Isoprene-derived epoxydiols (IEPOX) are identified in ambient aerosol samples for the first time, together with other previously identified isoprene tracers (i.e., 2-methyltetrols, 2-methylglyceric acid, C(5)-alkenetriols, and organosulfate derivatives of 2-methyltetrols). Fine ambient aerosol collected in downtown Atlanta, GA and rural Yorkville, GA during the 2008 August Mini-Intensive Gas and Aerosol Study (AMIGAS) was analyzed using both gas chromatography/quadrupole mass spectrometry (GC/MS) and gas chromatography/time-of-flight mass spectrometry (GC/TOFMS) with prior trimethylsilylation. Mass concentrations of IEPOX ranged from approximately 1 to 24 ng m(-3) in the aerosol collected from the two sites. Detection of particle-phase IEPOX in the AMIGAS samples supports recent laboratory results that gas-phase IEPOX produced from the photooxidation of isoprene under low-NO(x) conditions is a key precursor of ambient isoprene secondary organic aerosol (SOA) formation. On average, the sum of the mass concentrations of IEPOX and the measured isoprene SOA tracers accounted for about 3% of the organic carbon, demonstrating the significance of isoprene oxidation to the formation of ambient aerosol in this region.
Chemical tracer methods for determining contributions to primary organic aerosol (POA) are fairly well established, whereas similar techniques for secondary organic aerosol (SOA), inherently complicated by time-dependent atmospheric processes, are only beginning to be studied. Laboratory chamber experiments provide insights into the precursors of SOA, but field data must be used to test the approaches. This study investigates primary and secondary sources of organic carbon (OC) and determines their mass contribution to particulate matter 2.5 microm or less in aerodynamic diameter (PM2.5) in Southeastern Aerosol Research and Characterization (SEARCH) network samples. Filter samples were taken during 20 24-hr periods between May and August 2005 at SEARCH sites in Atlanta, GA (JST); Birmingham, AL (BHM); Centerville, AL (CTR); and Pensacola, FL (PNS) and analyzed for organic tracers by gas chromatography-mass spectrometry. Contribution to primary OC was made using a chemical mass balance method and to secondary OC using a mass fraction method. Aerosol masses were reconstructed from the contributions of POA, SOA, elemental carbon, inorganic ions (sulfate [SO4(2-)], nitrate [NO3-], ammonium [NH4+]), metals, and metal oxides and compared with the measured PM2.5. From the analysis, OC contributions from seven primary sources and four secondary sources were determined. The major primary sources of carbon were from wood combustion, diesel and gasoline exhaust, and meat cooking; major secondary sources were from isoprene and monoterpenes with minor contributions from toluene and beta-caryophyllene SOA. Mass concentrations at the four sites were determined using source-specific organic mass (OM)-to-OC ratios and gave values in the range of 12-42 microg m(-3). Reconstructed masses at three of the sites (JST, CTR, PNS) ranged from 87 to 91% of the measured PM2.5 mass. The reconstructed mass at the BHM site exceeded the measured mass by approximately 25%. The difference between the reconstructed and measured PM2.5 mass for nonindustrial areas is consistent with not including aerosol liquid water or other sources of organic aerosol.
The sampling artifacts (both positive and negative) and the influence of thermal-optical methods (both charring correction method and the peak inert mode temperature) on the split of organic carbon (OC) and elemental carbon (EC) were evaluated in Beijing. The positive sampling artifact constituted 10% and 23% of OC concentration determined by the bare quartz filter during winter and summer, respectively. For summer samples, the adsorbed gaseous organics were found to continuously evolve off the filter during the whole inert mode when analyzed by the IMPROVE-A temperature protocol. This may be due to the oxidation of the adsorbed organics during sampling (reaction artifact) which would increase their thermal stability. The backup quartz approach was evaluated by a denuder-based method for assessing the positive artifact. The quartz-quartz (QBQ) in series method was demonstrated to be reliable, since all of the OC collected by QBQ was from originally gaseous organics. Negative artifact that could be adsorbed by quartz filter was negligible. When the activated carbon impregnated glass fiber (CIG) filter was used as the denuded backup filter, the denuder efficiency for removing gaseous organics that could be adsorbed by the CIG filter was only about 30%. EC values were found to differ by a factor of about two depending on the charring correction method. Influence of the peak inert mode temperature was evaluated based on the summer samples. The EC value was found to continuously decrease with the peak inert mode temperature. Premature evolution of light absorbing carbon began when the peak inert mode temperature was increased from 580 to 650 degrees C; when further increased to 800 degrees C, the OC and EC split frequently occurred in the He mode, and the last OC peak was characterized by the overlapping of two separate peaks. The discrepancy between EC values defined by different temperature protocols was larger for Beijing carbonaceous aerosol compared with North America and Europe, perhaps due to the higher concentration of brown carbon in Beijing aerosol.
