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Learn more Check out. Related Information. Close Figure Viewer. Browse All Figures Return to Figure. This manuscript concludes that carbon dioxide emissions from fossil-fuel combustion continue to increase with time and that while much is known about the overall characteristics of these emissions, much is still to be learned about the detailed characteristics of these emissions.
Each analyzer has three sample inlets for profile sampling, and a complete vertical profile is obtained every 15 min. The long-term stability of the systems in the field is typically better than 0.
The instrumentation is fully automated and includes sensors for measuring a variety of status parameters, such as temperatures, pressures, and flow rates, that are inputs for automated alerts and quality control algorithms. Detailed and time-dependent uncertainty estimates have been constructed for all of the gases, and the uncertainty framework could be readily adapted to other species or analysis systems.
The design emphasizes use of off-the-shelf parts and modularity to facilitate network operations and ease of maintenance. Recurrent problems and limitations of the current system are discussed along with general recommendations for high-accuracy trace-gas monitoring. The network is a key component of the North American Carbon Program and a useful model for future research-grade operational greenhouse gas monitoring efforts. Empirical age spectra for the lower tropical stratosphere from the tropopause to similar to Our method provides accurate and unambiguous mean ages for this region which are difficult to obtain by simple analysis of lag times from tracer measurements.
For example, at K the mean age relative to the tropical tropopause was 0. Profiles of stratospheric water vapor, generated from the derived age spectra with a stratospheric boundary condition based on observed tropical tropopause temperatures, are consistent with in situ observations of H2O. Comparison of the predicted water vapor seasonal cycle with satellite observations suggests that satellite-borne instruments underestimate the amplitude near the tropical tropopause. We relate the empirical age spectra to the analytic solution for the 1-D advection-diffusion tracer continuity equation to obtain seasonally resolved estimates of the ascent rate and the vertical diffusion coefficient.
The derived age spectra provide a unique observation-based diagnostic for evaluating the simulation of tracer transport in models. Empirical age spectra for the northern midlatitude lower stratosphere were derived using a genetic algorithm constrained by in situ observations of CO2 and N2O. An age spectrum is the probability distribution function describing the ensemble of transit times between the tropical tropopause and a point in the stratosphere. Age spectra with two distinct maxima fit observed CO2 mixing ratios significantly better than age spectra consisting of a single peak.
The mean transit time mean age of the younger peak increased with altitude from the tropopause to similar to1 year at We argue that the younger peak represents rapid quasihorizontal transport of air from the tropics, while the older peak represents downwelling of air from higher altitudes in the mean meridional circulation. Mean ages for the younger and older peaks provide estimates of the residence times fur air in the lower and middle stratosphere, respectively. The clear separation of the peaks implies a significant altitude region where there is little meridional exchange between midlatitudes and the tropics.
High altitude mountaintop observatories provide the opportunity to study aerosol properties in the free troposphere without the added expense and difficulty of making airborne measurements. The amount of light absorption and scattering observed at these high altitude sites either peaks in the spring or it has a broad spring to summer enhancement.
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The seasonal variation of in-situ aerosol light extinction from these high altitude measurements is in excellent agreement with extinction values derived from CALIPSO lidar measurements. Analysis of the systematic variability among in-situ aerosol properties shows that these relationships can be used to infer aerosol types.
Variability inmonthly cycles of RFE corresponds with changes in single scattering albedo and hemispheric backscatter fraction. The greatest discrepancy occurs formonths with lowaerosol loadingwhere the observed variability of single scattering albedo and backscatter fraction is the greatest. A small airplane made aerosol optical property light absorption and light scattering vertical profile measurements over a rural Oklahoma site between March and December The aerosol profiles obtained during these 8 yr of measurements suggest significant seasonal differences in aerosol loading scattering and absorption.
The highest amounts of scattering and absorbing aerosol are observed during the summer and the lowest loading occurs during the winter. The relative contribution of aerosol absorption is highest in the winter i. Aerosol absorption generally decreased with altitude below 1. Aerosol scattering decreased sharply with altitude below 1. The observed seasonal cycle of aerosol loading corresponds with changes in air mass back trajectories: the aerosol scattering was higher when transport was from polluted areas e.
We have used Level 1. This systematic difference in the comparisons suggests a bias in one or both of the methods, but we cannot assess whether the AERONET retrievals are biased towards high absorption or the in situ measurements are biased low. Many of the sites are located in regions influenced by specific aerosol types Asian and Saharan desert dust, Asian pollution, biomass burning, etc.
The result is a long-term cooperative program making atmospheric measurements that are directly comparable with those from all the other network stations and with shared data access. Transport of pollutants emitted in one region to another region may add to the impact of local emissions. In this work, Lagrangian particle dispersion model simulations show the amounts of tracers that are transported within and among four regions, Southern California, the San Francisco Bay Area, the Central Valley, and the rest of the state.
