Results and Discussion 4231 wAlkenes

The season averaged concentrations of individual «-alkanes found at both in downtown Algiers (1998-1999 and 2005-2006) and waste landfill of Oued Smar (1998-1999 and 2002-2003) are listed in Table 42.1. The «-alkanes concentrations in the cold time were always higher than in the warm one at both sites. This seems to be in good agreement with the general evolution of meteorology dominating the Algiers region, although the nature of incinerated waste could influence to some extent the seasonal variability in Oued Smar. Indeed, the inversion of temperature at the low troposphere is very frequent in winter over the Algiers region and prevents the dispersion of the pollutants, so they accumulate over the earth surface layer, while the low ambient temperature shifts the partition of semi-volatile species toward condensed phase.

The «-alkanes concentrations measured in downtown Algiers in 2005-2006 were much higher than those recorded in 1998-1999. This is mostly due to the fast increase in traffic circulation experienced recently in Algiers city in addition to other factors described earlier in the first section. The concentrations of «-alkanes measured recently in Algiers (2005-2006) were similar to those reported for the industrialized area of Prato (Italy) (37-205 ng m-3) (Cincinelli et al., 2003), but lower than those measured in New Delhi (India) (138-598 ng.m-3) (Sharma et al., 2003) and Qingdao (China) (53-371 ng m-3) (Guo et al., 2003).

Table 42.1 Seasonal average «-alkanes concentrations (ng m 3 of air) in downtown Algiers and waste landfill (sum. means summer and wint. means winter)._

Site

Downtown Algiers

Waste landfill

Year

1998-

-1999

2005-2006

1998-

-1999

2005-

2006

Compound

Sum.

Wint.

Sum.

Wint.

Sum.

Wint.

Sum.

Wint.

«-C16

0.1

5

0.1

5

0.1

5

0.1

5

«-C17

0.5

14.9

0.5

14.9

0.5

14.9

0.5

14.9

«-C18

2.5

12.2

2.5

12.2

2.5

12.2

2.5

12.2

«-Ci9

1.6

9.8

1.6

9.8

1.6

9.8

1.6

9.8

«-C20

2.9

10.9

2.9

10.9

2.9

10.9

2.9

10.9

«-C21

5.7

7.5

5.7

7.5

5.7

7.5

5.7

7.5

«-C22

8.6

8.9

8.6

8.9

8.6

8.9

8.6

8.9

«-C23

9.5

5.2

9.5

5.2

9.5

5.2

9.5

5.2

«-C24

7.3

5.8

7.3

5.8

7.3

5.8

7.3

5.8

«-C25

4.4

3.9

4.4

3.9

4.4

3.9

4.4

3.9

«-C26

2.8

2.7

2.8

2.7

2.8

2.7

2.8

2.7

«-C27

3.1

2.7

3.1

2.7

3.1

2.7

3.1

2.7

«-C28

1.2

1.9

1.2

1.9

1.2

1.9

1.2

1.9

«-C29

3.4

1.4

3.4

1.4

3.4

1.4

3.4

1.4

«-C30

0.5

0.8

0.5

0.8

0.5

0.8

0.5

0.8

«-C31

0.8

0.6

0.8

0.6

0.8

0.6

0.8

0.6

Total

55

94

55

94

55

94

55

94

CPI25

2

1.2

2

1.2

2

1.2

2

1.2

The whole «-alkanes contents (X«-C16 to «-C31: 1192 and 5787 ng m"3 in warm and cold seasons, respectively) measured in waste landfill of Oued Smar in 2002-2003 were compared with those recorded at the same site during the summer 1998 and winter 1999 (X«-C16 to «-C31: 82 and 401 ng m"3 , respectively) (see Table 42.1). The new recordings were 14 times higher than those previously reported. This unexpected increase in the concentrations would be explained by three assumptions: (1) the waste composting procedures undertaken by the Authorities to improve the air quality are not respected or badly concretized in the field; (2) these procedures are applied only in small part of the landfill; and (3) severe multiplication of the quantities of waste amounts deposited and burnt in the Oued Smar landfill passed over any composting procedure operated. It is worth to remark, at this respect, that population and human activities in the Algiers region are both rapidly increasing that leads to the concurrent generation of garbage and refuses. In conclusion, at least two main sources are promoting the occurrence of «-alkanes in the atmosphere of Oued Smar, the former quite unchanging in composition and possibly modulated in amount with year time, and the latter changing in composition, and certainly modulated in amount with year time.

To distinguish the role played by natural sources for the presence of «-alkanes in airborne particles we applied the Carbo« Prefere«ce I«dex (CPI) computation. The CPI rate was calculated through the following formula: CPI 25 = % X[ (C 24 + C 26 + C 28 + C 30 )/(C 25 + C 27 + C 29 + C 3l) + (C 26 + C

28 + ^ 30 + C 32)/(C 27 T <-- 29 + <-- 31 +C 33)]

where the subscript "25" indicates the «-pentacosane homologue is chosen as odd-carbon-numbered lower end point (this assumption allows to reduce the uncertainty related to partial volatility of compounds). According to technical literature (Rogge et al., 1993), the CPI25 rate allows to assess the plant wax contribution versus petroleum-derived fuels to aliphatic contents in aerosols: in fact, CPI25 values close to 1 are characteristic of mineral oil burning, whereas high figures (up to 10) are associated with plant wax release. Since the CPI25 rate remained < 1 over the most of the time at both investigated sites, the predominance of anthropogenic source was confirmed in Algiers city area.

In conclusion, the «-alkanes pattern observed in downtown Algiers was similar to that of motor vehicular exhaust emissions, allowing us to identify the main source of carbon particles there. Stocking and burning of several kinds of materials including biomass and refuses, i.e., plants, foodstuffs, animals, and plastics, caused the huge presence of «-alkanes in the aerosols at the Oued Smar site. The air contamination consequent from anthropic activities appeared more severe at Oued Smar than in downtown Algiers.

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