Characteristics and source identification of fine particulate n-alkanes in Beijing, China

Ambient particulate n-alkanes were determined for fine particle （PM2.5） samples collected from Sep 2003 to July 2004 in Beijing, China. The average concentration of total n-alkanes （∑n-alkanes） from Cll to C34 was 425.72 ng/m^3, ranged from 7.02 to 2893.28 ng/m^3. The concentration distributions of n-alkanes homologues in this study exhibited peaks at C21 and C29 in heating season, and C29 in non-heating season. The average carbon preference index （CPI） value was 1.88 in the range of 1.18-3.88. The maximum CPI in summer indicated the contribution of biogenic origins such as plant wax; while the minimum CPI value in winter was probably a result of fossil fuel combustion. Preliminary estimation from these results showed that 59% of the n-alkanes in PM2.5 in Beijing summer originated from plant wax, while 74%-88% was from fossil fuel combustion in other three seasons. Source estimation was further performed using principal component analysis method. Two major components were yielded accounting for 57.3% and 30.9% of the total variance, which presented the fossil fuel and biogenic contribution, respectively.

Variability in pattern and hydrogen isotope composition(δ^(2)H)of long-chain n-alkanes of surface soils and its relations to climate and vegetation characteristics:A meta-analysis

The average chain length(ACL),carbon preference index(CPI),and hydrogen isotope composition(δ^(2)H)of long-chain n-alkanes in sediments have been used to retrieve information about the paleoclimate.Despite their importance as in-between media from leaves to sediments,n-alkanes of surface soils have not been systematically analyzed at large scale.Such an investigation of the spatial variation of n-alkane properties in soil and their dependence on climatic and botanic(e.g.,vegetation type)factors could provide a rationale for a better estimation of the past environment.We synthesized the patterns andδ^(2)H of long-chain n-alkanes in soil(δ^(2)H_(n-alkanes))with regard to vegetation types(cropland,grassland,shrubland,and woodland)and environmental factors using data from peer-reviewed papers.Our results showed that the ACL and CPI of soil C_(27)–C_(33) n-alkanes were not suitable indicators for differentiating vegetation types at large scale;instead,ACL significantly correlated with water conditions such as mean annual precipitation(MAP)and Palmer drought severity index(PDSI),and CPI significantly correlated with temperature without significant influence of vegetation type.The variation(i.e.,standard deviation)of fractionation between theδ^(2)H values in annual precipitation and in soil n-alkanes(ε_(rain-soil))was smaller than that reported in leaves;therefore,soils were better suited to quantifying the general growing conditions of plants at a certain site.The fractionationε_(rain-soil)correlated with climatic conditions as described by the PDSI and relative humidity(RH).This correlation agreed with the change in leaf water enrichment with changing RH taken from the literature and was independent of the vegetation type at large scale.This meta-analysis may provide useful information for the variations of the patterns andδ^(2)H_(n-alkanes) values in surface soils.