Air pollution is growing fastest in monsoon-affected South Asia. During the dry winter monsoon, the fumes disperse toward the Indian Ocean, creating a vast pollution haze, but their fate during the ...wet summer monsoon has been unclear. We performed atmospheric chemistry measurements by aircraft in the Oxidation Mechanism Observations campaign, sampling the summer monsoon outflow in the upper troposphere between the Mediterranean and the Indian Ocean. The measurements, supported by model calculations, show that the monsoon sustains a remarkably efficient cleansing mechanism by which contaminants are rapidly oxidized and deposited to Earth's surface. However, some pollutants are lofted above the monsoon clouds and chemically processed in a reactive reservoir before being redistributed globally, including to the stratosphere.
Significance Secondary production is the formation of new animal biomass from growth for all individuals in a given area during some period of time. It can be a powerful tool for evaluating ecosystem ...function because it incorporates multiple characteristics of a population or community of organisms such as density, body size, growth, and survivorship into a single metric. Here, we find that fish communities living on the complex hardscape habitat created throughout the water column by the structure of oil and gas platforms off California have the highest secondary production per unit area of seafloor of any marine ecosystem for which similar estimates exist.
Secondary (i.e., heterotrophic or animal) production is a main pathway of energy flow through an ecosystem as it makes energy available to consumers, including humans. Its estimation can play a valuable role in the examination of linkages between ecosystem functions and services. We found that oil and gas platforms off the coast of California have the highest secondary fish production per unit area of seafloor of any marine habitat that has been studied, about an order of magnitude higher than fish communities from other marine ecosystems. Most previous estimates have come from estuarine environments, generally regarded as one of the most productive ecosystems globally. High rates of fish production on these platforms ultimately result from high levels of recruitment and the subsequent growth of primarily rockfish (genus Sebastes ) larvae and pelagic juveniles to the substantial amount of complex hardscape habitat created by the platform structure distributed throughout the water column. The platforms have a high ratio of structural surface area to seafloor surface area, resulting in large amounts of habitat for juvenile and adult demersal fishes over a relatively small footprint of seafloor. Understanding the biological implications of these structures will inform policy related to the decommissioning of existing (e.g., oil and gas platforms) and implementation of emerging (e.g., wind, marine hydrokinetic) energy technologies.
Enhanced tropospheric trace gases such as CO, CH4 and H2O and reduced stratospheric O3 were measured in situ in the lowermost stratosphere over northern Europe on 26 September 2012 during the TACTS ...aircraft campaign. The measurements indicate that these air masses clearly differ from the stratospheric background. The calculation of 40-day backward trajectories with the trajectory module of the CLaMS model shows that these air masses are affected by the Asian monsoon anticyclone. Some air masses originate from the boundary layer in Southeast Asia/West Pacific and are rapidly lifted (1–2 days) within a typhoon up to the outer edge of the Asian monsoon anticyclone. Afterwards, the air parcels are entrained by the anticyclonic circulation of the Asian monsoon. The subsequent long-range transport (8–14 days) of enhanced water vapour and pollutants to the lowermost stratosphere in northern Europe is driven by eastward transport of tropospheric air from the Asian monsoon anticyclone caused by an eddy shedding event. We found that the combination of rapid uplift by a typhoon and eastward eddy shedding from the Asian monsoon anticyclone is a novel fast transport pathway that may carry boundary emissions from Southeast Asia/West Pacific within approximately 5 weeks to the lowermost stratosphere in northern Europe.
Emissions of volatile organic compounds (VOCs) associated with oil and natural gas production in the Uintah Basin, Utah were measured at a ground site in Horse Pool and from a NOAA mobile laboratory ...with PTR-MS instruments. The VOC compositions in the vicinity of individual gas and oil wells and other point sources such as evaporation ponds, compressor stations and injection wells are compared to the measurements at Horse Pool. High mixing ratios of aromatics, alkanes, cycloalkanes and methanol were observed for extended periods of time and for short-term spikes caused by local point sources. The mixing ratios during the time the mobile laboratory spent on the well pads were averaged. High mixing ratios were found close to all point sources, but gas well pads with collection and dehydration on the well pad were clearly associated with higher mixing ratios than other wells. The comparison of the VOC composition of the emissions from the oil and natural gas well pads showed that gas well pads without dehydration on the well pad compared well with the majority of the data at Horse Pool, and that oil well pads compared well with the rest of the ground site data. Oil well pads on average emit heavier compounds than gas well pads. The mobile laboratory measurements confirm the results from an emissions inventory: the main VOC source categories from individual point sources are dehydrators, oil and condensate tank flashing and pneumatic devices and pumps. Raw natural gas is emitted from the pneumatic devices and pumps and heavier VOC mixes from the tank flashings.
