Organic Aerosol Components

In Eq. (LL), M is the concentration of the condensed-phase organic (in igm 3) available to absorb semivolatile organic products, ( is a constant that relates the concentration of the ith secondary organic aerosol component formed, C, to the amount of parent precursor organic reacted i.e., C, (ng m ) 1000a, A(parent organic in p,g m 3), and Kom i is the gas-particle partioning coefficient for the ith component. As discussed in more detail in Section D, Kim j is in effect an equilibrium constant between the condensed- and gas-phase concentrations. 

The studies of Facchini et al. (2000), Gysel et al. (2004), Kiss et al. (2005) and Dinar et al. (2006) highlight the importance of organic aerosol components in the cloud-nucleating activities of atmospheric particles. However, a question still remains to be answered What is the truly effect of organic components on aerosol CCN activity Furthermore, does the WSOM enhance cloud droplet activation or, on the other hand, delay droplet activation ... 

FoUcers M., Th. F. Mentel, A. Wahner, Influence of organic aerosol components on the reactivity of aqueous aerosols, Geophys. Res. Abst. 5 (2003a) 06053. 

FoUcers M., T.F. Mentel, H. Henk, R. Tillmanu, A. Wahner, R.P. Otjes, M.J. Blom and H.M. Ten Brink Partitioning of organic aerosol components between gas phase and particulate phase, Eos. Trans. AGU 84 (2003b) Fall Meet. Suppl., Abst. A51F-0746. 

The first section of this chapter is a review of fundamental chemical thermodynamic principles focusing on the chemical potential of species in the gas, aqueous, and solid phases. Further discussion of fundamentals of chemical thermodynamics can be found in Denbigh (1981). Chemical potentials form the basis for the development of a rigorous mathematical framework for the derivation of the equilibrium conditions between different phases. This framework is then applied to the partitioning of inorganic aerosol components (sulfate, nitrate, chloride, ammonium, and water) between the gas and particulate phases. The behavior of organic aerosol components will be discussed in Chapter 14. 

Table 14.8 presents chemical compounds that have been identified as primary organic aerosol components (Rogge et al. 1991, 1993a-e) together with their annual average... 

Table 13.8 presents chemical compounds that have been identified as primary organic aerosol components (Rogge et al., 1991, 1993a-e) together with their annual average ambient mass concentrations in the Los Angeles air basin. These ambient concentrations are the cumulative results of a variety of primary sources and secondary aerosol production. Normal alkanoic acids, aliphatic dicarboxylic acids, and aromatic polycarboxylic acids are... 

Hildebrandt L, Henry KM, Kroll JH, Worsnop DR, Pandis SN, Donahue NM (2011) Evaluating the mixing of organic aerosol components using high-resolution aerosol mass spectrometry. Environ Sci Technol 45(15) 6329-6335... 

Ng NL, Canagaratna MR, Zhang Q, Jimenez JL, Tian J, Ulbrich IM, Kroll JH, Docherty KS, Chhabra PS, Bahreini R, Murphy SM, Seinfeld JH, Hildebrandt L, Drmahue NM, DeCarlo PF, Lanz VA, Prevot ASH, Dinar E, Rudich Y, Worsnop DR (2010) Organic aerosol components observed in northern hemispheric datasets from aerosol mass spectrometry. Atmos Chem Phys 10(10) 4625 641. doi 10.5194/acp-10-4625-2010... 

ITie major component of atmospheric haze is sulfate particulate matter (particularly ammonium sulfate), along with varying amounts of nitrate particulate matter, which in some areas can equal the sulfate. Other components include graphitic material, fine fly ash, and organic aerosols. 

Also special care should be taken to reduce uncertainties on emission data and measurements. The validation of an aerosol model requires the analysis of the aerosol chemical composition for the main particulate species (ammonium, sulphate, nitrate and secondary organic aerosol). To find data to perform this kind of more complete evaluation is not always easy. The same applies to emissions data. The lack of detailed information regarding the chemical composition of aerosols obliges modellers to use previously defined aerosols components distributions, which are found in the literature. Present knowledge in emission processes is yet lacunal, especially concerning suspension and resuspension of deposited particles [37]. 

Chemical oxidation reactions and radical-induced hydrophobic-to-hydrophilic aging processes tend to increase the water solubility of OAs and, therefore, are thought to enhance the activity of atmospheric OAs as cloud condensation nuclei (CCN). As discussed by Gysel et al. (2004), at 75-90% of relative humidity (RH) the inorganic fraction dominates the water uptake (59-80%). Nevertheless, under the same conditions of RH, between 20% and 40% of total particulate water is associated with water-soluble organic matter. More data concerning the multiphase aerosol and cloud processes, as well as the chemical reactivity of carbonaceous aerosol components, have been compiled in the reviews of Jacobson et al. (2000), Kanakidou et al. (2005), and Poschl (2005) (and references therein). 

Most characteristic sizes of organic particles of marine aerosols do not exceed 10 pm. Data on organic aerosol are rather inadequate and do not even permit one to draw, in general terms, a reliable pattern of its optical properties. No doubt much effort is required before real possibilities appear to consider this component in a general model of aerosol. 

For NO t > 0-5 ppb (typical of urban and polluted rural sites in the eastern USA and Europe) Equations (3) and (4) represent the dominant reaction pathways for HO2 and RO2 radicals. In this case the rate of ozone formation is controlled largely by the rate of the initial reaction with hydrocarbons or CO (Equations (1) and (2)). Analogous reaction sequences lead to the formation of various other gas-phase components of photochemical smog (e.g., formaldehyde (HCHO) and PAN) and to the formation of organic aerosols. 

Water is a major component of the accumulation mode aerosol in amounts that depend on the relative humidity. The uptake of water is driven by the strongly hygroscopic nature of the secondary aerosol components, especially the ainmoniuin sulfates and nitrate. The water content depends in a complex way on both the inorganic and organic components. The resulting aerosol phase solutions are likely to be highly concentrated compared with fog droplets, for example. 

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