Atmospheric benzenoid emissions from plants rival those from fossil fuels.

Despite the known biochemical production of a range of aromatic compounds by plants and the presence of benzenoids in floral scents, the emissions of only a few benzenoid compounds have been reported from the biosphere to the atmosphere. Here, using evidence from measurements at aircraft, ecosystem, tree, branch and leaf scales, with complementary isotopic labeling experiments, we show that vegetation (leaves, flowers, and phytoplankton) emits a wide variety of benzenoid compounds to the atmosphere at substantial rates. Controlled environment experiments show that plants are able to alter their metabolism to produce and release many benzenoids under stress conditions. The functions of these compounds remain unclear but may be related to chemical communication and protection against stress. We estimate the total global secondary organic aerosol potential from biogenic benzenoids to be similar to that from anthropogenic benzenoids (~10 Tg y(-1)), pointing to the importance of these natural emissions in atmospheric physics and chemistry.

Particle size distribution of n-alkanes and polycyclic aromatic hydrocarbons (PAHS) in urban and industrial aerosol of Algiers, Algeria.

The distribution of ambient air n-alkanes and polycyclic aromatic hydrocarbons (PAHs) associated to particles with aerodynamic diameters lesser than 10 µm (PM(10)) into six fractions (five stages and a backup filter) was studied for the first time in Algeria. Investigation took place during September of 2007 at an urban and industrial site of Algiers. Size-resolved samples (<0.49, 0.49-0.95, 0.95-1.5, 1.5-3.0, 3.0-7.2, and 7.2-10 µm) were concurrently collected at the two sampling sites using five-stage high-volume cascade impactors. Most of n-alkanes (~72 %) and PAHs (~90 %) were associated with fine particles ≤ 1.5 µm in both urban and industrial atmosphere. In both cases, the n-alkane contents exhibited bimodal or weakly bimodal distribution peaking at the 0.95-1.5-µm size range within the fine mode and at 7.3-10 µm in the coarse mode. Low molecular weight PAHs displayed bimodal patterns peaking at 0.49-0.95 and 7.3-10 µm, while high molecular weight PAHs exhibited mono-modal distribution with maximum in the <0.49-µm fraction. While the mass mean diameter of total n-alkanes in the urban and industrial sites was 0.70 and 0.84 µm, respectively, it did not exceed 0.49 µm for PAHs. Carbon preference index (~1.1), wax% (10.1-12.8), and the diagnostic ratios for PAHs all revealed that vehicular emission was the major source of these organic compounds in PM(10) during the study periods and that the contribution of epicuticular waxes emitted by terrestrial plants was minor. According to benzo[a]pyrene-equivalent carcinogenic power rates, ca. 90 % of overall PAH toxicity across PM(10) was found in particles ≤ 0.95 µm in diameter which could induce adverse health effects to the population living in these areas.

Chemical characteristics of organic aerosol in Bab-Ezzouar (Algiers). Contribution of bituminous product manufacture.

The organic compositions of atmospheric particulate matter from Bab-Ezzouar (Algiers) have been investigated to assess the air pollution levels suspected to be caused by asphalt product and yeast manufactures. After a medium-volume air sampling, soxhlet extraction, alumina elution and HPLC separation, the extracts were analysed by high-resolution gas chromatography (HRGC) and gas chromatography coupled to mass spectrometry (GC-MS). The composition of n-alkane and polycyclic aromatic hydrocarbons (PAH) fractions reflected the petrogenic origin from the emission of asphalt materials production in addition to vascular plant wax emissions. In contrast, microbial activities seemed to play the main role for the presence of n-alkanoic acids at Bab-Ezzouar. The sole nitrated polycyclic aromatic hydrocarbons (NPAH) observed, i.e., 2-nitrofluoranthene (2NFA), was very likely to arise from gas-phase photochemical reaction of parent PAH in the atmosphere. The total aerial levels ranged from 75 to 206 ng m(-3) for n-alkanes, from 153 to 345 ng m(-3) for n-alkanoic acids and from 44 to 100 ng m(-3) for PAH and NPAH. Although the samples were collected during the hot season, the levels of these pollutants seemed to be important and of environmental concern, especially for PAH species.

Organic aerosols in urban and waste landfill of Algiers metropolitan area: occurrence and sources.

In both downtown Algiers and the waste landfill of Oued Smar, the concentrations of particulate organic compounds comprising n-alkanes, n-alkanoic acids, n-alkan-2-ones, polycyclic aromatic hydrocarbons (PAHs), oxygenated (OPAHs), and nitrated polycyclic aromatic hydrocarbons (NPAHs) in ambient air were measured from May 1998 to February 1999. All the components except OPAHs had a tendency to strongly increase in colder weather. Motor vehicles were found to be the main source of airborne particles in downtown Algiers, while the combustion and pyrolysis processes and bacterial activity seemed to concur to the air pollution at the Oued Smar waste landfill. The biogenic emission, which was restricted to the lighter fraction of the n-alkanes and n-alkanoic acids, appeared to contribute at a lesser extent. The in-situ generation of some OPAHs and NPAHs seemed to contribute to air pollution, especially during the summertime. As expected, the ambient concentrations of NPAHs and OPAHs were lower than those of their parent PAHs. The seasonal variations in ambient NPAH and OPAH concentrations are due partly to fluctuations of precursors including NOx, 03, and OH radicals. In general, the wintertime concentrations of the organic pollutants in Algiers were similar to those measured in Europe and especially over the Mediterranean Basin. Further investigations have been planned in order to obtain a thorough knowledge of the air pollution as well as the organic content of materials burning atthe Oued Smarwaste landfill. In particular, our concern will be addressed to sources of toxic components, to formulate strategies suitable for reducing health risk for the populations living in the region of Algiers.

Trace level determination of enantiomeric monoterpenes in terrestrial plant emission and in the atmosphere using a beta-cyclodextrin capillary column coupled with thermal desorption and mass spectrometry.

For the first time, enrichment on solid sorbents followed by thermal desorption has been used for the determination of the enantiomeric signature of monoterpenes in the gaseous emission of terrestrial plants. A beta-cyclodextrin capillary column has been used for the separation of critical pairs. The temperature program and column loading were optimized for making the accurate quantification of individual enantiomers possible by mass spectrometry. The resolution achieved was sufficient for separating enantiomeric monoterpenes from other biogenic and anthropogenic volatile organic compounds present in air and vegetation emission samples. The method has been applied to the determination of the enantiomeric ratios of monoterpenes in the gaseous emissions of some evergreen plants and in the open atmosphere.

Organic content of particulate matter in the atmosphere of Ouargla City, Algeria.

The particle-bound organic compounds comprising n-alkanes, n-alkanoic monocarboxylic acids, polynuclear aromatic hydrocarbons (PAH) and nitrated polynuclear aromatic hydrocarbons (NPAH) were investigated in ambient air of the Ouargla city area (Algeria) during a short campaign performed in November 1999. The distribution profile of n-alkanes was consistent with the petrogenic origin of aerosols, suggesting that they were related to torching processes of crude oil refuses in the petroleum extraction field located not far from Ouargla. Instead, the presence of n-alkanoic acids of low molecular weight was indicative of microbial activity experienced by the site. PAH levels were low when compared to other polluted areas. The presence of 2-nitrofluoranthene and 2-nitropyrene, which can result from in-situ nitration of fluoranthene and pyrene, was concurrent with the substantial depletion of the most reactive among PAH, suggesting that photochemical processes influence the composition of the Saharian atmosphere.