Photodissociation of the CH2Br radical: A theoretical study.

Bromine atom (Br) reactions lead to ozone depletion in the troposphere and stratosphere. Photodegradation of bromocarbons is one of the main sources of bromine atoms in the atmosphere. Here, we use high-level ab initio methods, including spin-orbit effects, to study the photodissociation of the CH2Br radical. All possible fragmentation pathways, namely CH2Br + hν → CH2 + Br, HCBr + H, and CBr + H2, have been analyzed. Potential-energy curves of the ground and several excited electronic states along the corresponding dissociating bond distance of each pathway have been calculated. Considering the actinic fluxes of solar irradiation in the troposphere and in the stratosphere in the relevant range of frequencies, it is found that the first five excited states of CH2Br can be accessed from the ground state. Analysis of the potential curves shows that the pathways producing CH2 + Br and HCBr + H can proceed through a fast direct dissociation mechanism, while the pathway leading to CBr + H2 involves much slower dissociation mechanisms like internal conversion between electronic states, predissociation, or tunneling through exit barriers. The main implications are that the two faster channels are predicted to be dominant, and the slower pathway is expected to be less relevant. The tropospheric and stratospheric solar actinic fluxes also allow for further dissociation of the HCBr and CBr fragments, generating additional Br atoms, provided that they survive possible collisions with other atmospheric reagents. Finally, we discuss the possible effect of each of the three CH2Br dissociation pathways on the depletion of atmospheric ozone.

Bromine, iodine and sodium along the EAIIST traverse: Bulk and surface snow latitudinal variability.

During the East Antarctic International Ice Sheet Traverse (Eaiist, december 2019), in an unexplored part of the East Antarctic Plateau, snow samples were collected to expand our knowledge of the latitudinal variability of iodine, bromine and sodium as well as their relation in connection with emission processes and photochemical activation in this unexplored area. A total of 32 surface (0-5 cm) and 32 bulk (average of 1 m depth) samples were taken and analysed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Our results show that there is no relevant latitudinal trend for bromine and sodium. For bromine they also show that it has no significant post-depositional mechanisms while its inland surface snow concentration is influenced by spring coastal bromine explosions. Iodine concentrations are several orders of magnitude lower than bromine and sodium and they show a decreasing trend in the surface samples concentration moving southward. This suggests that other processes affect its accumulation in surface snow, probably related to the radial reduction in the ozone layer moving towards central Antarctica. Even though all iodine, bromine and sodium present similar long-range transport from the dominant coastal Antarctic sources, the annual seasonal cycle of the ozone hole over Antarctica increases the amount of UV radiation (in the 280-320 nm range) reaching the surface, thereby affecting the surface snow photoactivation of iodine. A comparison between the bulk and surface samples supports the conclusion that iodine undergoes spring and summer snow recycling that increases its atmospheric lifetime, while it tends to accumulate during the winter months when photochemistry ceases.

Recent and historical pollution legacy in high altitude Lake Marboré (Central Pyrenees): A record of mining and smelting since pre-Roman times in the Iberian Peninsula.

We have analyzed potential harmful trace elements (PHTE; Pb, Hg, Zn, As and Cu) on sediment cores retrieved from lake Marboré (LM) (2612 m a.s.l, 42°41'N; 0° 2'E). PHTE variability allowed us to reconstruct the timing and magnitude of trace metal pollutants fluxes over the last 3000 years in the Central Pyrenees. A statistical treatment of the dataset (PCA) enabled us to discern the depositional processes of PHTE, that reach the lake via direct atmospheric deposition. Indeed, the location of LM above the atmospheric boundary layer makes this lake an exceptional site to record the long-range transport of atmospheric pollutants in the free troposphere. Air masses back-trajectories analyses enabled us to understand the transport pathways of atmospheric pollutants while lead isotopic analyses contributed to evaluate the source areas of metal pollution in SW Europe during the Late Holocene. PHTE variability, shows a clear agreement with the main exploitation phases of metal resources in Southern Europe during the Pre-Industrial Period. We observed an abrupt lead enrichment from 20 to 375 yrs CE mostly associated to silver and lead mining and smelting practices in Southern Iberia during the Roman Empire. This geochemical data suggests that regional atmospheric metal pollution during the Roman times rivalled the Industrial Period. PHTE also increased during the High and Late Middle Ages (10-15th centuries) associated to a reactivation of mining and metallurgy activities in high altitude Pyrenean mining sites during climate amelioration phases. Atmospheric mercury deposition in the Lake Marboré record mostly reflects global emissions, particularly from Almadén mines (central Spain) and slightly fluctuates during the last three millennia with a significant increase during the last five centuries. Our findings reveal a strong mining-related pollution legacy in alpine lakes and watersheds that needs to be considered in management plans for mountain ecosystems as global warming and human pressure effects may contribute to their future degradation.

Recent increase in NO2 levels in the southeast of the Iberian Peninsula.

