Aerosols affect environment at the local, regional, and global levels. At the local level, aerosols are now becoming recognized as a significant health problem, especially in regard to respiratory illnesses, including asthma (Dockery et al., 1993). At global scale, atmospheric aerosols influence climate in two main ways, referred to as direct forcing and indirect forcing (Charlson et al., 1992). In the direct forcing mechanism, aerosols reflect sunlight back to space, thus cooling the planet. The indirect effect involves aerosol particles acting as (additional) cloud condensation nuclei, spreading the cloud's liquid water over smaller droplets. This makes clouds more reflective and longer lasting.

Atmospheric particles are a complex mixture of many species derived from various sources including direct emissions and secondary carbon produced by oxidation. Thus, a deep understanding of their chemical composition is necessary if the source identification is attempted with the purpose of pollution control or abatement. Organic compounds of direct biogenic and anthropogenic origin often represent cumulatively an important fraction, up to 40%, of total particulate matter mass, while individual concentrations range from few picograms up to hundreds of nanograms per cubic meter. Anthropogenic emissions include fossil fuel (diesel and gasoline) combustion from mobile and stationary sources, biomass burning (forest fires, landfills, agricultural activities, and incinerators), and natural gas, wood, and coal combustion. Wind erosion of leaf epicuticular waxes, vegetation debris, microbial degradation, and volcanoes eruption are considered the most important natural sources. The organic compounds associated with particles have been chemically characterized in several studies and comprise: «-alkenes, carbox-ylic and dicarboxylic acids, carbonyls, steroids, aromatic compounds, etc. (Yassaa et al., 2005 and references therein). Among minor components found in ambient aerosols, polycyclic aromatic hydrocarbons (PAHs) are recognized to play a key role with respect to air quality, because they include potent carcinogenic and/or mutagenic compounds. Most PAHs are released by combustion processes applied by man to industrial technologies like energy or steel generation, vehicle and machine engine operation, mineral/crude oil extraction and petroleum refining processes, domestic heating and food cooking, waste/refuse incineration, and smocking.

Algiers (latitude 36° 42' N, longitude 3° 13' E), the capital of Algeria, is one of the largest cities in the North Africa. The city is located in the North of the country, facing the Bay of the Mediterranean Sea. It is the largest city of Algeria, developing over an area of 273 km2. It is the political, economic, and cultural center of the country and is one of the leading ports of North Africa. Nowadays, Algiers is experiencing a rapid urbanization so that its population is approaching six million inhabitants (Statistics, 2006), that is around 20% of the total Algerian population. Starting from the end of last century, the huge migration of peoples to Algiers, combined with the opening of economy to foreign market adopted by the Government, induced the fast increase in traffic circulation which adversely impacted the air quality in many urban areas of Algiers. As a result, large amounts of both volatile and particulate organic compounds could be found and determined in Algiers city.

This chapter presents an overview of the aerial concentration behaviors and seasonal and annual variations of organic compounds comprising «-alkenes, poly-nuclear aromatic hydrocarbons (PAH) and their nitrated derivatives (N-PAH), and their major contributing sources in Algiers. The data set obtained through the investigations conducted from 1998 to 2006 in different locations in Algiers city characterized by different features, urban, industrial, and waste landfill provides useful information for establishing effective control measures to reduce organic pollution in Algiers.

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