Ambient Elemental Carbon Concentrations

EC concentrations in rural and remote areas usually vary from 0.2 to 2.0 pg m-3 and from 1.5 to 20pgm-3 in urban areas. The concentration of EC over the remote oceans is approximately 5-20 ng m-3 (Clarke 1989). Average PM10 EC values exceeding 10 pg m 3 

TABLE 14.2 Elemental and Organic Carbon Percentages in Emissions by Different Sources 

Fuel Elemental Carbon Organic Carbon References 

TABLE 14.3 Measured Daily Average Elemental and Organic Carbon Concentration in a Series of U.S. Studies 

FIGURE 13.3 Annual mean EC concentration distribution in the United States based on samples from remote stations, (a) /xg m (b) percent of total aerosol mass. The influence of the urban centers has been eliminated to a large extent and the results depict the regional distributions (U.S. EPA, 1996). 

Southern California, and locally in the East. In the Northwest EC exceeds 10% of the aerosol mass, but over most of the United States it is less than 5%. 

FIGURE 13.4 EC size distribution measured inside a tunnel in Southern California. The distribution corresponds to the primary particles emitted by automobiles. Reprinted with permission from Venkataraman, C. and Friedlander, S. K. Size distributions of polycyclic hydrocarbons and elemental carbon. 1. Sampling, measurement methods and source characterization. Environ. Sci. Technol, 28. Copyright 1994 American Chemical Society. 

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If the blackness of the particulate matter collected on a filter is due to the graphitic carbon content of the sample, then the Km unit should convert to ambient elemental carbon concentrations. The form of that translation is apparent from the definition of the Km unit. Elemental carbon concentration measurements made by laboratory reflactometers calibrated against heated butane soot standards show that elemental carbon concentrations are linearly related to the log of the reflectance ratio R /R. Aerosol loadings stated in Km units should be directly proportional to elemental carbon concentrations sampled. 

A sampling schedule was designed which would encounter peak levels of ambient elemental carbon. Peak levels were of interest for two reasons to insure that filter loadings would be within the appropriate range for maximum analytical sensitivity and to expand the range of values over which the Km samplers could be calibrated. To determine when peak elemental carbon concentrations would be likely to occur, historical data on carbon monoxide... 

Fig. 9.1 Cell-quota theory for control of photo-autotroph growth by internal nitrogen or phosphorus. Q is the cell quota for the nutrient, in atoms of the element per atom of organic carbon. kfj is the minimum value, or subsistence quota. /////1IU1X gives growth as a proportion of maximum rate. The function 10) multiplies nutrient uptake (which is also a function of ambient concentration) and brings it towards zero as Q tends towards (i llax. The third part of the diagram compares typical ranges of values of cellular N and P content and show how these contribute to variation in the cell N P ratio.

Main mercury species in ambient air are elemental mercury (Hg°), reactive gaseous mercury (Hg(II)), mercury bound to aerosols, and methylmercury. Though dimethyl-mercury is together with Hg° the most volatile form of Hg, it has not been detected unequivocally in the atmosphere. Elemental mercury represents >95% of Hg in the atmosphere with ambient concentrations at the order of 1-5 ng m whereas MeHg in air was found to be in the range of 1 to 20 pg m (Pirrone et al. 2001). For this reason, in most cases mercury is pre-con-centrated on solid absorbers (gold, silver, activated carbon traps, etc.) prior to analysis (Drabaeck and Iverfeldt 1992, Horvat 1996). 

CMB Application to Central California PM Chow et al. (1992) apportioned source contributions to aerosol concentrations in the San Joaquin Valley of California. The source profiles used for CMB application are shown in Table 26.1. The standard deviations oa.. of the profiles (three or more samples were taken) are also included. To account for secondary aerosol components in the CMB calculations, ammonium sulfate, ammonium nitrate, sodium nitrate, and organic carbon were expressed as secondary source profiles using the stoichiometry of each compound. The average elemental concentrations observed at one of the receptors—Fresno, California, in 1988-1989— are shown in Table 26.2. The ambient concentrations of some species (c.g., Ga, As, Y, Mo, Ag) included in the source profiles were below the detection limits. These species... 

Dichloroethane (5 mL), carbon tetrachloride (15 mL), triethylamine (2 mL), acetonitrile (7 tnL), and 3 -azido-2,3 -dideoxythymidine (250 mg, 0.94 nunol) were placed in a threenecked flask equipped with magnetic stirrer, reflux condenser, dropping funnel, and inert-gas outlet. A solution of poly(oxyethylene H-phosphonate) (232 mg, 0.94 nunol of repealing units) in dichloroethane (5 mL) was added dropwise at ambient temperature under continuous stirring. The reaction was allowed to proceed for 24 h. After filtration of the precipitated triethylamine hydrochloride, the filtrate was concentrated and the polymer conjugate was precipitated by addition of diethyl ether. The isolated product was dried at 35-40 under reduced pressure (10 mbar). The elemental analysis of chlorine showed a trace of CI2. Yield was 485 mg (100%). 

The most important degradative method for the determination of urea in the natural water samples is based on its conversion to carbon dioxide and ammonia by hydrolysis obtained with a nickel metalloenzyme (urease). In the manual procedure outlined by McCarthy [89] for the analysis in seawater, the enzymatic hydrolysis of urea was carried out at 50°C for 20 min, in the range of pH from 6.4 to 8.0, using a solution of crude lyophilized jack beam urease. After the samples were cooled at room temperature, NH4 concentration was determined by manual colorimetric method after cooling the samples at room temperature. The ambient concentration of NH4 and the analytical blank (NH4 contained in the reagents and in the urease solution) have to be subtracted for any sample to obtain the concentration of urea. In this reference study, the precision (RSD) was 1% at the concentration of urea equal to 1 pmol N A manual indirect methodology was also described by Katz and Rechnitz [209] and the method was revised in other following studies [9,53,197,198]. It persists with minor modifications in recent works on the field and in culture experiments [71,199-202] and for determination of isotope ratio in urea by elemental... 

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