Urban polluted aerosol

In previous studies we found that improved emission-control devices (such as hot-side electrostatic precipitaters and wet-scrubber systems) now being installed on modern pulverized-coal-fired power plants modify the quantity, chemical composition, and distribution characteristics of fine aerosol emissions (12,13). Such modifications must be understood to adequately assess human health and environmental hazards, and to apportion the contributions of sources to urban pollutant inventories. 

Another important air-quality parameter, visibility, is closely related to the aerosol extinction coefficient. The extinction coefficient, like the total mass, is an integral function of the particle size distribution. However, for urban pollution it tends to weight the contribution of material in the 0,1 - to I. O-pm size range most heavily (Chapter 5). There is a separate mass based U.S. EPA standard for non-health related effects such as visibility. 

Desert aerosol 3600 m Elevation Marine air masses Marine air masses advected by strong winds from the Atlantic Ocean Urban pollution, inversion layer... 

In the last several years a great deal has been learned about air pollution aerosols (68-71). Although our knowledge is still far from complete, there is general agreement on the nature of urban aerosol size distributions and their interpretation (TO) ... 

It has been established that the principal growth mechanism for urban atmospheric aerosols in the 0.1-1.0 ym diameter size range (the so-called Accxamulation Mode) is gas-to-particle conversion (68,71) The major secondary components in atmospheric aerosols have been identified as sulfates, nitrates and particulate organic species (68,71,72,73). The qualitative picture of polluted... 

Henry, R.C. "A Factor Model of Urban Aerosol Pollution." Ph.D. Dissertation, Oregon Graduate Center, Beaverton, OR 1977. 

Ambient aerosols, particularly those with diameters less than 3pm, are a serious pollution problem. Carbonaceous material is a major component of the fine particle concentration (10 and has undergone extensive study in the past few years (, ) in large part because of the concern that these particles play an Important role in urban haze and community health. 

Particulate carbon in the atmosphere exists predominantly in three forms elemental carbon (soot) with attached hydrocarbons organic compounds and carbonates. Carbonaceous urban fine particles are composed mainly of elemental and organic carbon. These particles can be emitted into the air directly in the particulate state or condense rapidly after Introduction into the atmosphere from an emission source (primary aerosol). Alternatively, they can be formed in the atmosphere by chemical reactions involving gaseous pollutant precursors (secondary aerosol). The rates of formation of secondary carbonaceous aerosol and the details of the formation mechanisms are not well understood. However, an even more fundamental controversy exists regarding... 

This was calculated in the same manner as that described by Cass, Boone and Macias (9). The carbon to lead ratio determined from this inventory can be examined for several limiting cases ranging from the output of an automobile using leaded fuel (C/Pb /2) to aerosol in the well mixed LA air basin with significant secondary conversion of carbon (C/Pb>7). This approach assumes, of course, that lead is present only as a primary pollutant. For highway traffic composed of vehicles and fuel types in the same proportions as for the entire urban area, the ratio of aerosol carbon to lead was calculated to be about 4. 

In short, the same types of aerosol organic products have been identified both in model systems and in polluted urban ambient air and can generally be rationalized based on the oxidation of known constituents of air. The measured yields of organics in the particles can depend on the amount of particle phase available for uptake of the organic if it is semivolatile and partitions between the gas and condensed phases. This partitioning, and its dependence on the amount of condensed phase available, may be at least in part responsible for discrepancies in the yields of secondary organic aerosol reported in a number of studies. 

Swietlicki, E., S. Prui, H.-C. Hansson, and H. Edner, Urban Air Pollution Source Apportionment Using a Combination of Aerosol and Gas Monitoring Techniques," Atmos. Environ., 30, 2795-2809 (1996). 

Morawaska, L., S. Thomas, N. Bofinger, D. Wainwright, and D. Neale, Comprehensive Characterization of Aerosols in a Subtropical Urban Atmosphere Particle Size Distribution and Correlation with Gaseous Pollutants, Atmos. Enriron., 32, 2467-2478 (1998). 

Since 1992 the two Italian stations of Rome, urban site (latitude 41.9° N, longitude 12.5° E, altitude 60 m), and Ispra, semi-rural site (latitude 45.8° N, longitude 8.6° E, altitude 240 m), collect regular continuous measurements of spectral UV (290-325 nm) irradiance by means of Brewer Spectrophotometry. The measured data are compared with the output of the STAR model (System for Transfer of Atmospheric Radiation) [1], STAR is a multiple scattering radiative transfer model which considers all atmospheric factors modulating UV radiation at ground (ozone, aerosol, clouds, pollutants, albedo, pressure, temperature, humidity) [2], The model involves combination of a radiative transfer code, an initialisation procedure and an integration scheme. 

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