Nitropolycyclic aromatic hydrocarbons NPAH

The oxidative capacity of the atmosphere of Algiers is mirrored somewhat by the presence of 2-nitrofluoranthene (2-NFA) and 2-nitropyrene (2-NPY) reported in Table 42.3. This finding confirms also the ubiquitous occurrence of these two 2-NPAH in the troposphere, while the absence or rather low levels of 1-nitropyrene which is directly emitted by diesel-powered vehicles and other combustion processes (Ciccioli et al., 1996) supports the idea that photochemistry is the sink way of the reactive PAH, rather than the scarce release from their emission sources.

Table 42.3 Mean 2-nirofluoranthene (2-NFA) and 2-nitropyrene (2-NPY) concentrations (ng m 3 of air) in Algiers compared with those reported in other sites._

Site

2-NFA

2-NPY

Algiers urban area, Algeria

1998-1999

Summer

Winter

2002-2003

Summer

Winter

Oued Smar, Algiers, Algeria

1998-1999

Summer

Winter

2002-2003

Summer

Winter

Bab-Ezzouar, Algiers, Algeria Milan, Italy (Cecinato et al., 1998) Rome, Italy (Cecinato et al., 1998) Naples, Italy (Ciccioli et al., 1996) Montelibretti, Italy (Ciccioli et al., 1996) C.Porziano, Italy (Ciccioli et al., 1996) Barcelona, Spain (Bayona et al., 1994) Madrid, Spain (Ciccioli et al., 1996) Athens, Greece (Marino et al., 2000) Birmingham, UK (Dimashki et al., 2000) Paris, France (Wortham et a., 1990) Vienna, Austria (Schneider et al., 1990) Zabre, Poland (Warzecha, 1993) Claremont, CA, USA (Zielinska et al., 1989) Torrance, CA, USA (Arey et al., 1989) Night-time Daytime

Autumn

Winter

G.G59 G.GG2

G.GG4

G.G46

1.5G

G.55

G.28

G.1G

G.G9

G.G6

G.12

G.G7

G.G9

G.22

G.22

G.3G

G.35

G.41

G.12

G.13

G.G6

G.G2

G.G1

G.G2

G.G2

G.G6

G.G5

As displayed in Table 42.3, the levels of these 2-nitroarenes are somehow comparable to those measured in different sites around the world having different typologies. This suggests that gas-phase reactions were so pronounced that their formation starting from their parent PAH was promoted. In fact, so far it has consistently reported by literature that 2-NFA and 2-NPY are lacking in the direct emissions and their occurrence in the atmosphere can be solely explained by in situ generation through a two-step gas-phase reaction comprising (i) the addition of an OH or NO3 radical at position 1 of the parent PAH, followed by (ii) a further NO2 fixation onto position 2, and (iii) loss of water or nitric acid, giving rise to NPAH derivative. Finally the products formed are rapidly adsorbed onto suspended particles (Ciccioli et al., 1996). The ratio of 2-NFA versus 2-NPY has been used to assess the importance of daytime against nighttime formation mechanisms of nitrated PAH. In this respect, laboratory studies reported (Ciccioli et al., 1996) that ratios close to 10 are representative of OH radical-initiated reactions developing at the light, while figures approaching 100 are related to the formation at the dark, promoted by NO3 radicals. Values of this ratio always below 10 found in Algiers highlight the prevalence of daytime nitration of PAH initiated by OH radicals.

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