Aerosol Chemistry Resolved by Mass Spectrometry: Linking Field Measurements of Cloud Condensation Nuclei Activity to Organic Aerosol Composition.

Aerosol hygroscopic properties were linked to its chemical composition by using complementary online mass spectrometric techniques in a comprehensive chemical characterization study at a rural mountaintop station in central Germany in August 2012. In particular, atmospheric pressure chemical ionization mass spectrometry ((-)APCI-MS) provided measurements of organic acids, organosulfates, and nitrooxy-organosulfates in the particle phase at 1 min time resolution. Offline analysis of filter samples enabled us to determine the molecular composition of signals appearing in the online (-)APCI-MS spectra. Aerosol mass spectrometry (AMS) provided quantitative measurements of total submicrometer organics, nitrate, sulfate, and ammonium. Inorganic sulfate measurements were achieved by semionline ion chromatography and were compared to the AMS total sulfate mass. We found that up to 40% of the total sulfate mass fraction can be covalently bonded to organic molecules. This finding is supported by both on- and offline soft ionization techniques, which confirmed the presence of several organosulfates and nitrooxy-organosulfates in the particle phase. The chemical composition analysis was compared to hygroscopicity measurements derived from a cloud condensation nuclei counter. We observed that the hygroscopicity parameter (κ) that is derived from organic mass fractions determined by AMS measurements may overestimate the observed κ up to 0.2 if a high fraction of sulfate is bonded to organic molecules and little photochemical aging is exhibited.

A measurement and modelling investigation of the indoor air chemistry following cooking activities.

Domestic cooking is a source of indoor air pollutants, including volatile organic compounds (VOCs), which can impact on indoor air quality. However, the real-time VOC emissions from cooking are not well characterised, and similarly, the resulting secondary chemistry is poorly understood. Here, selected-ion flow-tube mass spectrometry (SIFT-MS) was used to monitor the real-time VOC emissions during the cooking of a scripted chicken and vegetable stir-fry meal, in a room scale, semi-realistic environment. The VOC emissions were dominated by alcohols (70% of total emission), but also contained a range of aldehydes (14%) and terpenes (5%), largely attributable to the heating of oil and the preparation and heating of spices, respectively. The direct cooking-related VOC emissions were then simulated using the Indoor Chemical Model in Python (INCHEM-Py), to investigate the resulting secondary chemistry. Modelling revealed that VOC concentrations were dominated by direct emissions, with only a small contribution from secondary products, though the secondary species were longer lived than the directly emitted species. Following cooking, hydroxyl radical concentrations reduced by 86%, while organic peroxy radical levels increased by over 700%, later forming secondary organic nitrates, peroxyacylnitrates (PANs) and formaldehyde. Monoterpene emissions were shown to drive the formation of secondary formaldehyde, albeit to produce relatively modest concentrations (average of 60 ppt). Sensitivity analysis of the simulation conditions revealed that increasing the outdoor concentrations of ozone and NOx species (2.9× and 9×, respectively) resulted in the greatest increase in secondary product formation indoors (≈400%, 200% and 600% increase in organic nitrates, PANs and formaldehyde production, respectively). Given the fact that climate change is likely to result in increased ozone concentrations in the future, and that increased window-opening in response to rising temperatures is also likely, higher concentrations of indoor oxidants are likely in homes in the future. This work, therefore, suggests that cooking could be a more important source of secondary pollutants indoors in the future.

Blockade of the acquisition, but not expression, of associative learning by pre-session intra-amygdala R(+) 7-OH-DPAT.

RATIONALE: Two issues were addressed regarding the effects of amygdala dopamine manipulations on associative learning: first, an apparent contradiction between the effects of post- vs. pre-session dopaminergic manipulations and second, the ability of dopaminergic infusions to affect association formation vs. its expression following extended training. OBJECTIVES: The ability of pre-session infusions of a dopamine receptor agonist (R(+) 7-OH-DPAT) to inhibit acquisition of a conditioned approach response was examined and compared with the same manipulation following overtraining. Further experiments extended these findings. MATERIALS AND METHODS: Experiment 1 infused pre-session intra-amygdala R(+) 7-OH-DPAT (0, 0.1, 1 nmol) during conditioned approach acquisition. Experiment 2 applied pre-session intra-amygdala R(+) 7-OH-DPAT (0, 0.01, 0.1, 1 nmol) during expression of the same response, once well learned. Experiment 3 required the inhibition of a conditioned approach response following unconditioned stimulus (US) removal. Experiment 4 examined the ability of animals with prior drug experience to acquire a conditioned response to a novel stimulus. RESULTS: Experiments 1-3 showed that pre-session amygdala R(+) 7-OH-DPAT impaired acquisition of either excitatory or inhibitory conditioned responding, but was ineffective following overtraining. Drug-induced impairments in acquisition of a specific conditioned stimulus (CS)-US relationship continued well beyond the cessation of drug treatment, but were found not to transfer to an alternate CS in Experiment 4. CONCLUSIONS: Pre-session dopamine receptor activation within the amygdala may impair the acquisition, but not expression, of CS-US associations. Enhanced learning reported earlier following post-session dopamine receptor activation may occur indirectly through reduced interference with the consolidation of recent learning.

