulfate, nitrate, and sea-salt Direct impactIndirect impact Radiativeradiative forcing at TOA radiative forcing at the sfc heating/cooling actinic flux cloud properties Chemical heterogeneous chemistry on dust surface photolysis Hygroscopic CCN Dust properties

 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]. Limitations of past studies and motivation of this study 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.

Objectives Goals of this study To investigate how size and mineralogical compositions of dust affect heterogeneous loss rates (k het ) of gaseous species on particle surfaces and implication for the tropospheric photochemistry. 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.

Approach Mass transfer on dust particles and chemical properties of dust particles O 3, S O 2, NO 2, HNO 3 1. Alkalinity  Uptake acidic gases 2. Adsorption: SO 2 (g)+ O 2-  SO 3 2- SO 2 (g)+ OH -  HSO Oxidation: SO 3 2- (a)+ O 3 (g)  SO 4 2- (a)+ O 2 (g) HSO 3 - (a)+ O 3 (g)  HSO 4 - (a)+ O 2 (g) 4. Solubility 2HNO 3 + CaCO 3  Ca(NO 3 ) 2 + H 2 O + CO 2 (Krueger et al., 2003)  changes in morphology, solubility, scattering

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

Type of size-resolved mineral composition of dust aerosols REF (reference dust) BULK (bulk dust) FAC (fine and coarse dust) Approach 1234 REF (k het_ref )XX BULK (k het_bulk )XXX FAC (k het_fac )XXXX 1) Composition (uptake coefficient) 2) Size distribution 3) Mass fraction of mineralogical species 4) Mass partitioning of mineralogical species in fine and coarse modes

1) Uptake coefficients by main mineralogical compositions Three main mineral groups Mineral species or Alternative chemical elements Clay aggregatesKaolinite Illite Montrollinite α-Al 2 O 3 α-Fe 2 O 3 Calcite Dolomite CaCO 3 CaO MgO QuartzSiO 2 Authentic dust Table 1. Uptake coefficients

1) Uptake coefficients by main mineralogical compositions Three main mineral groups Mineral species or Alternative chemical elements Clay aggregatesKaolinite Illite Montrollinite α-Al 2 O 3 α-Fe 2 O 3 Calcite Dolomite CaCO 3 CaO MgO QuartzSiO 2 Authentic dust Table 1. Uptake coefficients

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

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

Results Reference Run (REF) : the effect of size distribution Figure 2. The values of k het of size-resolved mineral dust in REF for Saharan soil and China loess and BULK calcite, clay aggregate, and quartz using four dust size distribution. The values of k het varies by factor of 5 to 10 due to dust size distrubution. k het by authentic dust sample are different by factor of 5 for O 3 loss and two orders of magnitude for SO 2 loss.  The mineralogical composition of authentic dust is different and it can be represent a mixture of mineralogical compositions.

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

Results FAC Run (FAC) : the effect of mass partitioning of mineralogical species Figure 4. The values of k het 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. The larger mass fraction in fine mode, the higher values of k het

Results Sensitivity to controlling factors in heterogeneous loss rates Figure 5. The comparison of (average deviation)/(mean) of k het when the factors controlling k het considered for four heterogeneous loss rates. i)REF : Reaction with HNO 3 is the most sensitive to dust size distribution. ii)BULK : Reaction with O 3 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 k het is not abruptly changed. iv) For heterogeneous uptake, HNO 3 is the most sensitive to size-resolved mineralogical species. O 3 is also the same trends. Mass partitioning, size distribution, and mass fraction are important. v)SO 2 and NO 2 are similar characteristics in the ensitivity to the size-resolved mineral species. Mass partitioning, mass fraction, and size distribution are important.

Results Comparison between k het and J-values Figure 6. The heterogeneous loss rates and j-values of (a) O 3, (b) NO 2, and (c) HNO 3 when the dust layer is located 1 km to 2km. C04 size distribution and moderate dust loading 1500 ug/m 3 were considered. J[O 3 ( 1 D)]and J[O 3 ( 3 P)] are dominant process during the day. For NO 2, photolysis rates is dominant. For HNO 3 and SO 2, heterogeneous loss are a predominant process. We can asses each process more realistically in terms of size and composition of dust particles.

Conclusions ii ) The sensitivity of k het to mass fraction of mineral species depends on the relative contribution of mineralogical species to k het. The O 3 loss is the least sensitive to mass fractions because each mineral species play a role in O 3 uptake. i) The sensitivity of k het 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 iv) For controlling factors of k het, the magnitude of uptake coefficients is most important. k het of O 3 and k het of HNO 3 are sensitive to mass partitioning, size distribution, and then, mass fraction in decreasing order. k het of O 3 and k het of HNO 3 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 HNO 3 and SO 2 on dust particles are dominant process over photolysis rates. NO 2 uptake is slow process relative to photolysis. Heterogeneous loss rates of O 3 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. iii) The HNO 3 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 ~1.0x extremely large.

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