Trends in fog frequencies in the Los Angeles Basin

Data from throughout the Los Angeles area were examined to determine the horizontal distribution of dense fog (visibility < 400 m) in the region and trends over time. The relationship between the occurrence of dense fog to the phase of two atmosphere–ocean cycles: the Pacific Decadal Oscillation (PDO) measured by the PDO Index and the Southern Oscillation measured by the Southern Oscillation Index (SOI) was investigated. In addition, the influence of the urban heat island and the amount of suspended particulate matter were assessed. For the three stations that had 22 or more years of data, we examined trends and the relation to atmosphere–ocean cycles. Results show a decrease in the occurrence of very low visibilities (< 400 m) at the stations in close proximity to the Pacific Ocean, Los Angeles International Airport (LAX) and Long Beach International Airport (LGB). Occurrence of the frequency of low visibilities at these two locations was also highly correlated with the phase of the PDO. Only a weak, non-statistically significant relationship was seen with the SOI. At Burbank, a reporting station about 30 km from the ocean, no trends were noted, and there was no evidence of a correlation with either the PDO Index or the SOI. In the Los Angeles Central Business District (CBD) when comparing dense fog occurrence in the early 1960s to a similar period in the early 2000s we saw a decrease in dense fog from a mean of 10 h per year to a mean of 3 h per year. Also contributing to the decrease was decreasing particulate pollution and increased urban warming. A downward trend in particulate concentrations coupled with an upward trend in urban temperatures were associated with a decrease in dense fog occurrence at both LAX and LGB. These trends were evident for the period 1966–1997, but appear to have ended by the late 1990s.     

Towards urban water sustainability: Analyzing management transitions in Miami,Las Vegas,and Los Angeles

As climate change challenges the sustainability of existing water supplies, many cities must transition toward more sustainable water management practices to meet demand. However, scholarly knowledge of the factors that drive such transitions is lacking, in part due to the dearth of comparative analyses in the existing transitions literature. This study seeks to identify common factors associated with transitions toward sustainability in urban water systems by comparing transitions in three cases: Miami, Las Vegas, and Los Angeles. For each case, we develop a data-driven narrative that integrates case-specific contextual data with standardized, longitudinal metrics of exposures theorized to drive transition. We then compare transitions across cases, focusing on periods of accelerated change (PoACs), to decouple generic factors associated with transition from those unique to individual case contexts. From this, we develop four propositions about transitions toward sustainable urban water management. We find that concurrent exposure to water stress and heightened public attention increases the probability of a PoAC (1), while other factors commonly expected to drive transition (e.g. financial stress) are unrelated (2). Moreover, the timing of exposure alignment (3) and the relationship between exposures and transition (4) may vary according to elements of the system’s unique context, including the institutional and infrastructure design and hydro-climatic setting. These propositions, as well as the methodology used to derive them, provide a new model for future research on how cities respond to climate-driven water challenges.     

TROPOZ II: Global distributions and budgets of methane and light hydrocarbons

One hundred atmospheric samples were collected aboard the French Caravelle research aircraft, during the TROPOZ II experiment (January 1991). Tropospheric meridional distributions versus height were then derived from 70° N to 60° S and between 0.25 km and 11 km for methane, acetylene, ethane and propane. Areas of significant emissions were identified over northern latitudes with, for acetylene, maximum mixing ratios in the north (1.896 ppbv) more than 70 times higher than in background southern latitudes (0.025 ppbv). The influence of emissions from biomass burning was also obvious in the tropical boundary layer. Significant dynamic phenomena led to high mixing ratio zones above 8 or 10 km even for the most reactive hydrocarbons.For the first time, simultaneous assessment of global tropospheric contents of several light hydrocarbons was carried out. Using TROPOZ II data (January 1991) and STRATOZ III data (June 1984) collected by Rudolph (1988) during similar aircraft flights in 1988, the following tropospheric loads (in Tg-compound) were estimated, in January 1991 and June 1984, respectively: 1.1 and 0.4 for acetylene, 5.0 and 3.9 for ethane, 3.6 and 1.4 for propane and 3545 for methane in January only. According to our results, 40 to 65% of acetylene and alkanes are oxidized in the tropics. In addition, by computing the annual tropospheric sink of acetylene and alkanes, an evaluation of their annual global fluxes was performed. The figures are, in Tg-compound y^-1 with an uncertainty of 80% to an order of magnitude, based on January and June data, respectively: 10 and 6.6 for acetylene, 16.3 and 17.6 for ethane and 52.3 and 26.5 for propane.     