Facilitation of appetitive pavlovian conditioning by d-amphetamine in the shell, but not the core, of the nucleus accumbens.

The effects of postsession d-amphetamine within subregions of the ventral and dorsal striatum on appetitive Pavlovian learning were assessed. Rats acquired a conditioned approach response on presentation of a stimulus predictive of 10% sucrose solution (unconditioned stimulus [US]), but not during equally frequent presentations of a stimulus uncorrelated with the US. In Experiment 1, postsession d-amphetamine infusions enhanced acquisition of conditioned responding, with no effect on control measures. In Experiment 2, rats received postsession d-amphetamine in the accumbens shell or core. Shell infusions facilitated conditioning; core infusions did not. In Experiment 3, dorsomedial striatal infusions of d-amphetamine also were ineffective. In sum, dopaminergic activation within the shell, but not the core, of the nucleus accumbens facilitates the acquisition of a Pavlovian association.

Blockade of sensitisation-induced facilitation of appetitive conditioning by post-session intra-amygdala nafadotride.

Prior D-amphetamine experience has been reported to enhance appetitive Pavlovian conditioning. The present study assessed the involvement of the mesoamygdaloid dopamine projection in this effect. Bilateral post-session intra-amygdala infusions of the D3 dopamine receptor antagonist, L-nafadotride, or vehicle were given during acquisition of a Pavlovian association in sensitised and unsensitised rats. During these sessions, subjects received presentations of a stimulus (CS(+)) paired with 10% sucrose availability. A second stimulus (CS(-)) was also presented but never paired with sucrose. Sensitised animals infused post-session with vehicle acquired a Pavlovian conditioned approach response during CS(+) presentations more rapidly than controls, as we have shown previously. However, post-session intra-amygdala L-nafadotride selectively retarded conditioned responding to the CS(+) in both groups of animals, abolishing the difference between sensitised and unsensitised rats. These results, therefore, extend the evidence for the involvement of the mesoamygdaloid dopamine projection in Pavlovian conditioning, and the facilitation of associative learning following sensitisation.

Isolation rearing-induced facilitation of Pavlovian learning: abolition by postsession intra-amygdala nafadotride.

It has been shown previously in this laboratory that rats reared in social isolation acquire a Pavlovian-conditioned approach task much more rapidly than their respective controls. This study assessed the involvement specifically of the mesoamygdaloid dopamine pathway in this facilitated learning of isolates. Thus, animals were required to associate arbitrary stimuli with a pulsed light stimulus (unconditioned stimulus, US). The US, while without biological significance, was nevertheless capable of eliciting an intrinsic and sustained alerting response. Procedures ensured that the arbitrary stimuli (tone or clicker) did not elicit a response in the first instance, and were presented either paired (CS+) or unpaired (CS-) with the US. Isolates and socially reared controls received intra-amygdala infusions of the D3 dopamine receptor antagonist, L-nafadotride, or vehicle immediately following the end of each training session. The conditioned response increased over sessions in both groups of vehicle-infused rats during presentations of the CS+ stimulus, but not CS-, and isolates acquired this association more rapidly than controls. However, acquisition of this association was abolished by postsession intra-amygdala L-nafadotride. Responding to the US was largely unaffected by drug or rearing conditions. Hence, these data provide strong evidence for the specific involvement of the mesoamygdaloid dopamine projection in the facilitation of associative learning by isolation rearing.

Effects of sensitization on the detection of an instrumental contingency.

While prior exposure to drugs of abuse permanently changes many behaviors, the underlying psychological mechanisms are relatively obscure. Here, the effects of sensitization on the detection of an action-outcome relationship were assessed, using a particularly stringent contingency degradation procedure. Rats were trained to leverpress until the probability of reinforcement for a response on one lever, or alternative reinforcement for a response on a second lever was reduced to 0.05 per second. Sensitization was then carried out (1mg/kg d-amphetamine/day for 7 days). Then, one reinforcer was also made available for a lack of response on either lever (p=0.05/s), maintaining its contiguity with the original response but eliminating its contingent relationship. Sensitized animals were more active, particularly early in the contingency degradation phase, but reduced responding directed at the degraded action-outcome contingency at a similar rate as controls. However, controls also reduced responding directed at the nondegraded contingency until very late in training, while sensitized animals maintained nondegraded responding at baseline levels. It was suggested that the relatively specific response shown by sensitized animals may reflect either improved action-outcome utilization or discrimination of relevant task features.

