Acidity, in atmospheric aerosol

One other in situ technique can be used to determine fractional acidity in atmospheric aerosols by means of Fourier transform infrared (FTIR) spectroscopy (46). Originally, impactor samples were collected and were pressed into a KBr matrix, and then the IR spectrum was taken by attenuated total reflectance (ATR) FTIR spectroscopy to determine relative acidity, based on differences in absorption bands for sulfate and bisulfate species. Aerosols with [H+]/[S042 ] ratios greater than 1 could also be qualitatively identified. More recent innovations in the FTIR technique (47, 48) have made possible... 

Data from Adler, H., Siren, H., Kulmala, M., and Riekkola, M. L., Capillary electrophoretic separation of dicarboxylic acids in atmospheric aerosol particles, J. Chromatogr. A, 990, 133-141, 2003. 

E. Dabek-Zlotorzynska, M. Piechowski, M. McGrath and E.P.C. Lai, Determination of low-molecular-mass carboxylic acids in atmospheric aerosol and vehicle emission samples by capillary electrophoresis, J. Chromatogr. A, 910, 331-345, 2001. 

Kawamura K, Watanabe T (2004) Determinatitm of stable carbon isotopic compositions of low molecular weight dicarboxylic acids and ketocarboxylic acids in atmospheric aerosol and snow samples. Anal Chem 76 5762... 

Continuous Sampling and Determination. There are no truly continuous techniques for the direct determination of sulfuric acid or other strong acid species in atmospheric aerosols. The closest candidate method is a further modification of the sensitivity-enhanced, flame photometric detector, in which two detectors are used, one with a room-temperature de-nuder and one with a denuder tube heated to about 120 °C. Sulfuric acid is potentially determined as the difference between the two channels. In fact, a device based on this approach did not perform well in ambient air sampling (Tanner and Springston, unpublished data, 1990). Even with the SF6-doped H.2 fuel gas for enhanced sensitivity, the limit of detection is unsuitably high (5 xg/m3 or greater) because of the difficulty in calibrating the two separate FPD channels with aerosol sulfates. 

Modified filter sampling methods that are available will measure ambient levels of strong acid in ambient aerosol samples, and these methods do so with acceptable precision and accuracy [as indicated by the balance between measured anions and cations (56, 57)] in the absence of significant levels of particulate weak acids. Additional intercomparisons involving intrinsically different techniques for particulate strong acidity [e.g., IR spectroscopy (48), thermal speciation (38, 45), and filter methods (28)] are needed. Further information on the occurrence of various weak acids in airborne particles is needed, along with further studies of techniques for their specific determination in atmospheric aerosol samples. 

Sulfuric acid may be determined in the presence of other acidic aerosol constituents, but no method for the separation and determination of bisulfate, the most common acidic species in atmospheric aerosols, has been successfully developed. 

Milne, P. J., and R. G. Zita. 1993. Amino acid nitrogen in atmospheric aerosols Occurrence, sources and photochemical modification. Journal of Atmospheric Chemistry 16 361-398. 

Chan, M. N., Choi, M. Y., Ng, N. L., and Chan, C. K. (2005). Hygroscopicity of water-soluble organic compounds in atmospheric aerosols Amino acids and biomass burning derived organic species. Environ. Sci. Technol. 39,1555-1562. 

We focus initially on the photochemical behaviour of complexes of Fe(III) with simple carboxylic acids and give particular attention to oxalic acid. This compound is prevalent in atmospheric aerosols [28], provides a simple example of environmentally important light-mediated ligand-to-metal charge transfer (LMCT) processes which result in ligand decarboxylation [27] and is used to initiate the degradation of contaminants both in the absence and presence of added hydrogen peroxide (via the so-called modified photo-Fenton process [29,30]). In addition, the photochemistry of Fe(III)-oxalate complexes has been studied in detail, as it is the basis of... 

Table 10-5 Oxy acids, their salts, and ionized forms which could exist in atmospheric aerosol particles...

The total aerosol mass during the variation of total ammonia in the system is also shown in Figure 10.17. One would expect that an increase of the availability of NH3, an aerosol precursor, would result in a monotonic increase of the total aerosol mass. This is not the case for at least the ammonia-poor conditions (ammonia/sulfuric acid molar ratio less than 1). The increase of NH3 in this range results in a reduction of the H2S04(aq) and the accompanying water. The overall aerosol mass decreases mainly because of the loss of water, reaching a minimum for an ammonia concentration of 1.8 pg m-3. Further increases of ammonia result in increases of the overall aerosol mass. This nonlinear response of the aerosol mass to changes in the concentration of an aerosol precursor is encountered often in atmospheric aerosol thermodynamics. 

Potukuchi, S. and Wexler, A. S. (1995a) Identifying solid-aqueous phase transitions in atmospheric aerosols. I. Neutral acidity solutions, Atmos. Environ, 29, 1663-1676. 

Li, Y.-C. Yu, J.Z. Simultaneous determination of mono- and dicarboxylic acids, omega-Oxo-carboxyUc acids, midchain ketocarboxylic acids, and aldehydes in atmospheric aerosol samples. Environ. Sci. Technol. 2005, 39, 7616-7624. 

Reemtsma, T., A. These, P. Venkatachari, X.Y. Xia, P.K. Hopke, A. Springer, and M. Linscheid (2006), Identification of fulvic acids and sulfated and nitrated analogues in atmospheric aerosol by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry, Anal. Chem., 78, 8299-8304. 

Aerosol Dynamics. Inclusion of a description of aerosol dynamics within air quaUty models is of primary importance because of the health effects associated with fine particles in the atmosphere, visibiUty deterioration, and the acid deposition problem. Aerosol dynamics differ markedly from gaseous pollutant dynamics in that particles come in a continuous distribution of sizes and can coagulate, evaporate, grow in size by condensation, be formed by nucleation, or be deposited by sedimentation. Furthermore, the species mass concentration alone does not fliUy characterize the aerosol. The particle size distribution, which changes as a function of time, and size-dependent composition determine the fate of particulate air pollutants and their... 

Alternatively, in the presence of particulate matter and aerosols, sulfur dioxide may react with atmospheric oxygen to form sulfur trioxide, which forms sulfuric acid, a strong acid, in water ... 

Chemical interactions also occur in the condensed phases. Some of these are expected to be quite complex, e.g., the reactions of free radicals on the surfaces of or within aerosol particles. Simpler sorts of interactions also exist. Perhaps the best understood is the acid-base relationship of NH3 with strong acids in aerosol particles and in liquid water (see Chapter 16). Often, the main strong acid in the atmosphere is H2SO4, and one may consider the nature of the system consisting of H2O (liquid), NH3, H2SO4, and CO2 under realistic atmospheric conditions. Carbon dioxide is not usually important to the acidity of atmospheric liquid water (Charlson and Rodhe, 1982) the dominant effects are due to NH3 and H2SO4. The sensitivity the pH of cloud (or rainwater produced from it) to NH3 and... 

In its pure form, nitric acid is a liquid with a high vapor pressure (47.6 torr at 20°C), so that in the lower atmosphere HNO3 exists as a gas, in an aerosol or in a cloud droplet. When nitric acid reacts with a base a nitrate salt is produced, if... 

All of these species are very soluble in a rain or cloud drop and are an important source of atmospheric aerosols. For ammonia and ammonium, the condensed phases (I and s) represent approximately two-thirds of the total atmospheric burden, whereas for nitric acid and nitrates, about two-thirds is in the gas phase (Soderlund and Svensson, 1976). 

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