Hiatus of wetland methane emissions associated with recent La Niña episodes in the Asian monsoon region

The variability of methane emissions from wetlands in the tropics and northern temperate regions can explain more than 70% of the interannual variation in global wetland methane emissions, which are largely driven by climate variability. We use climate reanalysis, remote sensing wetland area dataset and simulations from 11 land models contributing to Global Methane Budget to investigate the interannual variation and anomalies of wetland methane emissions in the Asian Monsoon region. Methane emissions in this region steadily increased over 2000–2012. However, abnormally low methane emissions were found in equatorial fully humid (Af), warm temperate winter dry (Cw), and warm temperate fully humid (Cf) Asian Monsoon climate sub-regions in 2008, 2009 and 2011, respectively. These spatially-shifting low emissions occurred simultaneously with observed wetland area shrinkage due to abnormally low precipitation. Interannual variability of wetland methane emissions in Asian Monsoon region are primarily driven by South Asian Monsoon system. However, the abnormally low emissions are related to strong La Niña events, and its accompanying effect of weakened East Asian Monsoon system and eastward Western Pacific subtropical high, which drives the shifting pattern of rainfall, and thus the spatial pattern of methane emission anomalies.     

Chemical reactions and transport of alkanes and their products in the troposphere

The product distributions have been calculated for more abundant alkanes contributing most of the carbon atoms in the alkane fraction of an ambient air hydrocarbon mixture reasonably representative of U.S. emissions. The effects of ambient temperatures on product yields has been calculated for a range of temperatures from 250 to 330 K. The sensitivity of product yields to uncertainties in alkoxy radical process rate constants has been examined with emphasis on uncertainties in decomposition reactions. Chemical lifetimes are estimated at 300 K under summertime conditions for hydrocarbons and for products of alkane photooxidation in the atmosphere. The atmospheric distribution of alkanes and products is evaluated in terms of the extent to which reaction processes are likely to occur in the planetary boundary layer compared to the free troposphere.The calculations predict a substantial effect of temperature on product yields. A large decrease in alkyl nitrate yields and a smaller decrease in ketone yields occur with increasing temperature. The yields of the short-lived, more reactive aldehydes undergo substantial increases with increasing temperature. Lower yields of ketones and higher yields of aldehydes are associated with the use of higher compared to lower decomposition process rate constants. For the type of U.S. hydrocarbon mixture available from measurements, 16 oxygenated products account for more than 60% of the total alkane carbon atoms converted to products, with most of these carbon atoms accounted for by four products. The effects of increased temperature on product reactivity and radical production may also influence O₃ production.     

Carbon dioxide and methane in the Arctic atmosphere

Fifty flask air samples were taken during April 1986 from a NOAA WP-3D Orion aircraft which flew missions across a broad region of the Arctic as part of the second Arctic Gas and Aerosol Sampling Program (AGASP II). The samples were subsequently analyzed for both carbon dioxide (CO₂) and methane (CH₄). The samples were taken in well-defined layers of Arctic haze, in the background troposphere where no haze was detected, and from near the surface to the lower stratosphere. Vertical profiles were specifically measured in the vicinity of Barrow, Alaska to enable comparisons with routine surface measurements made at the NOAA/GMCC observatory. Elevated levels of both methane and carbon dioxide were found in haze layers. For samples taken in the background troposphere we found negative vertical gradients (lower concentrations aloft) for both gases. For the entire data set (including samples collected in the haze layers) we found a strong positive correlation between the methane and carbon dioxide concentrations, with a linear regression slope of 17.5 ppb CH₄/ppm CO₂, a standard error of 0.6, and a correlation coefficient (r²) of 0.95. This correlation between the two gases seen in the aircraft samples was corroborated by in situ surface measurements of these gases made at the Barrow observatory during March and April 1986. We also find a similar relationship between methane and carbon dioxide measured concurrenty for a short period in the moderately polluted urban atmosphere of Boulder, Colorado. We suggest that the strong correlation between methane and carbon dioxide concentrations reflects a common source region for both, with subsequent long-range transport of the polluted air to the Arctic.     

