Diurnal variations of organic molecular tracers and stable carbon isotopic composition in atmospheric aerosols over Mt. Tai in the North China Plain: An influence of biomass burning
Organic tracer compounds, as well as organic carbon (OC), elemental\ncarbon (EC), water-soluble organic carbon (WSOC), and stable carbon\nisotope ratios (delta C-13) of total carbon (TC) have been investigated\nin aerosol samples collected during early and late periods of the Mount\nTai eXperiment 2006 (MTX2006) field campaign in the North China Plain.\nTotal solvent-extractable fractions were investigated by gas\nchromatography/mass spectrometry. More than 130 organic compounds were\ndetected in the aerosol samples. They were grouped into twelve organic\ncompound classes, including biomass burning tracers, biogenic primary\nsugars, biogenic secondary organic aerosol (SOA) tracers, and\nanthropogenic tracers such as phthalates, hopanes and polycyclic\naromatic hydrocarbons (PAHs). In early June when the field burning\nactivities of wheat straws in the North China Plain were very active,\nthe total identified organics (2090 +/- 1170 ng m(-3)) were double those\nin late June (926 +/- 574 ng m(-3)). All the compound classes were more\nabundant in early June than in late June, except phthalate esters, which\nwere higher in late June. Levoglucosan (88-1210 ng m(-3), mean 403 ng\nm(-3)) was found as the most abundant single compound in early June,\nwhile diisobutyl phthalate was the predominant species in late June.\nDuring the biomass-burning period in early June, the diurnal trends of\nmost of the primary and secondary organic aerosol tracers were\ncharacterized by the concentration peaks observed at mid-night or in\nearly morning, while in late June most of the organic species peaked in\nlate afternoon. This suggests that smoke plumes from biomass burning can\nuplift the aerosol particulate matter to a certain altitude, which could\nbe further transported to and encountered the summit of Mt. Tai during\nnighttime. On the basis of the tracer-based method for the estimation of\nbiomass-burning OC, fungal-spore OC and biogenic secondary organic\ncarbon (SOC), we estimate that an average of 24% (up to 64 %) of the\nOC in the Mt. Tai aerosols was due to biomass burning in early June,\nfollowed by the contribution of isoprene SOC (mean 4.3 %). In contrast,\nisoprene SOC was the main contributor (6.6 %) to OC, and only 3.0% of\nthe OC was due to biomass burning in late June. In early June, delta\nC-13 of TC (-26.6 to -23.2 %, mean -25.0 %) were lower than those\n(-23.9 to -21.9 %, mean -22.9 %) in late June. In addition, a strong\nanti-correlation was found between levoglucosan and delta C-13 values.\nThis study demonstrates that crop-residue burning activities can\nsignificantly enhance the organic aerosol loading and alter the organic\ncomposition and stable carbon isotopic composition of aerosol particles\nin the troposphere over the North China Plain.