Primary and secondary organics in tropical Amazonian rainforest aerosols: Chiral analysis of 2-methyltetrols
This work presents the application of a newly developed method to facilitate the distinction between primary and secondary organic compounds in ambient aerosols based on their chiral analysis. The organic constituents chosen for chiral analysis are the four stereomers of the 2-methyltetrols, (2R,3S)- and (2S,3R)- methylerythritol and (2S,3S)- and (2R,3R)- methylthreitol. Ambient PM10 aerosol samples were collected between June 2008 and June 2009 near Manaus, Brazil, in a remote tropical rainforest environment of central Amazonia. The samples were analyzed for the presence of these four stereomers because qualitatively, in a previous study, they have been demonstrated to have partly primary origins. Thus the origin of these compounds may be primary and secondary from the biosynthesis and oxidation processes of isoprene within plants and also in the atmosphere. Using authentic standards, the quantified concentrations were in average 78.2 and 72.8 ng m-3 for (2R,3S)- and (2S,3R)- methylerythritol and 3.1 and 3.3 ng m-3 for (2S,3S)- and (2R,3R)- methylthreitol during the dry season and 7.1, 6.5, 2.0, and 2.2 ng m-3 during the wet season, respectively. Furthermore, these compounds were found to be outside the confidence interval for racemic mixtures (enantiomeric fraction, Ef = 0.5 -0.01) in nearly all the samples, with deviations of up to 32 % (Ef = 0.61) for (2R,3S)-methylerythritol and 47 % (Ef = 0.65) for (2S,3S)-methylthreitol indicating (99% confidence level) biologically-produced 2-methyltetrols. The minimum primary origin contribution ranged between 0.19 and 29.67 ng m-3 for the 2-methylerythritols and between 0.15 and 1.2 ng m-3 for the 2-methylthreitols. The strong correlation of the diatereomers (racemic 2-methylerythritol and 2-methylthreitol) in the wet season implied a secondary origin. Assuming the maximum secondary contribution in the dry season, the secondary fraction in the wet season was 81-99 % and in the dry season, 10 - 95 %. Nevertheless, from the total 2-methyltetrol mass, the secondary mass represented 31 % whereas the primary 69 %. These results could have been expected for PM10 aerosols and might be different for fine particles at the same site. In addition, correlations with isoprene emission estimates for this site only showed an anti-correlation with 2-methylthreitol suggesting their direct emission from biological activity. The present study reinforces the importance of the analysis of chiral organic compounds to correctly assess the contribution of primary biogenic emissions and isoprene oxidation products to biogenic secondary organic aerosol.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1158975
- Report Number(s):
- PNNL-SA-99454
- Journal Information:
- Environmental Science Processes & Impacts, 16(6):1413-1421, Journal Name: Environmental Science Processes & Impacts, 16(6):1413-1421
- Country of Publication:
- United States
- Language:
- English
Similar Records
Natural and Anthropogenically Influenced Isoprene Oxidation in Southeastern United States and Central Amazon
Seasonality of isoprenoid emissions from a primary rainforest in central Amazonia