厄尔尼诺现象和拉尼娜现象与中高纬地区气候的关系

利用概率统计学方法,分析厄尔尼诺现象和拉尼娜现象与中高纬地区四季气温、≥10℃活动积温、初霜、终霜及降水等的关系,对短期气候预测具有较好的参考价值。     

Distribution of methane content and methane fluxes in the Sea of Japan,Sea of Okhotsk,and near-Kuril Pacific

The spatial distribution of methane content and methane fluxes in the water in the north-western part of the Sea of Japan, in the Kuril basin of the Sea of Okhotsk, and in the near-Kuril part of the Pacific Ocean is studied using the data of marine research expeditions in 2005, 2010, and 2011. The studies revealed the significant variability of the methane flux depending on the source presence and on the sea surface conditions. The high emission of methane from water to the atmosphere is registered in the areas where its concentration exceeds the equilibrium values with the atmosphere. The use of the model of computation of the fields of currents and contaminant transport for the investigated water area enabled explaining the formation of the high concentration of methane in the center of vortices in the zones of sea water convergence in the water areas under study.     

Tropospheric methane in the mid-latitudes of the Southern Hemisphere

Results of more than 800 new measurements of methane (CH₄) concentrations in the Southern Hemisphere troposphere (34–41° S, 130–150° E) are reported. These were obtained between September 1980 and March 1983 from the surface at Cape Grim, Tasmania, through the middle (3.5–5.5 km) to the upper troposphere (7–10 km). The concentration of CH₄ increased throughout the entire troposphere over the measurement period, adding further support to the view that CH₄ concentrations are currently increasing on a global scale. For data averaged vertically through the troposphere the rate of increase found was 20 ppbv/yr or 1.3%/yr at December 1981. In the surface CH₄ data a seasonal cycle with a peak to peak amplitude of approximately 28 ppbv is seen, with the minimum concentration occurring in March and the maximum in September–October. A cycle with the same phase as that seen at the surface, but with a significantly decreased amplitude, is apparent in the mid troposphere but no cycle is detected in the upper tropospheric data. The phase and amplitude of the cycle are qualitatively in agreement with the concept that the major sink for methane is oxidation by hydroxyl radicals. Also presented is evidence of a positive vertical gradient in methane, with a suggestion that the magnitude of this gradient has changed over the period of measurements.     

Surface measurements of carbon dioxide and methane at Alert during an Arctic haze event in April, 1986

Carbon dioxide (CO₂) has been measured at Alert by grab flask sampling since 1975 as part of the World Meteorological Organization's Background Air Pollution Monitoring Program. Deviations of CO₂ concentration from the mean annual cycle have previously been attributed to air masses arriving at Alert from the source regions of the industrialized parts of Europe and the Soviet Union. In situ measurements of ambient CO₂ and methane (CH₄) were made at Alert using an automated gas chromatograph, as part of the Arctic Haze Study during April 1986. The temporal behaviour of CO₂ and CH₄ during this period was found to be highly correlated with measurements of particulate sulphate and other atmospheric trace species of anthropogenic origin. Examination of calculated air mass back-trajectories provided further evidence that the observed short-term increases in CO₂ and CH₄ mixing ratios were due to long-range transport from anthropogenic source regions.     

