collection processes may include monitoring ambient air for the presence of pollutants, directly monitoring emissions sources, or collecting other quantitative information from which air quality information may be deduced. For example, local agencies may employ a particulate matter sampler to determine ambient air quality in a locality over time. Fossil power plants may required to monitor emissions at a flue-gas stack to determine quantities of relevant pollutants emitted. Automobile manufacturers may be required to collect data regarding car sales, which, when combined with technical specifications regarding fuel consumption and efficiency, may be used to estimate total vehicle emissions. In each case, data collection may be short- or long-term, and at varying frequency (e.g., hourly, daily). Air quality laws may include detailed requirements for recording, storing, and submitting relevant information, generally with the ultimate goal of standardizing data practices in order to facilitate data access and manipulation at a later time. Precise requirements may be very difficult to determine without technical training and may change over time in response to, for example, changes in law, changes in policy, changes in available technology, and changes in industry practice. Such requirements may be developed at a national level and reflect consensus or compromise between government agencies, regulated industry, and public interest groups. Once air quality data are collected and submitted, some air quality laws may require government agencies or private parties to provide the public with access to the information - whether the raw data alone, or via tools to make the data more useful, accessible, and understandable. Where public access mandates are general, it may be left to the collecting agency to decide whether and to what extent the data is to be centralized and organized. For example, the United States Environmental Protection Agency, National Oceanic and Atmospheric Administration, National Park Service, and tribal, state, and local agencies coordinate to produce an online mapping and data access tool called AirNow, which provides real-time public access to U.S. air quality index information, searchable by location. Once data are collected and published, they may be used as inputs in mathematical models and forecasts. For example, atmospheric dispersion modeling may be employed to examine the potential impact of new regulatory requirements on existing populations or geographic areas. Such models in turn could drive changes in data collection and reporting requirements. Controversy Proponents of air quality law argue that they have caused or contributed to major