Measurement of carbonaceous aerosols is complicated by positive and negative artifacts. An organic denuder with high efficiency for removing gaseous organics is an effective approach to eliminate the positive artifact, and it is a precondition for the accurate determination of SVOC by an adsorbent backup filter. Evaluations of different configurations of the organic denuder, and SVOC determined by different denuder-based samplers, both integrated and semi-continuous, are reviewed. A new equation for determination of the denuder efficiency is estimated, considering the efficiency of removing both the gaseous organics that could be adsorbed by the quartz and the gaseous passing through the quartz that could be subsequently adsorbed by the backup adsorbent filter. The origin of OC on the backup quartz filter, behind either quartz or Teflon filter, is quantitatively evaluated by the denuder-based method based on the data published. The backup-OC is shown to be dominated by either gaseous organics passing through the front filter or the evaporated particulate organic carbon depending on the sampling environment.
Biomass burning is a major and growing contributor to particulate matter with an aerodynamic diameter less than 2.5 μm (PM2.5). Such impacts (especially individual impacts from each burning source) are quantified using the Community Multiscale Air Quality (CMAQ) Model, a chemical transport model (CTM). Given the sensitivity of CTM results to uncertain emission inputs, simulations were conducted using three biomass burning inventories. Shortcomings in the burning emissions were also evaluated by comparing simulations with observations and results from a receptor model. Model performance improved significantly with the updated emissions and speciation profiles based on recent measurements for biomass burning: mean fractional bias is reduced from 22% to 4% for elemental carbon and from 18% to 12% for organic matter; mean fractional error is reduced from 59% to 50% for elemental carbon and from 55% to 49% for organic matter. Quantified impacts of biomass burning on PM2.5 during January, March, May, and July 2002 are 3.0, 5.1, 0.8, and 0.3 μg m−3 domainwide on average, with more than 80% of such impacts being from primary emissions. Impacts of prescribed burning dominate biomass burning impacts, contributing about 55% and 80% of PM2.5 in January and March, respectively, followed by land clearing and agriculture field burning. Significant impacts of wildfires in May and residential wood combustion in fireplaces and woodstoves in January are also found.
A comprehensive comparison of positive matrix factorization (PMF) and molecular marker-based chemical mass balance (CMB-MM) modeling on PM2.5 source contributions was conducted for particulate matter measurements taken at Jefferson Street, Atlanta, Georgia (JST). The datasets used in each type of receptor modeling were different: CMB-MM used data of primarily organic tracers plus a couple elements measured from 51 24-h PM2.5 samples collected in July 2001 and January 2002. While for PMF, with elements, ions, five gaseous components, and eight temperature-resolved carbon fractions as the input data, both source profiles and contributions were resolved from a total of 932 daily PM2.5 samples covering a 3-year period between January 2000 and December 2002. The model results for the overlapping periods (July 2001 and January 2002) were extracted for comparison. Seven primary sources and three secondary sources were resolved by CMB-MM, while a total of nine primary and secondary factors were resolved by PMF. On average, 107% and 85% of PM2.5 mass were explained by CMB-MM and PMF, respectively, with secondary aerosols handled differently in the above two methods. Four similar sources were resolved by both methods, with good correlation for road dust, but fair for gasoline exhaust and wood combustion. The CMB-MM diesel exhaust has very poor correlation with the PMF resolved diesel exhaust. However, the CMB-MM combined mobile source has improved correlation with the PMF result as compared with the diesel exhaust source. If only the winter data were included, the CMB-MM combined mobile source shows enhanced correlation with the PMF combined source, as compared with the single source of diesel exhaust or gasoline exhaust.