The global distribution of methane in the troposphere

Methane has been measured in air samples collected at approximately weekly intervals at 23 globally distributed sites in the NOAA/GMCC cooperative flask sampling network. Sites range in latitude from 90° S to 76° N, and at most of these we report 2 years of data beginning in early 1983. All measurements have been made by gas chromatography with a flame ionization detector at the NOAA/GMCC laboratory in Boulder, Colorado. All air samples have been referenced to a single secondary standard of methane-in-air, ensuring a high degree of internal consistency in the data. The precision of measurements is estimated from replicate determinations on each sample as 0.2%. The latitudinal distribution of methane and the seasonal variation of this distribution in the marine boundary layer has been defined in great detail, including a remarkable uniformity in background levels of methane in the Southern Hemisphere. We report for the first time the observation of a complete seasonal cycle of methane at the South Pole. A significant vertical gradient is observed between a sea level and a high altitude site in Hawaii. Globally averaged background concentrations in the marine boundary layer have been calculated for the 2 year-period May 1983–April 1985 inclusive, from which we find an average increase of 12.8 ppb per year, or 0.78% per year when referenced to the globally averaged concentration (1625 ppb) at the mid-point of this period. We present evidence that there has been a slowing down in the methane growth rate.Presented at the Conference on the Scientific Application of Baseline Observations of Atmospheric Composition (SABOAC), Aspendale, Australia, 7–9 November 1984.     

Enhanced production of stratospheric OH from methane oxidation at elevated reactive chlorine levels in northern midlatitudes

Examination of odd-hydrogen production and loss processes in the lower stratosphere reveals that the large abundances of midlatitude ClO recently measured requires a reassessment of the OH yield from methane oxidation due to a more rapid initiation of the methane oxidation sequence by atomic chlorine. Using a steady state calculation for OH and an iterative procedure for evaluating odd-hydrogen production from the methane oxidation sequence, we demonstrate that both OH and reactive chlorine are amplified below 25 km. The amplified values of OH and ClO are found to be consistent with recent measurements of ClO concentrations and of OH column abundances.     

A smog chamber for studies of the reactions of terpenes and alkanes with ozone and OH

The design and performance of a smog chamber for the study of photochemical reactions under simulated environmental conditions is described. The chamber is thermostated for aerosol experiments, and it comprises a gas chromatographic sample enrichment system suitable for monitoring hydrocarbons at the ppbv level. By irradiating NO _x /alkane-mixtures rate constants for the reaction of OH radicals with n-alkanes are determined from n-pentane to n-hexadecane to be (k±2)/10^–12 cm³ s^–1=4.29±0.16, 6.2±0.6, 7.52 (reference value), 8.8±0.3, 10.2±0.3, 11.7±0.4, 13.7±0.3, 15.1±0.5, 17.5±0.6, 19.3±0.7, 22.3±1.0, and 25.0±1.3, respectively at 312 K. Rate constants, (k±2)/10^–17 cm³ s^–1, for the reaction of ozone with trans-2-butene (21.2±1.0), cis-3-methylpentene-(2) (47.2±1.7), cyclopentene (62.4±3.5), cyclohexene (7.8±0.5), cycloheptene (28.3±1.5), -pinene (8.6±1.3), and -pinene (1.4±0.2) are determined in the dark at 297 K using cis-2-butene (13.0) as reference standard.     

Studying methane emission in the north of Western Siberia

Methane emitted into the atmosphere from sources located in the Urengoi natural gas field is estimated from direct methane concentration measurements in the atmospheric boundary layer and modeling. The results of direct profile measurements in the summer-fall season of 2003 are generalized versus the data from the previous field studies and background monitoring of greenhouse gases in the northern polar region. The use of models for calculating the intensity of emission from sources located in the field area together with a set of methane concentration measurements at three altitudes allowed the authors to develop a method of verification of emission from a specific source, a deposit. The method estimates the emission both from part of the field area and from the whole field with an irregular distribution of the intensity of sources across the deposit area.     

