Characterization of Particulate-Phase High Molecular Weight Mono-Carbonyls (C# > 5) and Dicarbonyls in Urban Atmosphere of Xi'an, China

An analytical method to quantify particulate-phase high molecular weight mono-carbonyls (C# &gt; 5) and di-carbonyls has been developed by adopting 2,4-dinitrophenylhydrazine (DNPH) derivatization followed by high performance liquid chromatography/ultra-violet (HPLC/UV) detection. Satisfactory reproducibility and precision of the measurements were achieved. This method was applied to measure the carbonyls in PM2.5 collected on quartz-fiber filters, sampled in Xi&#39;an, China, from 2008 to 2009. Nonanaldehyde was the most abundant compound, followed by octanaldehyde, hexanaldehyde and heptaldehyde, accounting for 40%, 20%, 12% and 11% in the total quantified carbonyls. For dicarbonyls, the concentration of methylglyoxal was much higher than that of glyoxal. The seasonal variations of the particulate-phase mono-carbonyls and dicarbonyls were similar to those in the gas-phase, namely winter &gt; autumn &gt; spring &gt; summer (except octanaldehyde). A strong correlation among those carbonyls was observed in winter, resulting from low temperature partitioning, weaker photochemical reaction, and more primary emission sources. In contrast, in summer, vehicle emissions, cooking emissions and photochemical reactions are the major pollution source in Xi&#39;an.</p

Biases in ketone measurements using DNPH-coated solid sorbent cartridges

Biases associated with carbonyl measurement using active air sampling through a 2,4-dinitrophenylhydrazine (DNPH)-coated solid sorbent cartridge following the U.S. EPA Method TO-11A are known but have not been fully investigated. Ketones are less reactive than aldehydes in the derivatization with DNPH, resulting in poor collection efficiency. Field studies and laboratory experiments demonstrate the uncertainties associated with two ketones (i.e., acetone and methyl ethyl ketone [MEK]). Ketone collection efficiencies are inversely related to relative humidity (RH), sample flow rate, and sample duration. Since water is a product in the bidirectional derivatization of carbonyls, the reverse reaction competes with the forward reaction as RH increases. Laboratory experiments demonstrate that similar to 35-80% of the ketones can be lost for RH &gt; 50% with a single DNPH cartridge at a temperature of 22 +/- 2 degrees C. Optimal sampling flow rates and sampling durations under high RH need to be determined in various environments to ensure tolerable collection efficiencies.</p

Seasonal and diurnal variations of mono- and di-carbonyls in Xi'an, China

Seventeen carbonyls in urban ambient air were quantified in summer (June 2009) and winter (January 2010) in an urban site located in Xi&#39;an, China. Formaldehyde, acetaldehyde and acetone were the three most abundant carbonyls in the atmosphere with the concentrations of 6.54 +/- 2.38 ppbv, 2.08 +/- 1.07 ppbv and 2.74 +/- 1.14 ppbv in summer (from 14th to 24th June, 2009), respectively. In winter, the concentrations were 4.46 +/- 1.74 ppbv, 6.52 +/- 3.88 ppbv and 3.87 +/- 2.33 ppbv respectively from 4th January, 2010 to 10th January, 2010. Most carbonyls had higher concentrations in winter than in summer. And majority of the species had higher concentrations in daytime than in nighttime, indicating photochemical oxidation/human activities played an important role in diurnal variation. Formaldehyde/acetaldehyde ratios (F/A) in summer (2.14) was much higher than that in winter (0.47), showing significant effect of photochemical oxidation in the urban air during summer. Acetaldehyde/propionaldehyde (A/P) average ratio was 12.2 in wintertime, implying anthropogenic emission was the major source of carbonyls in Xi&#39;an. In addition, the ratio of acetone to methylglyoxal (A/M) is used to determine the impact of photochemistry in the atmosphere. The average acetone/methylglyoxal ratio (10.3 +/- 2.3) in summer was lower than that in winter (21.3 +/- 5.1) in Xi&#39;an. Strong correlations among some carbonyls imply that they came from the same pollution sources. Formaldehyde and acetaldehyde play a very important role in photochemical smog formation. Methylglyoxal and glyoxal also have significant contribution to ozone formation potential.</p