One year of high-volume PM2.5 filter samples were collected from 2004 to 2005 at one rural site and three urban sites in the Southeastern Aerosol Research and Characterization (SEARCH) network. These filters were analyzed for both organic tracers and carbon isotopes. Sources for primary carbon were previously apportioned based on molecular marker-based chemical mass balance modeling (CMB-MM). In this study, these primary sources were further classified into two categories as having fossil and contemporary origins. 14C data were used to estimate the relative contributions of fossil and contemporary contents in total carbon (TC). Combined these two sets of independent results, fossil and contemporary contributions to secondary carbon source, which was estimated by the unexplained OC in CMB-MM, were calculated. The fossil secondary organic carbon (SOCF) and the contemporary secondary organic carbon (SOCC) ranged from 0.56 to 3.20 microgC/m3 and 0.82 to 4.09 microgC/m3, respectively. SOCF was higher at urban sites and exhibited small seasonal variation at all sites, probably resulting from higher fossil precursor emissions in urban areas. In contrast, SOCC was higher at the rural site and exhibited obvious seasonal variation at all sites. During the whole year SOCF was the major secondary organic carbon (SOC) contributor at the urban sites, while SOCC dominated SOC at the rural site. In summer isoprene-derived SOC showed a large contribution to SOCC and exhibited significant positive correlation with SOCC, indicating the importance of isoprene-derived secondary organic aerosol (SOA) formation during summer. It is interesting to note that the secondary items, including SOCF, SOCC, secondary sulfate, and secondary ammonium, exhibited significant correlations between the monitoring sites, suggesting the regional impact of secondary aerosol in the southeastern United States.
For the time being, Integrated Optics is able to produce a range of devices able of efficiently modulating phase, amplitude and frequency of guided waves in single mode structures implemented at the surface of active materials such as Lithium Niobate. In most of the cases, their basic principle relies on the interference pattern of two guided waves and the classical implementations of such modulators were mainly related to COBRA switch type directional couplers or to MACH ZEHNDER type interferometers. Only very recently a structure combining the coupled waveguides of a COBRA and the Y junction of the MACH ZEHNDER interferometer was designed. This paper is an analysis of the switching characteristics of this Y-fed directional coupler and of its high frequency modulation properties.
Organic compounds including alkanes, fatty acids, and polycyclic aromatic hydrocarbons (PAHs) and trace and major elements in four size fractions (< 0.49 mu m, 0.49-0.95 mu m, 0.95-2.5 mu m, and 2.5-10 mu m) collected from June 1998 to January 1999 in Hong Kong were physically and chemically characterized by scanning electron microscope (SEM), gas chromatography/mass spectrometry (GC-MS), and inductively coupled plasma/mass spectrometry (ICP-MS) to study their size distributions, seasonal variations, and sources. SEM micrographs show that abundances and shapes of particles in each size fraction exhibit distinct difference between wet and dry seasons. Solvent extractable organic compounds (SEOC) investigated in this study were significantly enriched in fine particulate matter (PM2.5) since 97\% of PAH, 88\% of alkane, and 69\% of fatty acids in PM10 were actually from PM2.5. The pollution elements and SEOC showed a change from a maxima in the finest fraction (< 0.49 mm) in the wet season, to an obvious increase in the 0.49-2.5 mu m fraction in September and October, and to a maxima in the finest fraction again in November and December. This corresponds to a change from a strong local emission from pollution sources, to possibly aged materials in the transition period of Asian monsoon, and to the pollution emissions dominated by those transported from the continent. The distinct difference of particle size distributions between wet and dry seasons suggests that the health effects of particles in Hong Kong may be different in those seasons.
During the 2003 Chinese Arctic Research Expedition from the Bohai Sea to the high Arctic (37–80°N) aboard the icebreaker Xuelong (Snow Dragon), air samples were collected using a modified high-volume sampler that pulls air through a quartz filter and a polyurethane foam plug (PUF). These filters and PUFs were analyzed for particulate phase and gas phase polycyclic aromatic hydrocarbons (PAHs), respectively, in the North Pacific Ocean and adjacent Arctic region. The ∑PAHs (where ∑=15 compounds) ranged from undetectable level to 4380pgm−3 in the particulate phase and 928–92600pgm−3 in the gas phase, respectively. A decreasing latitudinal trend was observed for gas-phase PAHs, probably resulting from temperature effects, dilution and decomposition processes; particulate-phase PAHs, however, showed poor latitudinal trends, because the effects of temperature, dilution and photochemistry played different roles in different regions from middle-latitude source areas to the high latitudes. The ratios of PAH isomer pairs, either conservative or sensitive to degradation during long-range transport, were employed to interpret sources and chemical aging of PAHs in ocean air. In this present study the fluoranthene/pyrene and indeno[123-cd]pyrene/benzo[ghi]pyrene isomer pairs, whose ratios are conservative to photo-degradation, implies that biomass or coal burning might be the major sources of PAHs observed over the North Pacific Ocean and the Arctic region in the summer. The isomer ratios of 1,7/(1,7+2,6)-DMP (dimethylphenanthrene) and anthracene/phenanthrene, which are sensitive to aging of air masses, not only imply chemical evolving of PAHs over the North Pacific Ocean were different from those over the Arctic, but reveal that PAHs over the Arctic were mainly related to coal burning, and biomass burning might have a larger contribution to the PAHs over the North pacific ocean.