Climatology of water excesses and shortages in the La Plata Basin

This study presents a multitemporal climatology of water excess and shortage during the 20th century in the La Plata Basin. The climatology is based on 0.5^o?×?0.5^o grid across the region. We transform monthly precipitation series for each point into index series at different time scales using the Standardized Precipitation Index (SPI). A month is under water excess (shortage) conditions at different time scales (i?=?6, 9, 12, and 18 months), when SPI[i](j)?>?1.5 (SPI[i](j)?<?1.5), where j is the current month. Trends in precipitation were determined using mean regional series of average values over the entire basin. A month when more than 30% of the total basin is under water excesses (shortages) is defined as an excess (shortage) critical month. From the vulnerability point of view, we analyzed the occurrence of critical months. The number of excess critical months increase with time scale of index, and almost all the critical months occurred after 1950 as a consequence of the low-frequency precipitation pattern. That means a noticeable increase in the vulnerability to extended excesses (more than 30% of the area under water excesses) after 1950, especially over the Upper Paraná and the Uruguay basins. For shortage critical months, the behavior depends on time scales. At large time scale (18 and 12 months), almost all the shortage critical months occurred in the period 1901–1950 and only at shorter time scale (9 and 6 months), some critical months appeared after 1950. That means a noteworthy decrease in the basin vulnerability to extended water shortage after 1950 and a moderate decrease in vulnerability to generalized shortage. If we analyze the frequency and mean duration of water excess and shortage events across the basin, we can appreciate that there is a tendency to relate higher frequency regions with regions with lower mean duration events, and conversely.     

Field studies of methane emission from termite nests into the atmosphere and measurements of methane uptake by tropical soils

The flux of CH₄ and CO₂ from termite nests into the atmosphere has been measured in a broad-leafed-type savannah in South Africa. Measurements were carried out on nests of species of six genera, i.e., Hodotermes, Macrotermes, Odontotermes, Trinervitermes, Cubitermes, and Amitermes. The flux rates of CH₄ relative to the flux rate of CO₂ in terms of carbon obtained for the individual species showed ratios of 2.9×10^-3, 7.0×10^-4, 6.7×10^-5, 8.7×10^-3, 2.0×10^-3 and 4.2×10^-3, respectively. Using data published on the assimulation efficiencies of termites, the flux of carbon as CH₄ accounts for 6.0×10^-5 to 2.6×10^-3 of the carbon ingested which results in a global CH₄ emission by termites of 2 to 5×10¹² g/yr. Methane is decomposed in the soil with average decomposition rates of 52 g/m²/h. The annual CH₄ consumption in the tropics and subtropics is estimated to be 21×10¹² g which exceeds the CH₄ emission rate by termites.     

Analysis of Wind Roses Using Hierarchical Cluster and Multidimensional Scaling Analysis at La Plata,Argentina

Knowledge of frequency wind patterns is very important for air pollution modelling, especially in a city like La Plata (approximately 850,000 inhabitants) with high vehicular and industrial activities and no air monitoring network. An hourly wind analysis was carried out on data from two local weather stations (points A and J). An initial result was that, in spite of differences in data quality, the local weather stations observations were consistent with local and regional National Meteorological Service (NMS) monthly based observations. Two non conventional multivariate statistical methods were employed to further analyse hourly data at points A and J. Hierarchical cluster resulted in a good summarising tool to visualise prevailing hourly winds. Resultant vectors emerging from the clustering process showed good similarity between sites and seasons; this allowed a further visualization of the average diurnal wind development. Multidimensional scaling (MDS) permitted a pairwise comparison of a large number of hourly wind roses. These wind roses were more similar to each other in colder seasons and at site A (the one that is closer to the river) than in warmer seasons and at site J. Most of the observed variations regarding seasons and sites revealed by cluster and MDS analysis are explained in terms of the sea-land breeze circulations. The methodology applied proved to be of utility for simplifying the analysis of high dimensional data with numerous observations.