The compiled and quality-assured dataset as well as maps produced as part of the assessment are fully accessible to the wider scientific community for further applications e. Vet et al. Even in regions where sampling is relatively abundant, little information exists for phosphorus, organic forms of nitrogen, organic acids, and other important forms of carbon in atmospheric deposition. Measurements of these species are required to improve our understanding of biogeochemical cycling, the effects of deposition on ecosystem health, and the role of atmospheric deposition on climate change.
Measurement-based estimates of total deposition require not only high quality precipitation concentrations and wet deposition measurements of major ions, but also routine estimates of the corresponding chemicals that are dry deposited.
Direct measurements of dry deposition are not currently operationally feasible, thus, there is a need for a robust method for inferring dry deposition fluxes using concentration measurements of gaseous and aerosol species and model-estimated deposition velocities. Currently, measurement-based inferential estimates of dry deposition are available only for a few countries e. Efforts are presently under consideration to develop laboratory intercomparison methods paralleling existing programs for assessing data quality for wet precipitation measurement laboratories. Emerging technologies, such as satellite measurements and other remote sensing instruments, offer the potential to augment these surface measurements.
Chemical transport models are also critical tools, since in-situ measurements have limited geographic and temporal coverage and will never provide adequate spatial or temporal coverage to estimate total atmospheric deposition on a global scale. The most suitable scientific approach for this activity is the emerging technique of measurement-model fusion for total atmospheric deposition.
The fusion of measurement and model results requires data assimilation and mapping techniques. In order to enhance geographical coverage, GAW works in close cooperation with major regional precipitation and air monitoring networks:. An important key aspect to the success of any measurement programme is the accuracy of sample chemical analysis.
These laboratory inter-comparison studies, initiated in , are designed to assess and track the performance of laboratories based on data quality objectives for major ions typically found in precipitation see GAW Report No. Instead of concentrating on atmospheric chemistry in isolation, the focus is now on seeing it as one part of a single system with the rest of the atmosphere , biosphere , and geosphere. An especially important driver for this is the links between chemistry and climate, such as the effects of changing climate on the recovery of the ozone hole and vice versa but also interaction of the composition of the atmosphere with the oceans and terrestrial ecosystems.
Observations, laboratory measurements, and modeling are the three central elements of atmospheric chemistry. Progress in this field is often driven by interactions between these components and they form an integrated whole. For example, observations may tell us that more of a chemical compound exists than previously thought possible.
This would stimulate new modeling and laboratory studies, which would increase our scientific understanding to a point where the observations can be explained. Observations are essential to our understanding of atmospheric chemistry.
Routine observations of chemical composition provide information about changes in atmospheric composition over time. One important example of this is the Keeling Curve—a series of measurements from to today—that show a steady rise in the concentration of carbon dioxide. These types of observations are conducted in observatories, such as that on Mauna Loa , and on mobile platforms such as aircraft for instance, the UK's Facility for Airborne Atmospheric Measurements , ships, and balloons.
Surface observations provide long-term records at high resolution in terms of time, but they are limited in the vertical and horizontal space they provide observations from. Some surface-based instruments, such as LIDAR, can provide concentration profiles of chemical compounds and aerosols, but they are restricted in the horizontal region they can cover.
Many observations are available online in Atmospheric Chemistry Observational Databases. Measurements made in the laboratory are essential to our understanding of the sources and sinks of pollutants and naturally occurring compounds.
Willis Carrier — made a significant advance in by providing a convenient calibration chart that allowed relativity humidity and absolute water vapor content to be read off by simply locating the intersection of the wet- and dry-bulb temperatures Gatley However, even when models reproduce measured mass concentrations, more specific properties such as volatility and O:C ratio may not be consistent Chen et al. A molecular taxonomy has evolved in which an individual species is characterized by its carbon number n C , oxygen number n O , elemental ratios H:C and O:C , and volatility vapor pressure. It is known that this ability is strongly a function of temperature, and controlled by the physical characteristics and chemical composition of the aerosol particles in a fundamentally different way from CCN. Once organics partition into the particle phase, they can be further transformed chemically into dimers, oligomers, and other higher-molecular-mass compounds Kalberer et al.
Lab studies tell us which gases react with one another and how fast they react. Measurements of interest include reactions in the gas phase, on surfaces, and in water. Of additional significance is photochemistry , which quantifies how quickly molecules are split apart by sunlight and the types of products formed, plus thermodynamic data such as Henry's law coefficients. To synthesize and test the theoretical understanding of atmospheric chemistry, computer models are constructed.
Numerical models solve the differential equations governing the concentrations of chemicals in the atmosphere. They can range from simple to highly complex. One common trade-off in numerical models is between the number of chemical compounds and chemical reactions modeled versus the representation of transport and mixing in the atmosphere.
For example, a box model might include hundreds or even thousands of chemical reactions but will only have a very crude representation of mixing in the atmosphere. By contrast, 3D models represent many of the physical processes of the atmosphere but due to constraints on computer resources will have far fewer chemical reactions and compounds.
Models can be used to interpret observations, test understanding of chemical reactions, and predict future concentrations of chemical compounds in the atmosphere. One important current trend is for atmospheric chemistry modules to become one part of Earth system models in which the links between climate, atmospheric composition, and the biosphere can be studied. Some models are constructed by automatic code generators.
In this approach, a set of constituents are chosen and the automatic code generator then selects the reactions involving those constituents from a set of reaction databases. Once the reactions have been chosen, the ordinary differential equations ODE that describe the changes over time can be automatically constructed. New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation.
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