Hong Kong's persistent unhealthy level of fine particulate matter is a current public health challenge, complicated by the city being located in the rapidly industrializing Pearl River Delta Region of China. While the sources of the region's fine particulate matter (PM2.5) are still not well understood, this study provides new source information through ground measurements and statistical analysis of 24 elements associated with particulate matter collected on filters. Field measurements took place over 4 months (October 2002, December 2002, March 2003, and June 2003) at seven sites throughout the Pearl River Delta, with three sites located in Hong Kong and four sites in the neighboring province, Guangdong. The 4-month average element concentrations show significant variation throughout the region, with higher levels of nearly every species seen among the northern Guangdong sites in comparison to Hong Kong. The high correlation (Pearson r>0.8) and similar magnitudes of 11 species (Al, Si, S, K, Ca, Mn, Fe, Zn, Br, Rb, and Pb) at three contrasting sites in Hong Kong indicate that sources external to Hong Kong dominate the regional levels of these elements. Further correlative analysis compared Hong Kong against potential source areas in Guangdong Province (Shenzhen, Zhongshan, and Guangzhou). Moderate correlation of sulfur for all pairings of Hong Kong sites with three Guangdong sites in developed areas (average Pearson r of 0.52–0.94) supports the importance of long-distance transport impacting the region as a whole, although local sources also clearly impact observed concentrations. Varying correlative characteristics for zinc when Hong Kong sites are paired with Shenzhen (average r=0.86), Guangzhou (average r=−0.65) and Zhongshan (average r=0.45) points to a source area located south of Guangzhou and locally impacting Zhongshan. The concentration distribution and correlative characteristics of bromide point to sources located within the Pearl River Delta, but the specific location is yet inconclusive. Uniquely poor correlation of eight species (Al, Si, K, Ca, Mn, Fe, Rb, and Pb) for the pairing of Hong Kong sites with Guangzhou, in addition to the relatively higher concentrations measured at Guangzhou, indicates a significant regional impact due to land development and industrial activities in the Guangzhou vicinity.
Polycyclic aromatic hydrocarbons (PAHs) in two 210Pb dated sediment cores from the coastal East China Sea, strongly influenced by the discharge from the Yangtze River, were determined to help to reconstruct the economic development over the past century in East China. The variations in PAH concentrations and fluxes in the sediment cores were primarily due to energy structure change, severe floods and dam construction activities. The impact on PAHs by the river discharge overwhelmed the atmospheric depositions. The profiles of PAH fluxes and concentrations as well as compositions in the cores revealed the transformation from an agricultural economy to an industrial one especially after the 1990s' in the region. PAHs in the study area were dominated by pyrolytic sources.
To assess the contribution of sources to fine particulate organic carbon (OC) at four sites in North Carolina, USA, a molecular marker chemical mass balance model (MM-CMB) was used to quantify seasonal contributions for 2 years. The biomass burning contribution at these sites was found to be 30–50% of the annual OC concentration. In order to provide a better understanding of the uncertainty in MM-CMB model results, a biomass burning profile sensitivity test was performed on the 18 seasonal composites. The results using reconstructed emission profiles based on published profiles compared well, while model results using a single source test profile resulted in biomass burning contributions that were more variable. The biomass burning contribution calculated using an average regional profile of fireplace emissions from five southeastern tree species also compared well with an average profile of open burning of pine-dominated forest from Georgia. The standard deviation of the results using different source profiles was a little over 30% of the annual average biomass contributions. Because the biomass burning contribution accounted for 30–50% of the OC at these sites, the choice of profile also impacted the motor vehicle source attribution due to the common emission of elemental carbon and polycyclic aromatic hydrocarbons. The total mobile organic carbon contribution was less effected by the biomass burning profile than the relative contributions from gasoline and diesel engines.