PCDD/F,PCB, HxCBz,PAH, and PM emission factors for fireplace and woodstove combustion in the San Francisco Bay region

Emissions from residential fireplace and woodstove appliances burning fuels available from the San Francisco Bay area were sampled for polychlorinated dibenzodioxins and dibenzofurans (PCDDs/Fs), polychlorinated biphenyls (PCBs), hexachlorobenzene (HxCBz), particulate matter (PM), polycyclic aromatic hydrocarbons (PAHs), oxygenated PAHs, and the monosaccharide levoglucosan. Emission factors for these pollutants were determined, the first known characterization of this extent. Common California natural firewoods and manufactured artificial logs were tested under operating conditions intended to reflect domestic use patterns in the Bay area, which are primarily episodic burning for aesthetic reasons. Emission factors were determined by fuel type, fuel weight, mass emission rates, and energy output, highlighting differences between fuel and combustion facility type. Average PCDD/F emissions factors ranged from 0.25 to 1.4 ng toxic equivalency (TEQ)/kg of wood burned for natural wood fuels and 2.4 ng TEQ/kg for artificial logs. The natural wood emission factors are slightly lower than those which had been estimated for the U.S. inventory. Background-corrected PCBs emitted from woodstove/oak combustion (8370 ng/kg) are 3 orders of magnitude higher in mass than total PCDDs/Fs; however, their toxicity (0.014 ng TEQ/kg) is significantly lower. HxCBz emission factors varied from 13 to 990 ng/kg and were likely fuel- and appliance-specific. Relative PAH concentrations of particle-phase compounds and emission factors were consistent with others' findings. A total of 32 PAH compounds, ranging in concentration from 0.06 to 7 mg/kg, amounted to between 0.12 and 0.38% of the PM mass, depending on the wood and facility type. Preliminary analyses suggest relationships between wood combustion markers and PCDD/F levels.     

Semivolatile and volatile organic compound emissions from wood-fired hydronic heaters

Emissions including polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), polyaromatic hydrocarbons (PAHs), and volatile organic compounds (VOCs), were sampled from different wood-fired hydronic heater (HH) technologies. Four commercially available HH technologies were studied: a single-stage conventional combustor with natural updraft, a three-stage downdraft combustion system, a bottom-fed pellet burner, and a two-stage heater with both a combustion and gasification chamber. The fuel consisted of three wood types (red oak, white pine, and white ash), one hardwood pellet brand, and one fuel mixture containing 95% red oak and 5% residential refuse by weight. The various HHs and fuel combinations were tested in a realistic homeowner fuel-charging scenario. Differences in emission levels were found between HH technologies and fuel types. PCDD/PCDF emissions ranged from 0.004 to 0.098 ng toxic equivalency/MJ(input) and PAHs from 0.49 to 54 mg/MJ(input). The former was increased by the presence of 5% by weight refuse. The white pine fuel had the highest PAH emission factor, while the bottom fed pellet burner had the lowest. The major VOCs emitted were benzene, acetylene, and propylene. The highest emissions of PAHs, VOCs, and PCDDs/PCDFs were observed with the conventional unit, likely due to the rapid changes in combustion conditions effected by the damper opening and closing.     

Near-real-time combustion monitoring for PCDD/PCDF indicators by GC-REMPI-TOFMS

The boiler exit flue gas of a municipal waste combustor was sampled to evaluate an online monitoring system for chlorobenzene congeners as indicators of polychlorinated dibenzodioxin and dibenzofuran (PCDD/PCDF) concentrations. Continuous measurements of chlorobenzene congeners using gas chromatography coupled to a resonance-enhanced multiphoton ionization - time-of-flight mass spectrometry (GC-REMPI-TOFMS) system were compared over 5-min periods with conventional sampling methods for PCDD/PCDF. Three pairs of values were taken every hour over a period of three days to characterize the combustor's response to transient operating conditions (shutdowns and startups). Isolation of specific chlorobenzene congeners from other same-mass compounds was accomplished by using a GC column separator ahead of the REMPI-TOFMS. The 50-fold variation of PCDD/PCDF concentration was paralleled by similar changes in monitored compounds of 1,4-dichlorobenzene, 1,2,4-trichlorobenzene, 1,2,3-trichlorobenzene, and 1,2,4,5-tetrachlorobenzene. A correlation of R = 0.85 and 0.89 was established between 40 pairs of simultaneous 5-min GC-REMPI-TOFMS measurements of 1,2,4-trichlorobenzene and 5 min conventional sampling and analysis for the TEQ and Total measures of PCDD/PCDF, respectively. The GC-REMPI-TOFMS system can be used to provide frequent measures of correlative PCDD/PCDF concentration thereby allowing for an understanding of measures to minimize PCDD/PCDF formation and develop operational feedback to limit emissions.     

Cognitive interviewing procedures and suggestibility in children's recall

In this study the authors examine the effects of procedures adapted from the cognitive interview of R. E. Geiselman, R.P. Fisher, D.P. MacKinnon, and H.L. Holland (1985) on children's recall following exposure to misleading suggestions. Children aged 5-7 years and 9-11 years saw a videotaped story and were presented with misleading or neutral information concerning story details. All were later given free- and cued-recall tests preceded by standard interview instructions or instructions that reinstated the encoding context and encouraged exhaustive reporting. Increased recall accuracy was found following cognitive interview instructions. Both age groups were susceptible to misleading suggestions, but susceptibility was unaffected by interview type. The authors discuss the implications for interviewing child witnesses.     

连续生产1,1,1,3,3,3—六氟丙烷和1—氯—1,1,3,3,3—五氟丙烷的工艺

介绍了在液相中连续生产１,１,１,３,３,３,－六氟丙烷（ＨＦＣ２３６ｆａ）和／或１－氯－１,１,３,３,３－五氟内烷（ＨＣＦＣ２３５ｆａ）的工艺,反应中使用ＨＣＦＣ－２３５ｆａ和／或ＨＦＣ２３６ｆａ作为溶剂。当反应是在ＳｂＦ３、ＳｂＦ５或ＳｂＦ５和ＨＳＯ３Ｆ的混合物催化剂存在下进行时,反应物料对所用容器的腐蚀非常低。     

Sulfur coating of urea treated with attapulgite clay

A commercial attapulgite-type gelling clay was added as a conditioning-hardening agent to urea which was then tested as a substrate for sulfur coating. The coating tests were made in bench-scale batch equipment. The total coating weights and the 7-day dissolution rates of the sulfur-coated products were determined and compared with those from similar tests of previously made sulfur-coated urea products containing calcium lignosulfonate or formaldehyde. Compared with urea substrates containing formaldehyde, the urea containing attapulgite clay required about one-third less sulfur coating to attain the same 7-day dissolution rate. The urea containing attapulgite clay and the urea containing calcium lignosulfonate were about equally effective as substrates for sulfur coating.     

Influence of the number of questions on the student''s achievement in tests of anatomy

The authors compare student's achievement in tests with low and moderately high number of questions requiring short answers. Five groups of Medical School students underwent their regular Anatomy evaluation tests, which consisted of 13 questions (one group), 15 (two groups) and 25 (two groups). In each group five questions were chosen at random, average scores being calculated from their marks. These scores were statistically compared to the ones calculated from the marks given to the full-length evaluation tests; it became quite evidente that averages go up when the number of questions is increased. Putting the averages in terms of A, B, C and D scores (very good, good, regular and insufficient), it was noted that failure to reach at least the C score is inversely proportional to the number of questions. The results are discussed in terms of determining the most proper number of questions to be given in a test.