Vallée de San Joaquin | EPFL Graph Search

thumb|Vallée de San Joaquin dans la Vallée Centrale. La vallée de San Joaquin est la région de la Vallée Centrale de l'État de Californie aux États-Unis qui s'étend au sud du delta du Sacramento à Stockton. Bien que la plus grande partie de la vallée soit rurale, elle contient aussi des centres urbains importants, comme Stockton, Fresno, Modesto, Visalia et Bakersfield. C'est l'un des greniers des États-Unis, produisant 50 % des fruits et légumes et 90 % des amandes, artichauts, avocats et tomates des États-Unis. Production agricole L'amande est le premier produit d'exportation agricole de la Californie, qui produirait près de 80 % des amandes dans le monde. Ce chiffre est néanmoins revu à la baisse depuis 2010, du fait des graves problèmes environnementaux liés à la pollution que connaît la région, et au syndrome d'effondrement des colonies d'abeilles. Car à elle seule, la pollinisation des champs d'amandiers nécessite ruches, ce qui en fait la plus grande transhumance d

The 2010 California Research at the Nexus of Air Quality and Climate Change (CalNex) field study

Athanasios Nenes

The California Research at the Nexus of Air Quality and Climate Change (CalNex) field study was conducted throughout California in May, June, and July of 2010. The study was organized to address issues simultaneously relevant to atmospheric pollution and climate change, including (1) emission inventory assessment, (2) atmospheric transport and dispersion, (3) atmospheric chemical processing, and (4) cloud-aerosol interactions and aerosol radiative effects. Measurements from networks of ground sites, a research ship, tall towers, balloon-borne ozonesondes, multiple aircraft, and satellites provided in situ and remotely sensed data on trace pollutant and greenhouse gas concentrations, aerosol chemical composition and microphysical properties, cloud microphysics, and meteorological parameters. This overview report provides operational information for the variety of sites, platforms, and measurements, their joint deployment strategy, and summarizes findings that have resulted from the collaborative analyses of the CalNex field study. Climate-relevant findings from CalNex include that leakage from natural gas infrastructure may account for the excess of observed methane over emission estimates in Los Angeles. Air-quality relevant findings include the following: mobile fleet VOC significantly declines, and NOx emissions continue to have an impact on ozone in the Los Angeles basin; the relative contributions of diesel and gasoline emission to secondary organic aerosol are not fully understood; and nighttime NO3 chemistry contributes significantly to secondary organic aerosol mass in the San Joaquin Valley. Findings simultaneously relevant to climate and air quality include the following: marine vessel emissions changes due to fuel sulfur and speed controls result in a net warming effect but have substantial positive impacts on local air quality. © 2013. American Geophysical Union. All Rights Reserved.

Blackwell Publishing Ltd2013

Comprehensive airborne characterization of aerosol from a major bovine source

Athanasios Nenes

We report an extensive airborne characterization of aerosol downwind of a massive bovine source in the San Joaquin Valley (California) on two flights during July 2007. The Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter probed chemical composition, particle size distribution, mixing state, sub- and supersaturated water uptake behavior, light scattering properties, and the interrelationship between these parameters and meteorology. Total PM1.0 levels and concentrations of organics, nitrate, and ammonium were enhanced in the plume from the source as compared to the background aerosol. Organics dominated the plume aerosol mass (∼56ĝ€"64%), followed either by sulfate or nitrate, and then ammonium. Particulate amines were detected in the plume aerosol by a particle-into-liquid sampler (PILS) and via mass spectral markers in the Aerodyne C-ToF-AMS. Amines were found to be a significant atmospheric base even in the presence of ammonia; particulate amine concentrations are estimated as at least 14ĝ€"23% of that of ammonium in the plume. Enhanced sub- and supersaturated water uptake and reduced refractive indices were coincident with lower organic mass fractions, higher nitrate mass fractions, and the detection of amines. The likelihood of suppressed droplet growth owing to kinetic limitations from hydrophobic organic material is explored. After removing effects associated with size distribution and mixing state, the normalized activated fraction of cloud condensation nuclei (CCN) increased as a function of the subsaturated hygroscopic growth factor, with the highest activated fractions being consistent with relatively lower organic mass fractions and higher nitrate mass fractions. Subsaturated hygroscopic growth factors for the organic fraction of the aerosol are estimated based on employing the Zdanovskii-Stokes Robinson (ZSR) mixing rule. Representative values for a parameterization treating particle water uptake in both the sub- and supersaturated regimes are reported for incorporation into atmospheric models.

European Geosciences Union2008

Hygroscopicity and composition of California CCN during summer 2010

Athanasios Nenes

We present an overview and analysis of cloud condensation nuclei (CCN) sampled in California by a NOAA WP-3D aircraft during the 2010 CalNex project. Four distinct geographical regions are characterized, including the Los Angeles basin, the San Joaquin and Sacramento Valleys, and the eastern Pacific Ocean west of southern California. Median size distributions in the Central Valley were unimodal (Dg ∼ 25nm) with a larger fraction of organic species and smaller fraction of nitrate species in the Sacramento Valley aerosol than in the San Joaquin Valley aerosol. Size distributions in the Los Angeles basin and marine outflow were bimodal (geometric mean diameter, Dg ∼ 30, 90-100nm) with similar organic fractions and some replacement of nitrate with sulfate in the marine outflow. Both fine particle and CCN concentrations were found to decrease rapidly above the planetary boundary layer (∼2 km altitude), with CCN concentrations in the boundary layer ranging from ∼102-104cm-3 STP, while fine particle concentrations (0.004-1 m diameters) ranged from ∼103-10 5 cm-3 STP. The CCN-active number fraction varied between 0-100% in the Los Angeles Basin and Marine Outflow, but was substantially lower (0-40%) in the San Joaquin and Sacramento Valleys. Values of the hygroscopicity parameter, , inferred from the CCN measurements varied from 0.1-0.25, with the highest values in the marine outflow and the lowest values in the Sacramento Valley. The values agreed well with the predictions based on size-resolved aerosol composition, but were overpredicted by almost twofold when size-averaged composition was used. CCN closure was assessed for simplified compositional and mixing state assumptions, and it was found that assuming the aerosol to be internally mixed overpredicted CCN concentrations by 30-75% for all air mass types except within the Sacramento Valley, where good closure (overprediction < 10%) was achieved by assuming insoluble organics. Assuming an externally-mixed aerosol fraction or incorporating size-resolved composition data improved closure in the other three regions, consistent with the bimodal nature of the aerosol size distribution. © 2012 by the American Geophysical Union.

Blackwell Publishing Ltd2012

The 2010 California Research at the Nexus of Air Quality and Climate Change (CalNex) field study

Athanasios Nenes

Blackwell Publishing Ltd2013

Comprehensive airborne characterization of aerosol from a major bovine source

Athanasios Nenes

European Geosciences Union2008

Hygroscopicity and composition of California CCN during summer 2010

Athanasios Nenes

Blackwell Publishing Ltd2012