Secondary aerosol particles

Temperature-programmed thermal desorption particle beam MS of collected secondary aerosol particles shows that the major ozonization products of normal alkenes in an environmental chamber include organic hydroperoxides, peroxides, final ozonides and monocarboxylic acids. Attempts to analyze these compounds by GC result in their decomposition to simpler molecules". 

Schuetzle, D., D. Cronn, A. L. Crittenden, and R. J. Charlson (1975). Molecular composition of secondary aerosols and its possible origin. Environ. Sci. TechnoL 9, 838-845. Schuetzle, D., and R. A. Rasmussen (1978). The molecular composition of secondary aerosol particles formed from terpenes. J. Air Pollut. Control Assoc. 28, 236-240. 

Soil-derived partieles sueh as aluminosilicates, CaCOs, and Si02 are the seeond most abundant partiele type in indoor environment of subway stations. The relative abundanee of the sod-derived particles in subway stations are the lowest in the tunnel and the highest at the waiting room. Also secondary particles sueh as nitrates and sulfates are more abundantly encountered in the waiting room than in the platform area. The soil-derived and secondary aerosol particles are likely from the outdoor atmosphere. Therefore, the contents of those particles are higher for the samples eoUeeted at the loeations closer to the outdoor. 

Sources of atmospheric aerosol particles are bulk-to-particle conversion, gas-to-particle conversion, and combustion processes. Bulk-to-particle conversion includes the formation of sea salt, dust, and biogenie partieles. Gas-to-particle formation involves either new particle formation from aerosol precursor gases, or growth of preexisting particles by mass transfer processes between the gas and the partiele phase. Particles derived from gas-to-partiele eonversion processes are also called secondary aerosol particles. Other partieles, sueh as from bulk-to-partiele eonversion processes or combustion particles (soot, fly ash), are called primary aerosol particles. 

Chemical radicals—such as hydroxyl, peroxyhydroxyl, and various alkyl and aryl species—have either been observed in laboratory studies or have been postulated as photochemical reaction intermediates. Atmospheric photochemical reactions also result in the formation of finely divided suspended particles (secondary aerosols), which create atmospheric haze. Their chemical content is enriched with sulfates (from sulfur dioxide), nitrates (from nitrogen dioxide, nitric oxide, and peroxyacylnitrates), ammonium (from ammonia), chloride (from sea salt), water, and oxygenated, sulfiirated, and nitrated organic compounds (from chemical combination of ozone and oxygen with hydrocarbon, sulfur oxide, and nitrogen oxide fragments). ... 

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... 

Because of the gaseous nature of many of the important primary and secondary pollutants, the emphasis in kinetic studies of atmospheric reactions historically has been on gas-phase systems. However, it is now clear that reactions that occur in the liquid phase and on the surfaces of solids and liquids play important roles in such problems as stratospheric ozone depletion (Chapters 12 and 13), acid rain, and fogs (Chapters 7 and 8) and in the growth and properties of aerosol particles (Chapter 9). We therefore briefly discuss reaction kinetics in solution in this section and heterogeneous kinetics in Section E. 

Heterogeneous condensation is secondary aerosol formation by the scavenging of the low-vapor-pressure products onto preexisting particles. If the concentration of particles is sufficiently high, this dominates over the formation of new nuclei via homogeneous nucleation (e.g., Friedlander, 1978, 1980). 

Ziemann, P. J., and P. H. McMurry, Spatial Distribution of Chemical Components in Aerosol Particles As Determined from Secondary Electron Yield Measurements Implications for Mechanisms of Multicomponent Aerosol Crystallization, . /. Colloid Interface Sci., 193, 250-258 (1997). 

The limits to the areal density of deposit for filters are set by clogging of the filter that sets in at typically 100 xg/cm2. The limit of areal density for impactors is set by the problem of particle bounce. This is a serious problem for coarse, dry aerosols but less so for fine, wet, secondary aerosols. Nevertheless, sticky substrates are universally used (19), and deposits are generally limited to a few monolayers of particles for a 2.5- xm particle. This limit amounts to no more than 7 xm of deposit, or, for 1.5- xg/m3 aerosols (per stage), about 1000 xg/cm2 of deposit. 

A further complication is the basic assumption of the statistical methods that source profiles neither change during air transport nor with time. Therefore they cannot be applied strictly to secondary aerosol constituents formed in the atmosphere by gas-to-particle conversion processes. Still, the secondary aerosol constituents tend to be grouped into one source group since they have a common source , i.e. formation in air triggered by solar irradiation. 

Particles in the atmosphere arise from natural sources, such as windbome dust, sea spray and volcanoes, and from anthropogenic activities, such as combustion of fuels. Emitted directly as particles (primary aerosol) or formed in the atmosphere by gas-to-particle conversion processes (secondary aerosol), atmospheric aerosols are generally considered to be the particles that range in from a few nanometres to tens of micrometres in diameter [1]. 

Carbonaceous aerosols in the atmosphere are complex in nature and are found in both coarse particles (> about 2.5 pm) and fine particles (< about 2.5 pm). Sources of carbon-containing particles are varied and include resuspended soil particles, pollen, plant waxes, etc. in the coarse fraction, and soot particles, sorbed organics including PAHs, and secondary aerosols resulting from... 

The impact of secondary aerosols on indirect radiative forcing is the most variable and is the least understood [3]. The reasons why the indirect effect of secondary aerosols is so difficult to describe is that it depends upon [1] (1) a series of molecular-microphysical processes that connect aerosol nucleation to cloud condensation nuclei to cloud drops and then ultimately to cloud albedo and (2) complex cloud-scale dynamics on scales of 100-1000 km involve a consistent matching of multiple spatial and time scales and are extremely difficult to parameterize and incorporate in climate models. Nucleation changes aerosol particle concentrations that cause changes in cloud droplet concentrations, which in turn, alter cloud albedo. Thus, macro-scale cloud properties that influence indirect forcing result from both micro-scale and large-scale dynamics. To date, the micro-scale chemical physics has not received the appropriate attention. 

Aerosols sea salt, dust, primary and secondary particles of anthropogenic and natural origin. Some aerosol particle components warm up and others cool down the air. 

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