We report the evolution of tropospheric NO2 over the south-east of the Iberian Peninsula from 2005 to 2017. We have used hourly NO2 levels measured at air-quality stations in urban and suburban environments. Annual averages ranged between 14 and 45 µg m-3, with peaks above 200 µg m-3. A monthly variation was observed, with higher concentrations in cold months (40-60 µg m-3) and lower levels in the warm season (13-17 µg m-3). A diurnal pattern was found in urban and suburban areas. The upward trend in NO2 observed during the whole period contrasts with the upward trend reported in 2013-2017. The NO2 tropospheric column levels measured by the Ozone Monitoring Instrument over the Iberian Peninsula indicated a similar behaviour; nevertheless, the largest Spanish metropolitan areas did not show this increase. The mean sea level pressure and wind field data of ERA5 (European Centre for Medium-Range Weather Forecasts) were used to investigate the weather conditions, the NO2 outputs of the Copernicus Monitoring Services being used for the assessment of the NO2 spatial distribution. NO2 regional events, with concentrations in the range 140-150 µg m-3, and which occurred both in the winter and summer season under anticyclonic conditions, are also described. A local origin is identified in winter, whereas in summer, they are associated with a high-pressure system that blocks Mediterranean outflows towards the Atlantic Ocean. The high NO2 levels are attributed mainly to two factors: i) local emissions, rather than contributions from the western Mediterranean (or even North Africa), and ii) an increase in the pressure gradient between the Atlantic and the Mediterranean pressure systems, associated with a decrease in wind speed, was found during the last five years compared with the previous eight. Meteorological and chemical changes in mid-latitudes associated with global warming should also be investigated in the future.

Unexpected increase in the oxidation capacity of the urban atmosphere of Madrid, Spain.

Atmospheric oxidants such as ozone (O3), hydroxyl and nitrate radicals (OH and NO3) determine the ability of the urban atmosphere to process organic and inorganic pollutants, which have an impact on air quality, environmental health and climate. Madrid city has experienced an increase of 30-40% in ambient air O3 levels, along with a decrease of 20-40% in NO2, from 2007 to 2014. Using air pollution observations and a high-resolution air quality model, we find a large concentration increase of up to 70% and 90% in OH and NO3, respectively, in downtown Madrid (domain-wide average increase of 10% and 32% for OH and NO3, respectively). The results also show an 11% reduction in the nitric acid concentrations, leading to a remarkable denoxification of this urban atmosphere with implications for lower PM2.5 levels and nitrogen input into ecosystems. This study suggests that projected worldwide NOx emission reductions, following air quality standards, will lead to important changes in the oxidizing capacity of the atmosphere in and around large cities.

Utility of the HIV dementia scale in assessing risk for significant HIV-related cognitive-motor deficits in a high-risk urban adult sample.

Considerable literature reflects the range of HIV-related neurocognitive complications, including relatively poor performance on tests of: movement and coordination; attention and concentration; reaction time; and mental flexibility. Efforts to develop appropriate screening techniques include the HIV Dementia Scale (HDS), a brief measure that has demonstrated promise but is lacking extensive independent evaluation. The present study examines the utility of the HDS in a sample of HIV-seropositive adults with a co-morbid history of psychiatric and substance use disorders. Forty subjects (65% male; mean age 41 years; mean education 12.2 years; 55% African American, 30% Caucasian) recruited for a study of the impact of brief psychotherapy on adherence to medications and medical appointments, relapse prevention, and/or enhancement of mental health functioning completed a battery of neuropsychological measures, including the HDS. Forty percent were identified as at high risk for significant cognitive-motor disorder (HDS total score < or =10). After controlling for age, education, illness (absolute CD4), and depressed mood, high-risk participants performed significantly worse on measures of simple and sustained divided attention, psychomotor speed, and working memory. However, only 25 of 40 (63%) were correctly classified based on their performance on traditional tests of neuropsychological functioning. Implications and limitations of the study are discussed.

Diet and estrous cycle influence pain sensitivity in rats.

Effects of estrous cycle and acute and chronic access to palatable fluids on tail-flick latency and opiate-induced analgesia were assessed in 124 female Long Evans rats. Following three consistent cycles, rats were water deprived for 8 h and then given ad lib access to 20 ml of either water, a 32% sucrose solution, or corn oil for 5 h. Nociceptive testing was conducted immediately preceding and 30, 60, and 90 min following an SC injection of morphine sulfate (7.5 mg/kg). Diestrus rats had prolonged premorphine tail-flick latencies compared to rats in proestrus. Rats that consumed corn oil had longer tail-flick latencies preceding and 30 min following morphine injections than rats that drank water or the sucrose solution. Rats were retested after they had ad lib access to the same fluid for 3 weeks. No estrous cycle differences were noted following chronic consumption. Rats with chronic access to sucrose showed increased baseline pain sensitivity and increased morphine-induced analgesia at 30, 60, and 90 min postinjection. These data support the notion that palatable fluid consumption attenuates estrous cycle-dependent differences in pain sensitivity.