Sensitive Parameters -[368 refs.]. -(DEGUILLAUME*, L.; LERICHE, M.; DESBOEUFS, K.; MAILHOT, G.; GEORGE, C.; CHAUMERLIAC, N.; Chem. Rev. (Washington, D. C.) 105 (2005) 9, 3388-3431; Lab. Meteorol. Phys., Univ. Blaise Pascal, F-63177 Aubiere, Fr.; Eng.) -Schramke 49-218

Three experiments examined the effect on reasoning of the degree of belief in the premises. In Expt 1,84 adult participants had to evaluate their degree of confidence in the truth of conditional statements, and to evaluate the conclusion of modusponens (MP) arguments using these statements as the major premise. The same seven-point response format was used for both tasks. In the inference task, 48 per cent of the participants accepted all the MP arguments even when they disagreed with their major premise. The other participants considered that some or all of the conclusions were not certainly true. Moreover, they assigned a degree of belief to each conclusion which was highly correlated with the one they attributed to the major premise. Thus two modes of responding emerged, one which assumed the truth of the premises irrespective of actual beliefs about them, and one which integrated the truth status given to the premises. In Expt 2, one replication and three controls confirmed that non-endorsement of the MP arguments was due to the lack of believability of the premises. In Expt 3, on the usual three-response format, 80 adults were invited to adopt one of these two responding modes with four MP arguments, and then to shift to the other one with a new set of four MP arguments.With the appropriate instructions, assumption-based responding was adopted by only 43 per cent of the participants, and belief-based responding by 98 per cent. Three hypotheses are considered about the second mode of responding.The major theories of reasoning with deductive arguments are restricted to situations where individuals are assumed to endorse the truth of the premises while they infer a conclusion (Braine, 1990; Johnson-Laird & Byrne, 1991 ; Rips, 1983). In order for this restriction to hold, some precautions are usually taken to avoid having participants question the truth of the premises. However, these precautions do not necessarily guarantee that participants will actually comply with the expectations of the experimenter. The grounds for suspicion are particularly high in situations where the premises contradict individuals' beliefs. Thus two questions need to be examined: do participants really endorse the premises when they have reason not to do so? If they do not endorse the premises, what kind of reasoning do they employ?Two precautions are usually taken in order to ensure that participants endorse the truth of the premise. The first is use of premises which cannot interact with beliefs because they are abstract, or because they refer to imaginary situations or to situations outside the knowledge domain of the participants. The second precaution is to instruct participants to assume that the premises are true. If participants actually * Requests for reprints.

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Halogen atoms affect the budget of ozone and the fate of pollutants such as hydrocarbons and mercury. Yet their sources and significances in polluted continental regions are poorly understood. Here we report the observation of unprecedented levels (averaging to 60 parts per trillion) of bromine chloride (BrCl) at a mid-latitude site in North China during winter. Widespread coal burning in rural households and a photo-assisted process were the primary source of BrCl and other bromine gases. BrCl contributed about 55% of both bromine (Br) and chlorine (Cl) atoms. The halogen atoms increased the abundance of ‘conventional’ tropospheric oxidants (OH, HO2, and RO2) by 26–73%, and enhanced oxidation of hydrocarbon by nearly a factor of two and the net ozone production by 55%. Our study reveals the significant role of reactive halogen in winter atmospheric chemistry and the deterioration of air quality in continental regions where uncontrolled coal combustion is prevalent.

Organic peroxy radicals (RO2) play a pivotal role in the degradation of hydrocarbons. The autoxidation of atmospheric RO2 radicals produces highly oxygenated organic molecules (HOMs), including low-volatility ROOR dimers formed by bimolecular RO2 + RO2 reactions. HOMs can initiate and greatly contribute to the formation and growth of atmospheric particles. As a result, HOMs have far-reaching health and climate implications. Nevertheless, the structures and formation mechanism of RO2 radicals and HOMs remain elusive. Here, we present the in-situ characterization of RO2 and dimer structure in the gas-phase, using online tandem mass spectrometry analyses. In this study, we constrain the structures and formation pathway of several HOM-RO2 radicals and dimers produced from monoterpene ozonolysis, a prominent atmospheric oxidation process. In addition to providing insights into atmospheric HOM chemistry, this study debuts online tandem MS analyses as a unique approach for the chemical characterization of reactive compounds, e.g., organic radicals.

The composition of organic aerosol has a pivotal influence on aerosol properties such as toxicity, and cloud droplets formation capability, which could affect both climate and air quality. However, a comprehensive and fundamental understanding of the chemical and physical processes that occur in nanometre-sized atmospheric particles remains a challenge that severely limits the quantification and predictive capabilities of aerosol formation pathways. Here, we investigated the effects of a fundamental and hitherto unconsidered physical property of nanoparticlesthe Laplace pressure. By studying the reaction of glyoxal with ammonium sulphate, both ubiquitous and important atmospheric constituents, we show that high pressure can significantly affect the chemical processes that occur in atmospheric ultrafine particles (i.e., particles < 100 nm). Using high-resolution mass spectrometry and UV/Vis spectroscopy, we demonstrated that the formation of reaction products is strongly (i.e., up to a factor of 2) slowed down under high pressures typical of atmospheric nanoparticles. A size-dependent relative rate constant is determined and numerical simulations illustrate the reduction in the production of the main glyoxal reaction products. These results established that the high pressure inside nanometre-sized aerosols must be considered as a key property that significantly impacts chemical processes that govern atmospheric aerosol growth and evolution. Short SynopsisHigh pressure reached inside atmospheric nanometre-sized particles affects their chemistry and therefore their formation and growth.

Heterogeneous reactions of NO2 on different surfaces play an important role in atmospheric NOx removal and HONO formation, having profound impacts on photochemistry in polluted urban areas. Previous studies have suggested that the NO2 uptake on the ground or aerosol surfaces could be a dominant source for elevated HONO during daytime. However, the uptake behavior of NO2 varies with different surfaces, and different uptake coefficients were used or derived in different studies. To obtain a more holistic picture of heterogeneous NO2 uptake on different surfaces, a series of laboratory experiments using different flow tube reactors was conducted, and the NO2 uptake coefficient (γ) were determined on inorganic particles, sea water and urban grime. The results showed that heterogeneous reactions on those surfaces were generally weak in dark condition, with the measured γ varied from <10 -8 to 3.2×10 -7 under different humidity.A photo-enhanced uptake of NO2 on urban grime were observed, with obvious formation of HONO and NO from the heterogeneous reaction. The photo-enhanced γ was measured to be 1.9×10 -6 to at 5% RH and 5.8×10 -6 at 70% RH on urban grime, showing a positive RH dependence for both NO2 uptake and HONO formation. The results demonstrate an important role of urban grime in the daytime NO2-to-HONO conversion, and could be helpful to explain the unknown daytime HONO source in the polluted urban area.

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