Characterization and seasonal variations oflevoglucosan in fine particulate matter in Xi’an, China

PM2.5 (particulate matter with an aerodynamic diameter &lt;2.5 mm) samples (n &frac14; 58) collected every sixth day in Xi&rsquo;an, China, from 5 July 2008 to 27 June 2009 are analyzed for levoglucosan (1,6-anhydro-b-D-glucopyranose) to evaluate the impacts of biomass combustion on ambient concentrations. Twenty-four-hour levoglucosan concentrations displayed clear summer minima and winter maxima that ranged from 46 to 1889 ng m 3, with an average of 428 399 ng m 3. Besides agricultural burning, biomass/biofuel combustion for household heating with straws and branches appears to be of regional importance during the heating season in northwestern China. Good correlations (0.70 &lt; R &lt; 0.91) were found between levoglucosan relative to watersoluble K&thorn;, Cl , organic carbon (OC), elemental carbon (EC), and glyoxal. The highest levoglucosan/OC ratio of 2.3% was found in winter, followed by autumn (1.5%). Biomass burning contributed to 5.1&ndash;43.8% of OC (with an average of 17.6 8.4%).</p

Chemical characteristics of PM2.5 and organic aerosol source analysis during cold front episodes in Hong Kong, China

In this study, we investigate the influence of long-range transport (LRT) episodes brought in by cold front on the concentration levels of PM2.5, major aerosol constituents, organic tracers, and PM2.5 source characteristics in Hong Kong, China. PM2.5 samples were collected during January&ndash;March 2004 and January&ndash;March 2005 and analyzed for major constituents and organic tracer species. Synoptic weather conditions and characteristics of common air pollutants were used to categorize the sampling days to three groups, i.e., groups mainly affected by local emissions or regional transport (RT) or cold front LRT. Concentrations of PM2.5 mass and its major constituents during cold-front days were lower than those during RT-dominated periods but higher than those during local emissions-dominated periods. Source apportionment using chemical mass balance (CMB) indicates that vehicular exhaust was a significant primary OC source of mainly local emissions, making average contributions of 1.82, 1.50, and 2.39 &mu;g C m&minus; 3 to OC in the local, LRT, and RT sample groups, respectively. During cold front periods, primary OC concentrations attributable to biomass burning and coal combustion were approximately triple and double, respectively, those during periods dominated by local emissions. Suspended dust, a minor primary OC source (0.24&ndash;0.40 &mu;g C m&minus; 3), also showed increased contribution during cold fronts. The unexplained OC by CMB (i.e., total OC minus apportioned primary OC), an approximate indicator for secondary OC, was a significant fraction of OC (&gt; 48%) and its mass concentration was much higher in the cold front LRT and RT sample groups (6.37 and 9.48 &mu;g C m&minus; 3) than in the local sample group (3.8 &mu;g C m&minus; 3). Source analysis as well as tracer concentration variation shows that biomass burning OC and water soluble organic carbon (WSOC) were correlated, suggesting biomass burning as a significant contributor to WSOC.</p

Chemical characteristics and source apportionment of fine particulateorganic carbon in Hong Kong during high particulate matter episodesin winter 2003

