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In principle, mass concentrations of black carbon (BC) (MBC) can be estimated by the measurement of the light absorption coefficient of BC. Filter-based methods, which quantify the absorption coefficient (babs) from the change in transmission through a filter loaded with particles, have been widely used to measure MBC. However, reliable determination of MBC has been very difficult because of the large variability in the mass absorption cross section (Cabs), which is the conversion factor from babs to MBC. Coating of BC by volatile compounds and the co-existence of light-scattering particles contribute to the variability of Cabs. In order to overcome this difficulty, volatile aerosol components were removed before collection of BC particles on filters by heating a section of the inlet to 400°C. We made simultaneous measurements of babs by two types of photometers (Particle Soot Absorption Photometer (PSAP) and Continuous Soot Monitoring System (COSMOS)) together with MBC by an EC-OC analyzer to determine Cabs at 6 locations in Asia. Cabs was stable at 10.5 ± 0.7 m2 g-1 at a wavelength of 565 nm for BC strongly impacted by emissions from vehicles and biomass burning. The stable Cabs value provides a firm basis for its use in estimating MBC by COSMOS and PSAP with an accuracy of about 10%. For the quantitative interpretation of the ratio of the Cabs to the model-calculated Cabs*, we measured Cabs for mono-disperse nigrosin particles in the laboratory. The Cabs/Cabs* ratio was 1.4-1.9 at the 100-200 nm diameters, explaining the ratio of 1.8 for ambient BC. [ABSTRACT FROM AUTHOR]

We examined the prevalence of extended-spectrum beta-lactamase (ESBL)-producing strains of Klebsiella pneumoniae, Klebsiella oxytoca, Escherichia coli, Proteus mirabilis, Citrobacter koseri, and Salmonella spp. that were isolated as part of the SENTRY Asia-Pacific Surveillance Program between 1998 and 2002. During the study period, a total of 6,388 strains were gathered from 17 medical centers in 7 countries and examined for ESBL production and hyperproduction of K. oxytoca chromosomal K1 beta-lactamase enzyme. High rates of confirmed ESBL-producing isolates were found in K. pneumoniae strains from Singapore (35.6%), followed by those from mainland China (30.7%), South Africa (28.1%), and the Philippines (21.9%), whereas the rates were less than 10% in Japan and Australia. ESBL-producing E. coli strains were also prominent in mainland China (24.5%), Hong Kong (14.3%), and Singapore (11.3%). ESBL-producing K. oxytoca were common in the Philippines (38.5%), Singapore (33.3%), and China (30.0%). Hyperproduction of K. oxytoca chromosomal K1 beta-lactamase enzyme was common in Australia and Japan. P. mirabilis strains from Singapore produced ESBL (17.9%) despite the low prevalence (0-8.1%) in other countries. Few ESBL-producing C. koseri and Salmonella spp. strains were found in Japan, Singapore, Taiwan, and South Africa. Although there was variation among countries in substrate preference, ceftazidime was more likely to detect presumptive ESBL phenotype in K. pneumoniae and aztreonam more likely in E. coli, whereas ceftriaxone was the best substrate for the confirmation of ESBL production. ESBL-producing strains showed high levels of co-resistance to aminoglycosides, tetracycline, trimethoprim-sulfamethoxazole, and ciprofloxacin. Imipenem retained activity against all ESBL-producing strains. Organisms expressing ESBLs are widely distributed in the Asia-Pacific region, although prevalence rates vary significantly.