When oil and gas platforms become obsolete they go through a decommissioning process. This may include partial removal (from the surface to 26 m depth) or complete removal of the platform structure. ...While complete removal would likely eliminate most of the existing fish biomass and associated secondary production, we find that the potential impacts of partial removal would likely be limited on all but one platform off the coast of California. On average 80% of fish biomass and 86% of secondary fish production would be retained after partial removal, with above 90% retention expected for both metrics on many platforms. Partial removal would likely result in the loss of fish biomass and production for species typically found residing in the shallow portions of the platform structure. However, these fishes generally represent a small proportion of the fishes associated with these platforms. More characteristic of platform fauna are the primarily deeper-dwelling rockfishes (genus Sebastes). "Shell mounds" are biogenic reefs that surround some of these platforms resulting from an accumulation of mollusk shells that have fallen from the shallow areas of the platforms mostly above the depth of partial removal. We found that shell mounds are moderately productive fish habitats, similar to or greater than natural rocky reefs in the region at comparable depths. The complexity and areal extent of these biogenic habitats, and the associated fish biomass and production, will likely be reduced after either partial or complete platform removal. Habitat augmentation by placing the partially removed platform superstructure or some other additional habitat enrichment material (e.g., rock boulders) on the seafloor adjacent to the base of partially removed platforms provides additional options to enhance fish production, potentially mitigating reductions in shell mound habitat.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We report an improved measurement of the cosmic microwave background B-mode polarization power spectrum with the Polarbear experiment at 150 GHz. By adding new data collected during the second season ...of observations (2013-2014) to re-analyzed data from the first season (2012-2013), we have reduced twofold the band-power uncertainties. The band powers are reported over angular multipoles , where the dominant B-mode signal is expected to be due to the gravitational lensing of E-modes. We reject the null hypothesis of no B-mode polarization at a confidence of 3.1 including both statistical and systematic uncertainties. We test the consistency of the measured B-modes with the Λ Cold Dark Matter (ΛCDM) framework by fitting for a single lensing amplitude parameter AL relative to the Planck 2015 best-fit model prediction. We obtain 0.14(foreground) 0.04(multi), where is the fiducial ΛCDM value.
Odor regulations typically specify the use of dynamic dilution olfactometery (DDO) as a method to quantify odor emissions, and Tedlar bags are the preferred holding container for grab samples. This ...study was conducted to determine if Tedlar bags affect the integrity of sampled air from animal operations. Air samples were collected simultaneously in both Tedlar bags and Tenax thermal desorption tubes. Sample sources originated from either a hydrocarbon-free air tank, dynamic headspace chamber (DHC), or swine-production facility, and were analyzed by gas chromatography-mass spectrometry-olfactometry (GC-MS-O). Several background contaminants were identified from Tedlar bags, which included the odorous compounds N, N-dimethyl acetamide (DMAC), acetic acid, and phenol. Samples from the DHC demonstrated that recovery of malodor compounds was dependent on residence time in the Tedlar bag with longer residence time leading to lower recovery. After 24 h of storage, recovery of C3-C6 volatile fatty acids (VFA) averaged 64%, 4-methylphenol and 4-ethylphenol averaged 10%, and indole and 3-methylindole were below the detection limits of GC-MS-O. The odor activity value (OAV) of grab samples collected in Tedlar bags were 33 to 65% lower following 24 h of storage. These results indicate that significant odorant bias occurs when using Tedlar bags for the sampling of odors from animal production facilities.
A commercially available dry chemiluminescence (CI) instrument for fast and precise measurement of ozone (O3) is specified. The sensitivity is ~9000 counts s−1 per ppbv of ozone. Its precision is ...entirely determined by the number of photons reaching the detector (being a photomultiplier), i.e. is quantum-noise limited. The relative precision (ΔO3/O3 in %) thus follows Poisson statistics and scales with the square root of the measurement frequency f and with the inverse O3 mixing ratio: ΔO3/O3 ∝ f0.5 · O3−0.5. At typical O3 mixing ratios between 10 and 100 ppbv (and 1 bar), the precision is 0.3–1.0% at f = 10 Hz. The maximum measurement frequency is 50 Hz. The mechanical and electronic set-up as well as the instrument performance is described. Recommendations on the adequate inlet tube configuration (inlet tube length, sampling flow) and on the way of calibration at stationary ground-based platforms and onboard aircraft are given.
We present variations of methyl chloride (CH3Cl) and nitrous oxide (N2O) in the lowermost stratosphere (LMS) obtained from air samples collected by the In‐service Aircraft for a Global Observing ...System‐Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container (IAGOS‐CARIBIC) passenger aircraft observatory for the period 2008–2012. To correct for the temporal increase of atmospheric N2O, the CARIBIC N2O data are expressed as deviations from the long‐term trend at the northern hemispheric baseline station Mauna Loa, Hawaii (ΔN2O). ΔN2O undergoes a pronounced seasonal variation in the LMS with a minimum in spring. The amplitude increases going deeper in the LMS (up to potential temperature of 40 K above the thermal tropopause), as a result of the seasonally varying subsidence of air from the stratospheric overworld. Seasonal variation of CH3Cl above the tropopause is similar in phase to that of ΔN2O. Significant correlations are found between CH3Cl and ΔN2O in the LMS from winter to early summer, both being affected by mixing between stratospheric air and upper tropospheric air. This correlation, however, disappears in late summer to autumn. The slope of the CH3Cl‐ΔN2O correlation observed in the LMS allows us to determine the stratospheric lifetime of CH3Cl to be 35 ± 7 years. Finally, we examine the partitioning of stratospheric air and tropical/extratropical tropospheric air in the LMS based on a mass balance approach using ΔN2O and CH3Cl. This analysis clearly indicates efficient inflow of tropical tropospheric air into the LMS in summer and demonstrates the usefulness of CH3Cl as a tracer of tropical tropospheric air.
Key Points
Variations of CH3Cl and N2O in the LMS observed by CARIBIC are presented
Stratospheric lifetime of CH3Cl is estimated based on the correlation between CH3Cl and N2O
Partitioning of stratospheric and tropical/extratropical tropospheric air in the LMS is examined
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