PM2.5 samples were collected at six general stations and one roadside station in Hong Kong in two periods of high particulate matter (PM) in 2003 (27 October&ndash;4 November and 30 November&ndash;13 December). The highest PM2.5 reached 216 &mu;g m&minus;3 during the first high PM period and 113 &mu;g m&minus;3 during the second high PM period. Analysis of synoptic weather conditions identified individual sampling days under dominant influence of one of three types of air masses, that is, local, regional and long‐range transported (LRT) air masses. Roadside samples were discussed separately due to heavy influences from vehicular emissions. This research examines source apportionment of fine organic carbon (OC) and contribution of secondary organic aerosol on high PM days under different synoptic conditions. Six primary OC (POC) sources (vehicle exhaust, biomass burning, cooking, cigarette smoke, vegetative detritus, and coal combustion) were identified on the basis of characteristic organic tracers. Individual POC source contributions were estimated using chemical mass balance model. In the roadside and the local samples, OC was dominated by the primary sources, accounting for more than 74% of OC. In the samples influenced by regional and LRT air masses, secondary OC (SOC), which was approximated to be the difference between the total measured OC and the apportioned POC, contributed more than 54% of fine OC. SOC was highly correlated with water‐ soluble organic carbon and sulfate, consistent with its secondary nature.</p

Quantification of carbonate carbon in aerosol filter samples using a modified thermal/optical carbon analyzer (M-TOCA)

Measurement of carbon dioxide (CO2) gas evolved from acidification is a method to quantify carbonate carbon (CC) in aerosols collected on quartz fiber-filters. This paper describes the installation of an add-on device in a DRI Model 2001 Thermal Optical reflectance (TOR)/Thermal Optical Transmittance (TOT) Carbon Analyzer (M-TOCA) to facilitate a direct CC measurement. In each run, a maximum of 20 filter punches (each of 0.5 cm(2)) were acidified with 1 mL of 20% v/v phosphoric (V) acid in a vial under a 100% helium gas environment. The CO2 evolved was reduced to methane (CH4) and detected by a flame ionization detector (FID). The optimum reaction kinetics were obtained under an operational temperature of 40 degrees C and ultrasonic agitation. Method precisions were +/- 3.5% on average for carbonate standards ranging from 3.0 to 60.0 mu g and +/- 3.8% on average for ambient samples in masses ranging from 0.30 to 56.0 mu g respectively. Method accuracy was on average 91.9%, ranging from 81.4 to 102.1%. Minimum detection limit (MDL) of the M-TOCA method was 0.048 mu g cm(-2), corresponding to an ambient concentration of 0.098 mu g m(-3) for a sampled volume of air of 7.2 m(3). The MDL is &gt;22 times lower than the value obtained using the novel method with a regular TOCA. Comparison studies on standards and ambient samples have demonstrated that the two methods do not yield systematic differences in concentrations of the carbonate. The lower MDL value provided by the M-TOCA allows a simple, precise and accurate measurement for ambient samples having a low CC concentration.</p

Characteristics and major sources of carbonaceous aerosols in PM2.5 fromSanya, China

PM2.5 samples were collected in Sanya, China in summer and winter in 2012/2013. Organic carbon (OC), elemental carbon (EC), and non-polar organic compounds including n-alkanes (n-C14-n-C40) and polycyclic aromatic hydrocarbons (PAHs) were quantified. The concentrations of these carbonaceous matters were generally higher in winter than summer. The estimated secondary organic carbon (OCsec) accounted for 38% and 54% of the total organic carbon (TOC) in winter and summer, respectively. The higher value of OCsec in addition to the presences of photochemically-produced PAHs in summer supports that photochemical conversions of organics are much active at the higher air temperatures and with stronger intense solar radiation. Carbon preference index (CPI) and percent contribution of wax n-alkanes suggest that anthropogenic sources were more dominant than derivation from terrestrial plants in Sanya. Diagnostic ratios of atmospheric PAHs further indicate that there was a wide mix of pollution sources in winter while fossil fuel combustion was the most dominant in summer. Positive Matrix Factorization (PMF) analysis with 18 PAHs in the winter samples found that motor vehicle emissions and biomass burning were the two main pollution sources, contributing 37.5% and 24.6% of the total quantified PAHs, respectively.</p