Atmospheric fine particulate matter

Except for fine particulate matter (0.2 /xm or less), which may remain airborne for long periods of time, and gases such as carbon monoxide, which do not react readily, most airborne pollutants are eventually removed from the atmosphere by sedimentation, reaction, or dry or wet deposition. 

Airborne particulate matter, which includes dust, dirt, soot, smoke, and liquid droplets emitted into the air, is small enough to be suspended in the atmosphere. Airborne particulate matter may be a complex mixture of organic and inorganic substances. They can be characterized by their physical attributes, which influence their transport and deposition, and their chemical composition, which influences their effect on health. The physical attributes of airborne particulates include mass concentration and size distribution. Ambient levels of mass concentration are measured in micrograms per cubic meter (mg/m ) size attributes are usually measured in aerodynamic diameter. Particulate matter (PM) exceeding 2.5 microns (/i) in aerodynamic diameter is generally defined as coarse particles, while particles smaller than 2.5 mm (PMj,) are called fine particles. 

Jutze, G. A., and K. E. Foster (TR-2 Air Pollution Measurements Committee). Recommended standard method for atmospheric sampling of fine particulate matter by filter media—high-volume sampler. J. Air Pollut. Control Assoc. 17 17-25, 1%7. 

Recent research has shown that combustion sources can generate radicals that are stabilized by associated with particulate matter. This same particulate matter becomes a component of airborne PM2.5. (fine particulate matter (smaller than 2.5 microns in diameter). PM2.5 is known to initiate lung cancer and cardiopulmonary disease however, the mechanism has not been identified. DNA and cellular assay results indicate that combustion and PM2.5 can cause radical induced damage to DNA. Based on electron paramagnetic resonance (EPR) studies, the responsible species appear to be semiquinone-type radicals. These studies reveal that radicals, heretofore thought to be too unstable to survive in the atmosphere, can be stabilized by association with particles and initiate biological damage. 

Understanding heterogeneous chemistry (4) the structure of natural organic matter (2) air sources and characterization of toxics (1) speciation of toxic metals (1) smokestack emissions beyond SOx and NOx (1) chemical sources of toxicity of fine particulate matter (PM2.5) (1) environmentally persistent free radicals (1) understanding of greenhouse gases in the atmosphere (carbon cycles and sinks)... 

The impact of the emission cuts is beginning to be noticed, although more with respect to deposition than ecosystem recovery. The U.S. Environmental Protection Agency soon reported declines in wet sulphate deposition in the order of 10 to 25% across the eastern United States. There are also possible improvements with respect to dry deposition of sulphates, fine particulate matter concentrations, and visibility. Aquatic and terrestrial ecosystems respond slowly, and it is not surprising that evidence of ecosystem improvements would trail behind trends in reduced atmospheric transport and deposition. The EPA, while modest in its assessment of the environmental benefits to be accrued from reduced acidification, has been rather bullish about the investment in human health benefits represented by acid rain controls. It expects SO emission cuts to reduce American health costs by 10 billion annually, through reduced morbidity and mortality, and these savings are projected to rise to 40 billion annually by 2010 (EPA 1995). 

Finally, particulate matter (PM), or the solid and liquid particles that are released into the atmosphere, comes from both the actual emissions of particulates and the reaction between atmospheric molecules and SO2 or NO. Particulate matter can be divided based on the size of the particle. Health effects include respiratory distress as well as cancer and permanent lung damage. Fine particulate matter (<2.5 microns in size, PM 2.5) is a major cause of reduced visibility, or haze, in many parts of the country. The EPA notes visibility in several of our nation s national parks and wilderness areas has been negatively affected by high particulate levels in the air. Particulate emissions that are not the result of other pollutants or natural causes come primarily from the industrial sector (EPA 1995). 

Pollutants particularly suited to transport over long distances within the atmosphere are those that are removed only ineffectively by chemical reactions or wet and dry deposition processes. Examples include fine particulate matter (PM2 5) and ozone. In the case of fine particles, the deposition processes are inefficient and the particles may remain airborne for many days. In the case of ozone, dry deposition is relatively efficient but operates mainly dtrring daytime, when photochemistry rapidly replaces depleted ozone. At nighttime, dry deposition occurs from within a shallow, stable layer of air in contact with the grotmd, while above that layer the ozone remains imaffectedby dry deposition and is depleted by only rather slow chemical reaction processes. Once stmshine mixes the atmosphere... 

In addition to gases dissolving in another gas, as is the case with the atmosphere, sohds and hquids can also dissolve in gases. An example of solids that dissolve in gases is again the atmosphere, which frequently has dust, soot, or other fine particulate matter suspended in it. Winds serve to maintain the suspension, but in absolutely still air, sohd materials settle out... 