Tracers of automobile emissions and one type of agricultural emission are used. Tracer mixing ratios are compared to airborne and ground-based measurements.
The age of tracers in each location is also presented. Vertical profiles and diurnal cycles help to clarify the transport process. As is well known, Southern California emissions are transported to the east and affect the desert areas, and Bay Area automobile emissions are an important source of pollutants in the San Joaquin Valley. A novel result is that the Southern California Bight is filled with a mixture of well-aged carbon monoxide tracer from Southern California and the Bay Area. Air over the Bight is also affected by the agricultural emissions represented by the agricultural tracer, dominantly from the Central Valley where its sources are largest.
There is no indication of transport from Southern California to the Central Valley. Emissions from the Central Valley do make their way to Southern California, as shown by the agricultural tracer, but automobile emissions from the Valley are insignificant in Southern California. Two extreme cases of aerosol optics from the Reno Aerosol Optics Experiment are used to develop a model-based calibration scheme for the 7-wavelength aethalometer. The cases include those of very white and very dark aerosol samples. The former allows for an assessment of the scattering offset associated with this filter-based method, with the wavelength-dependent scattering measured from a 3-wavelength nephelometer, and interpolated and extrapolated to the 7 wavelengths of the aethalometer.
Black soiling of an architectural limestone during two-year term exposure to urban air in the city of Granada S Spain. Mosunov, and N. Tantalates are also characterized by a high absorption cross-section. Age spectra with two distinct maxima fit observed CO2 mixing ratios significantly better than age spectra consisting of a single peak. ESEM microscopic photographs of moss forming green carpets on the stone surfaces of Palenque heritage. For the example of the sibling telescope in Hobart, several types of sessions will be discussed: an improved tag-along mode for the m antenna Ho , a proper implementation of the twin-mode using the antenna with the shorter slewing time, and an astrometric support mode enabling the observation of weak sources with the AuScope array.
A photoacoustic instrument operating at nm is used to evaluate the filter loading effect caused by aerosol light absorption. Multiple scattering theory is used to analytically obtain a filter-loading correction function. This theory shows that the exponential behavior of light absorption in the strong multiple scattering limit scales as the square root of the total absorption optical depth rather than linearly with optical depth as is commonly assumed with Beer's law. The multiple scattering model also provides a theoretical justification for subtracting a small fraction of aerosol light scattering away from measured apparent light absorption by the filter method.
The model is tested against ambient measurements and is found to require coefficients that are situation specific. Several hypotheses are given for this specificity, and suggested methods for reducing it are discussed. Specific findings are as follows. Simultaneous aerosol light-scattering measurements are required for accurate interpretation of aethalometer data for high aerosol single-scattering albedo.
The aethalometer overpredicts black carbon BC concentration on a fresh filter and underpredicts BC on a loaded filter.
BC and photoacoustic light absorption can be tightly correlated if the data are averaged over the full range of filter loadings and the aerosol source is constant. Theory predicts that the Aethalometer response may be sensitive to filter face velocity, and hence flow rate, to the extent that particle penetration depth depends on face velocity.
Limited understanding of carbon dioxide sinks and sources on land is often linked to the inability to distinguish between the carbon dioxide taken up by photosynthesis, and that released by respiration1, 2. Carbonyl sulphide, a sulphur-containing analogue of carbon dioxide, is also taken up by plants, and could potentially serve as a powerful proxy for photosynthetic carbon dioxide uptake, which cannot be directly measured above the leaf scale.
Indeed, variations in atmospheric concentrations of carbonyl sulphide are closely related to those of carbon dioxide at regional, local and leaf scales3, 4, 5, 6, 7, 8, 9. Here, we use eddy covariance and laser spectroscopy10 to estimate the net exchange of carbon dioxide and carbonyl sulphide across three pine forests, a cotton field and a wheat field in Israel. We estimate gross primary productivity—a measure of ecosystem photosynthesis—directly from the carbonyl sulphide fluxes, and indirectly from carbon dioxide fluxes.
The ratio of carbonyl sulphide to carbon dioxide flux at the ecosystem scale was consistent with the variability in mixing ratios observed on seasonal timescales in the background atmosphere. We suggest that atmospheric measurements of carbonyl sulphide flux could provide an independent constraint on estimates of gross primary productivity, key to projecting the response of the land biosphere to climate change. The majority of the sites showed clear decreasing trends both in the full-length time series, and in the intra-site comparison period of —, especially during the winter months.
This work provides a useful comparison analysis for modelling studies of trends in aerosol number concentrations. Four research groups from the United States US and Europe have provided modeled ozone vertical profiles to conduct this analysis.