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

Winter and Summer PM2.5 Chemical Compositions in Fourteen Chinese Cities

PM2.5 in 14 of China&#39;s large cities achieves high concentrations in both winter and summer with averages &gt; 100 mu g m(-3) being common occurrences. A grand average of 115 mu g m(-3) was found for all cities, with a minimum of 27 mu g m(-3) measured at Qingdao during summer and a maximum of 356 mu g m(-3) at Xi&#39;an during winter. Both primary and secondary PM2.5 are important contributors at all of the cities and during both winter and summer. While ammonium sulfate is a large contributor during both seasons, ammonium nitrate contributions are much larger during winter. Lead levels are still high in several cities, reaching an average of 1.68 mu g m(-3) in Xi&#39;an. High correlations of lead with arsenic and sulfate concentrations indicate that much of it derives from coal combustion, rather than leaded fuels, which were phased out by calendar year 2000. Although limited fugitive dust markers were available, scaling of iron by its ratios in source profiles shows similar to 20% of PM2.5 deriving from fugitive dust in most of the cities. Multipollutant control strategies will be needed that address incomplete combustion of coal and biomass, engine exhaust, and fugitive dust, as well as sulfur dioxide, oxides of nitrogen, and ammonia gaseous precursors for ammonium sulfate and ammonium nitrate.</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