When a liquid or solid substance is emitted to the air as particulate matter, its properties and effects may be changed. As a substance is broken up into smaller and smaller particles, more of its surface area is exposed to the air. Under these circumstances, the substance, whatever its chemical composition, tends to combine physically or chemically with other particles or gases in the atmosphere. The resulting combinations are frequently unpredictable. Very small aerosol particles (from 0.001 to 0.1 Im) can act as condensation nuclei to facilitate the condensation of water vapor, thus promoting the formation of fog and ground mist. Particles less than 2 or 3 [Lm in size (about half by weight of the particles suspended in urban air) can penetrate the mucous membrane and attract and convey harmful chemicals such as sulfur dioxide. In order to address the special concerns related to the effects of very fine, iuhalable particulates, EPA replaced its ambient air standards for total suspended particulates (TSP) with standards for particlute matter less than 10 [Lm in size (PM, ). 

ITie major component of atmospheric haze is sulfate particulate matter (particularly ammonium sulfate), along with varying amounts of nitrate particulate matter, which in some areas can equal the sulfate. Other components include graphitic material, fine fly ash, and organic aerosols. 

The sources of particulate matter in the atmosphere can be primary, directly injected into the atmosphere, or secondary, formed in the atmosphere by gas-to-particle conversion processes (13). The primary sources of fine particles are combustion processes, e.g., power plants and diesel... 

Health effects attributed to sulfur oxides are likely due to exposure to sulfur dioxide, sulfate aerosols, and sulfur dioxide adsorbed onto particulate matter. Alone, sulfur dioxide will dissolve in the watery fluids of the upper respiratory system and be absorbed into the bloodstream. Sulfur dioxide reacts with other substances in the atmosphere to form sulfate aerosols. Since most sulfate aerosols are part of PMj 5, they may have an important role in the health impacts associated with fine particulates. However, sulfate aerosols can be transported long distances through the atmosphere before deposition actually occurs. Average sulfate aerosol concentrations are about 40% of average fine particulate levels in regions where fuels with high sulfur content are commonly used. Sulfur dioxide adsorbed on particles can be carried deep into the pulmonary system. Therefore, reducing concentrations of particulate matter may also reduce the health impacts of sulfur dioxide. Acid aerosols affect respiratory and sensory functions. 

In alkaline soils, the major components of the soil solution are Ni2+ and Ni(OH)+ in acidic soils the main solution species are Ni2+, NiS04, and NiHP04 (USPHS 1993). Atmospheric nickel exists mostly in the form of fine respirable particles less than 2 pm in diameter (NRCC 1981), usually suspended onto particulate matter (USEPA 1986). 

Organic compounds, natural, fossil or anthropogenic, can be used to provide a chemical mass balance for atmospheric particles and a receptor model was developed that relates source contributions to mass concentrations in airborne fine particles. The approach uses organic compound distributions in both source and ambient samples to determine source contributions to the airborne particulate matter. This method was validated for southern California and is being applied in numerous other airsheds. ... 

The results presented here suggest a new mechanism of toxicity for PM 5 based on sustained hydroxyl radical generation by the semiquinone radicals present in PM 5. Because a substantial fraction of the fine particles in the atmosphere arises from combustion sources (9), it is possible that the deleterious health effects associated with PM2 5 can be at least partially ascribed to radicals associated with combustion-generated particulate matter. 

Wildfires represent a major source of atmospheric particulate matter (PM) especially fine particles with diameter <2.5 pm (PM2.5). High ambient fine particle concentrations are associated with serious health problems [4], At times extensive... 

Farinha, M.M., Slejkovec, Z., van Elteren, J.T. et al. (2004) Arsenic speciation in lichens and in coarse and fine airborne particulate matter by HPLC-UV-HG-AFS. Journal of Atmospheric Chemistry, 49(1-3), 343-53. 

Eatough, D.J., A. Wadsworth, D.A. Eatough, J.W. Crawford, L.D. Hansen, and E.A. Lewis, 1993. A multi-system, multi-channel diffusion denuder sampler for the determination of fine particulate organic matter in the atmosphere. Atmos. Environ. 27 1213-1219. 

No data were located on the residence time of radium in the atmosphere or its deposition rate. However, data for other elements adsorbed to particulate matter indicate that the residence time for fine particles is about 1 to 10 days (EPA 1982b Keitz 1980). Radium may, therefore, be subject to long-range transport in the atmosphere. 

Most of the studies on size-resolved aerosol mass concentrations in areas with different levels of pollution show that particulate matter typically exhibit a bimodal distribution, with most of their mass being found in the submicron size range (dae < 1pm) and an additional minor mode in the coarse fraction (1 < dae < 10 pm) (Maenhaut et al., 2002 Smolfk et al., 2003 Wang et al., 2003 Gajananda et al., 2005 Samara and Voutsa, 2005). However, with instrumentation allowing more precise measurements, the aerosol mass size distribution was found to be multimodal with the preponderance of a fine mode (dae < 0.2 pm) and an accumulation mode (dae 0.5pm), with a minor coarse mode at d 3-4pm (Raes et al., 2000 Pillai and Moorthy, 2001 Berner et al., 2004). Traditionally, atmospheric researchers classify airborne particles into three size classes coarse (2.5 < c/ ie < 10pm), fine... 

Ames, M., Gullu, G. and Olmez, I. (1998) Atmospheric mercury in the vapor phase, and in fine and coarse particulate matter at Perch River, New York. Atmos. Environ., 32,865-872. 

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