Emissions ambient concentrations

Emissions of CO in the United States peaked in the late 1960s, but have decreased consistendy since that time as transportation sector emissions significandy decreased. Between 1968 and 1983, CO emissions from new passenger cars were reduced by 96% (see Exhaust CONTUOL, automotive). This has been partially offset by an increase in the number of vehicle-miles traveled annually. Even so, there has been a steady decline in the CO concentrations across the United States and the decline is expected to continue until the late 1990s without the implementation of any additional emissions-reduction measures. In 1989, there were still 41 U.S. urban areas that exceeded the CO NAAQS on one or mote days per year, but the number of exceedances declined by about 80% from 1980 to 1989. Over the same time period, nationwide CO emissions decreased 23%, and ambient concentrations declined by 25% (4). 

Emissions of gases or particles less than 20 microns (larger particles settle more quickly due to gravitational effects) disperse with an origin and plume centerline at the effective stack height. Pollutant concentrations are greatest within one standard deviation of the plume centerline. Thus, the determination of the value of these standard deviations is an important factor in calculating ambient concentrations. 

Between 1976 and 1995, ambient concentrations of lead in the United States declined by 97%. Between 1994 and 1995, national average lead concentrations remained unchanged at 0.04 pg/m3 even though lead emissions declined 1% (EPA 1996h). 

Priority la Ambient concentrations significantly above primary standards and due to emission from point sources. 

The commonly used units of expression are explained in Table, 6-2. Expressing concentration data in micrograms per cubic meter facilitates relating ambient concentrations to emission. This practice is generally accepted as standard by the Environmental Protection Agency (epa) in the United States and similar agencies in other countries. 

Caceres T, Soto H, Lissi E, et al. 1983. Indoor house pollution Appliance emissions and indoor ambient concentrations. Atmos Environ 17(5) 1009-1013. 

Receptor models are used to determine the source contributions to ambient particulate matter loadings at a sampling site based on common properties between source and receptor. This is in contrast to a source model which starts with emission rates and meteorological measurements to predict an ambient concentration. 

Source-oriented atmospheric dispersion modeling has been the major tool used in attributing ambient concentrations to source emissions. With the development of inexpensive and rapid chemical analysis techniques for dividing ambient and source particulate matter into its components has come another approach, the receptor model. 

While the source-oriented model begins with measurements at the source (i.e., emission rates for the period under study), and estimates ambient concentrations, the receptor-oriented model begins with the actual ambient measurements and estimates the source contributions to them. The receptor model relies on properties of the aerosol which are common to source and receptor and that are unique to specific source types. These properties are composition, size and variability. 

The constants k relate the source emissions to the ambient concentrations according to the relationship... 

The use of dispersion-normalized data is equivalent to adjusting all ambient concentrations to the same dispersion conditions and assuming that the remaining variations in concentrations are due to variations in source emissions. Although this is a logical approach conceptually, it is not known at present what uncertainties are associated with the use of a dispersion factor calculated from a 7 A.M. determination of mixing height and wind-speed. 

As discussed in Chapter 1, much of our understanding of the chemistry of our atmosphere is based on early studies of air pollution these are often treated in the context of an overall system. This approach starts with the various sources of anthropogenic and natural emissions and tracks the resulting pollutants through their atmospheric transport, transformations, and ambient concentrations—on local, regional, and global scales—to their ultimate chemical and physical fates, including their impacts on our health and environment. 

Grosjean, D., Organic Acids in Southern California Air Ambient Concentrations, Mobile Source Emissions, in Situ Formation, and Removal Processes, Environ. ScL Technol., 23, 1506-1514(1989). 

FIGURE 10.22 Direct mutagenicity of ambient particles (mutagen density, rev m-3, TA98, —S9) as a function of ambient concentrations of 2-nitropyrene, a directly mutagenic product of a gas-phase atmospheric reaction initiated by OH radical attack on pyrene. Samples collected at six sites in California with different types of emissions ( ) Glendora (O) Yuba City ( ) Concord ( ) Mammoth Lakes ( a ) Oildale ( ) Reseda (see Fig. 10.22) (adapted from Atkinson et al., 1988a). 

Grosjean, E., D. Grosjean, and R. A. Rasmussen, Ambient Concentrations, Sources, Emission Rates, and Photochemical Reactivity of C2-C1(l Hydrocarbons in Porto Alegre, Brazil, Environ. Sci. Technol., 32, 2061-2069 (1998b). 

Finally the so-called mono- and macro-tracer approaches can be applied for determining source contributions. These methods rely on the fact that a number of chemical compounds can be directly linked to biomass combustion emissions. For example, ambient concentrations of water-soluble potassium, certain PAHs, anhydrosugars and many other tracers have been used as indicators for the impact of biomass burning. When the fractions of one of these tracers in PM and carbonaceous aerosols emitted by wood burning are known (emissions ratios), the contribution of wood burning at a receptor site can be calculated based on the concentration of the considered tracer (mono tracer method). 

There is currently no air quality regulation in Europe or any other part of the world to control the ambient concentrations of particles on a number basis. However, particle numbers are currently being regulated at vehicle tailpipe exhausts through Euro-5 and Euro-6 emission standards [103]. These are the first ever limits of this kind, though only applicable in Europe, to control the emissions of particle numbers at source. These standards include a lower size limit of 23 nm for minimising the... 

Current research on the atmospheric cycling of sulfur compounds involves the experimental determination of reaction rates and pathways (see Plane review, this volume) and the field measurement of ambient concentrations of oceanic emissions and their oxidation products. Photochemical models of tropospheric chemistry can predict the lifetime of DMS and H2S in marine air however there is considerable uncertainty in both the concentrations and perhaps in the identity of the oxidants involved. The ability of such models to simulate observed variations in ambient concentrations of sulfur gases is thus a valuable test of our assumptions regarding the rates and mechanisms of sulfur cycling through the marine atmosphere. 

Using a one-dimensional Monte Carlo analysis to estimate population exposure and dose uncertainty distributions for particulate matter, where model inputs and parameters (e.g. ambient concentrations, indoor particulate matter emission rates from environmental tobacco smoke, indoor air exchange rates, building penetration values, particle deposition rates) are represented probabilistically with distributions statistically fitted to all available relevant data. 

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