20% of US electricity from wind will have limited impacts on system efficiency and regional climate.

Impacts from current and future wind turbine (WT) deployments necessary to achieve 20% electricity from wind are analyzed using high resolution numerical simulations over the eastern USA. Theoretical scenarios for future deployments are based on repowering (i.e. replacing with higher capacity WTs) thus avoiding competition for land. Simulations for the contemporary climate and current WT deployments exhibit good agreement with observed electricity generation efficiency (gross capacity factors (CF) from simulations = 45-48%, while net CF for WT installed in 2016 = 42.5%). Under the scenario of quadrupled installed capacity there is a small decrease in system-wide efficiency as indicated by annual mean CF. This difference is approximately equal to that from the two simulation years and may reflect saturation of the wind resource in some areas. WT modify the local near-surface climate in the grid cells where they are deployed. The simulated impact on near-surface climate properties at both the regional and local scales does not increase with increasing WT installed capacity. Climate impacts from WT are modest compared to regional changes induced by historical changes in land cover and to the global temperature perturbation induced by use of coal to generate an equivalent amount of electricity.

Assessing climate change impacts on the near-term stability of the wind energy resource over the United States.

The energy sector comprises approximately two-thirds of global total greenhouse gas emissions. For this and other reasons, renewable energy resources including wind power are being increasingly harnessed to provide electricity generation potential with negligible emissions of carbon dioxide. The wind energy resource is naturally a function of the climate system because the "fuel" is the incident wind speed and thus is determined by the atmospheric circulation. Some recent articles have reported historical declines in measured near-surface wind speeds, leading some to question the continued viability of the wind energy industry. Here we briefly articulate the challenges inherent in accurately quantifying and attributing historical tendencies and making robust projections of likely future wind resources. We then analyze simulations from the current generation of regional climate models and show, at least for the next 50 years, the wind resource in the regions of greatest wind energy penetration will not move beyond the historical envelope of variability. Thus this work suggests that the wind energy industry can, and will, continue to make a contribution to electricity provision in these regions for at least the next several decades.

Modeling the impact of sea-spray on particle concentrations in a coastal city.

With the worlds population becoming increasingly focused on coastal locations there is a need to better understand the interactions between anthropogenic emissions and marine atmospheres. Herein an atmospheric chemistry-transport model is used to assess the impacts of sea-spray chemistry on the particle composition in and downwind of a coastal city--Vancouver, British Columbia. It is shown that the model can reasonably represent the average features of the gas phase and particle climate relative to in situ measurements. It is further demonstrated that reactions in/on sea-spray affect the entire particle ensemble and particularly the size distribution of particle nitrate, but that the importance of these heterogeneous reactions is critically dependent on both the initial vertical profile of sea spray and the sea-spray source functions. The results emphasize the need for improved understanding of sea spray production and dispersion and further that model analyses of air quality in coastal cities conducted without inclusion of sea-spray interactions may yield mis-leading results in terms of emission sensitivities of particle composition and concentrations.

Particle fluxes above forests: observations, methodological considerations and method comparisons.

This paper reports a study designed to test, evaluate and compare micro-meteorological methods for determining the particle number flux above forest canopies. Half-hour average particle number fluxes above a representative broad-leaved forest in Denmark derived using eddy covariance range from -7x10(7) m(-2) s(-1) (1st percentile) to 5x10(7) m(-2) s(-1) (99th percentile), and have a median value of -1.6x10(6) m(-2) s(-1). The statistical uncertainties associated with the particle number flux estimates are larger than those for momentum fluxes and imply that in this data set approximately half of the particle number fluxes are not statistically different to zero. Particle number fluxes from relaxed eddy accumulation (REA) and eddy covariance are highly correlated and of almost identical magnitude. Flux estimates from the co-spectral and dissipation methods are also correlated with those from eddy covariance but exhibit higher absolute magnitude of fluxes.

Nitrogen deposition to and cycling in a deciduous forest.

The project described here seeks to answer questions regarding the role increased nitrogen (N) deposition is playing in enhanced carbon (C) sequestration in temperate mid-latitude forests, using detailed measurements from an AmeriFlux tower in southern Indiana (Morgan-Monroe State Forest, or MMSF). The measurements indicate an average atmosphere-surface N flux of approximately 6 mg-N m(-2) day(-1) during the 2000 growing season, with approximately 40% coming from dry deposition of ammonia (NH3), nitric acid (HNO3), and particle-bound N. Wet deposition and throughfall measurements indicate significant canopy uptake of N (particularly NH4+) at the site, leading to a net canopy exchange (NCE) of -6 kg-N ha(-1) for the growing season. These data are used in combination with data on the aboveground C:N ratio, litterfall flux, and soil net N mineralization rates to indicate the level of potential perturbation of C sequestration at this site.

REVEAL II: seasonality and spatial variability of particle and visibility conditions in the Fraser Valley.

This paper presents data collected during a year-long field experiment (REVEAL II) in the Fraser Valley, British Columbia. The data are used to provide information regarding ambient visibility conditions and fine particle concentrations in the valley. Although average fine mass measured during REVEAL II was 8-9 microg m(-3), the fine particle mass has high light-scattering efficiencies and the visual range is frequently below publicly defined acceptable levels. For example, data indicate that during the fall the visual range is frequently below 20 km even under favorable meteorological conditions. Source apportionment analyses of mass and particle light-scattering indicate motor vehicles may contribute as much as 40% of the fine particle mass in the central valley and up to one-third of the particle light-scattering. In addition to characterizing conditions in the Fraser Valley, slides taken at a number of sites during REVEAL II are used to evaluate a simple method for obtaining (classed) quantitative estimates of visual range from this medium without requiring access to specialized instrumentation.

Secondary organic aerosols: formation potential and ambient data.

Organic aerosols comprise a significant fraction of the total atmospheric particle loading and are associated with radiative forcing and health impacts. Ambient organic aerosol concentrations contain both a primary and secondary component. Herein, fractional aerosol coefficients (FAC) are used in conjunction with measurements of volatile organic compounds (VOC) to predict the formation potential of secondary organic aerosols (SOA) in the Lower Fraser Valley (LFV) of British Columbia. The predicted concentrations of SOA show reasonable accord with ambient aerosol measurements and indicate considerable seasonal variability in SOA potential. Particulate carbon contributes only approx. 3% of total carbon concentrations in the LFV, and it is shown that variability in total carbon concentrations is significantly larger than variability in gas/particle partitioning.

PM10 in Canada.

Annual mean PM10 concentrations in Canadian cities are between five and eight times estimated background levels. Federal and Provincial agencies in Canada are currently reviewing particulate standards, and considering replacing current total suspended particulate (TSP) standards with standards to regulate PM10 (thoracic particles) because epidemiological research suggests that this size fraction is active in the production of adverse health impacts. This paper documents the spatial and temporal variability of current particulate levels in Canada, and compares them with TSP standards presently implemented in Canada and PM10 standards as applied by the US EPA, state of California and the World Health Organization (WHO). Twenty-four-hour averaged PM10 data from the 52 sites described here exceed the standard as applied in California on up to 35% of monitoring days. The threshold suggested by the WHO for 24-h averaged concentrations is passed at the majority of the sites on approximately 5% of monitoring days.