Effects of land use on surface-atmosphere exchanges of trace gases and energy in Borneo: comparing fluxes over oil palm plantations and a rainforest.

This paper reports measurements of land-atmosphere fluxes of sensible and latent heat, momentum, CO(2), volatile organic compounds (VOCs), NO, NO(2), N(2)O and O(3) over a 30 m high rainforest canopy and a 12 m high oil palm plantation in the same region of Sabah in Borneo between April and July 2008. The daytime maximum CO(2) flux to the two canopies differs by approximately a factor of 2, 1200 mg C m(-2) h(-1) for the oil palm and 700 mg C m(-2) h(-1) for the rainforest, with the oil palm plantation showing a substantially greater quantum efficiency. Total VOC emissions are also larger over the oil palm than over the rainforest by a factor of 3. Emissions of isoprene from the oil palm canopy represented 80 per cent of the VOC emissions and exceeded those over the rainforest in similar light and temperature conditions by on average a factor of 5. Substantial emissions of estragole (1-allyl-4-methoxybenzene) from the oil palm plantation were detected and no trace of this VOC was detected in or above the rainforest. Deposition velocities for O(3) to the rainforest were a factor of 2 larger than over oil palm. Emissions of nitrous oxide were larger from the soils of the oil palm plantation than from the soils of the rainforest by approximately 25 per cent. It is clear from the measurements that the large change in the species composition generated by replacing rainforest with oil palm leads to profound changes in the net exchange of most of the trace gases measured, and thus on the chemical composition of the boundary layer over these surfaces.

Role of the mesoamygdaloid dopamine projection in emotional learning.

RATIONALE: Amygdala dopamine is crucially involved in the acquisition of Pavlovian associations, as measured via conditioned approach to the location of the unconditioned stimulus (US). However, learning begins before skeletomotor output, so this study assessed whether amygdala dopamine is also involved in earlier 'emotional' learning. OBJECTIVES: A variant of the conditioned reinforcement (CR) procedure was validated where training was restricted to curtail the development of selective conditioned approach to the US location, and effects of amygdala dopamine manipulations before training or later CR testing assessed. METHODS: Experiment 1a presented a light paired (CS+ group) or unpaired (CS- group) with a US. There were 1, 2 or 10 sessions, 4 trials per session. Then, the US was removed, and two novel levers presented. One lever (CR+) presented the light, and lever pressing was recorded. Experiment 1b also included a tone stimulus. Experiment 2 applied intra-amygdala R(+) 7-OH-DPAT (10 nmol/1.0 microl/side) before two training sessions (Experiment 2a) or a CR session (Experiment 2b). RESULTS: For Experiments 1a and 1b, the CS+ group preferred the CR+ lever across all sessions. Conditioned alcove approach during 1 or 2 training sessions or associated CR tests was low and nonspecific. In Experiment 2a, R(+) 7-OH-DPAT before training greatly diminished lever pressing during a subsequent CR test, preferentially on the CR+ lever. For Experiment 2b, R(+) 7-OH-DPAT infusions before the CR test also reduced lever pressing. CONCLUSIONS: Manipulations of amygdala dopamine impact the earliest stage of learning in which emotional reactions may be most prevalent.

An automated analyzer to measure surface-atmosphere exchange fluxes of water soluble inorganic aerosol compounds and reactive trace gases.

Here, we present a new automated instrument for semicontinuous gradient measurements of water-soluble reactive trace gas species (NH3, HNO3, HONO, HCl, and SO2) and their related aerosol compounds (NH4+, NO3-, Cl-, SO4(2-)). Gas and aerosol samples are collected simultaneously at two heights using rotating wet-annular denuders and steam-jet aerosol collectors, respectively. Online (real-time) analysis using ion chromatography (IC) for anions and flow injection analysis (FIA) for NH4+ and NH3 provide a half-hourly averaged gas and aerosol gradients within each hour. Through the use of syringe pumps, IC preconcentration columns, and high-quality purified water, the system achieves detection limits (3sigma-definition) under field conditions of typically: 136/207,135/114, 29/ 22,119/92, and 189/159 ng m(-3) for NH3/NH4+, HNO3/NO3-, HONO/ NO2-, HCl/Cl- and SO2/SO4(2-), respectively. The instrument demonstrates very good linearity and accuracy for liquid and selected gas phase calibrations over typical ambient concentration ranges. As shown by examples from field experiments, the instrument provides sufficient precision (3-9%), even at low ambient concentrations, to resolve vertical gradients and calculate surface-atmosphere exchange fluxes undertypical meteorological conditions of the atmospheric surface layer using the aerodynamic gradient technique.