Yujing Mu

Levels, sources and health risks of carbonyls and BTEX in the ambient air of Beijing, China.

The atmospheric concentrations of carbonyls and BTEX (benzene, toluene, ethylbenzene, m,p-xylene and o-xylene) were measured simultaneously at a same sampling site in Beijing from September 2008 to August 2010. The average concentrations of the total measured carbonyls during autumn, winter, spring, and summer were 37.7, 31.3, 39.7, 50.5 microg/m3, respectively, and maximal values for their diurnal variations usually happened at noontime. In contrast to carbonyls, the average concentrations of the total measured BTEX during the four seasons were 27.2, 31.9, 23.2, 19.1 microg/m3, respectively, and minimal values for their diurnal variations always occurred in the early afternoon. The average concentration for carbonyls increased about 24% from September 2008-August 2009 to September 2009-August 2010, for BTEX, increased about 15%. Integrated life time cancer risks for three carcinogens (benzene, formaldehyde and acetaldehyde) in Beijing exceeded the value of 1E-06, and the hazard quotient (HQ) of non-cancer risk of exposure to formaldehyde exceeded unity.

Atmospheric levels of BTEX compounds during the 2008 Olympic Games in the urban area of Beijing

The hourly concentrations of BTEX (Benzene, Toluene, Ethylbenzene, m,p-Xylene and o-Xylene) in the urban area of Beijing were measured during July-October 2008, covering the periods of the 2008 Olympic Games and Paralympic Games. The atmospheric BTEX were pre-concentrated on Tenax-TA tubes, and analyzed by GC-PID (Gas Chromatography with Photo Ionization Detector) after thermal desorption. During the games, the mean daytime concentrations of benzene, toluene, ethylbenzene, m,p-xylene and o-xylene were 2.37, 3.97, 1.92, 3.51 and 1.90 microg/m3, respectively, and were 52.8%, 63.9%, 56.4%, 56.8% and 46.9%, respectively lower than those after the games. The significantly positive correlation between BTEX and CO as well as the ratio of benzene/toluene suggested that the vehicle exhaust was the major source of BTEX during the whole investigated period. The extremely high ratios of ethylbenzene to m,p-xylene (E/X) were mainly observed at noontime in haze days, indicating that photochemical reactions were highly active under these typical days.

Preliminary report on methane emissions from the Three Gorges Reservoir in the summer drainage period

Recently reported summertime methane (CH4) emissions (6.7 +/- 13.3 mg CH4/(m2 x hr)) from newly created marshes in the drawdown area of the Three Gorges Reservoir (TGR), China have triggered broad concern in academic circles and among the public. The CH4 emissions from TGR water surfaces and drawdown areas were monitored from 3rd June to 16th October 2010 with floating and static chambers and gas chromatography. The average CH4 emission flux from permanently flooded areas in Zigui, Wushan and Yunyang Counties was (0.33 +/- 0.09) mg CH4/(m2 x hr). In half of these hottest months of the year, the wilderness, cropland and deforested drawdown sites were aerobic and located above water level, and the CH4 emissions were very small, ranging from a sink at 0.12 mg CH4/(m2 x hr) to a source at 0.08 mg CH4/(m2 x hr) except for one mud-covered site after flood. Mean CH4 emission in flooded drawdown sites was 0.34 mg CH4/(m2 x hr). The emissions from the rice paddy sites in the drawdown area were averaged at (4.86 +/- 2.31) mg CH4/(m2 x hr). Excepting the rice-paddy sites, these results show much lower emission levels than previously reported. Our results indicated considerable spatial and temporal variation in CH4 emissions from the TGR. Human activities and occasional events, such as flood, may also affect emission levels. Long-term CH4 measurements and modeling in a large region are necessary to accurately estimate greenhouse gas emissions from the TGR.

Nitrous oxide emissions from a maize field during two consecutive growing seasons in the North China Plain

Nitrous oxide (N2O) emissions from a maize field in the North China Plain (Wangdu County, Hebei Province, China) were investigated using static chambers during two consecutive maize growing seasons in the 2008 and 2009. The N2O pulse emissions occurred with duration of about 10 days after basal and additional fertilizer applications in the both years. The average N20 fluxes from the CK (control plot, without crop, fertilization and irrigation), NP (chemical N fertilizer), SN (wheat straw returning plus chemical N fertilizer), OM-1/2N (chicken manure plus half chemical N fertilizer) and OMN (chicken manure plus chemical N fertilizer) plots in 2008 were 8.51, 72.1, 76.6, 101, 107 ng N/(m2 x sec), respectively, and in 2009 were 33.7, 30.0 and 35.0 ng N/(m2 x sec) from CK, NP and SN plots, respectively. The emission factors of the applied fertilizer as N20-N (EFs) were 3.8% (2008) and 1.1% (2009) for the NP plot, 3.2% (2008) and 1.2% (2009) for the SN plot, and 2.8% and 2.2% in 2008 for the OM-1/2N and OMN plots, respectively. Hydromorphic properties of the investigated soil (with gley) are in favor of denitrification. The large differences of the soil temperature and water-filled pore space (WFPS) between the two maize seasons were suspected to be responsible for the significant yearly variations. Compared with the treatments of NP and SN, chicken manure coupled with compound fertilizer application significantly reduced fertilizer loss rate as N2O-N.

Photochemical production of carbonyl sulfide in precipitation

The selective catalytic reduction (SCR) of NOx with oxo-organic compounds (CH3OH, C2H5OH, CH3CHO, CH3COOH, etc) over Ag/Al2O3 in excess oxygen was studied. When using C2H5OH as a reductant, the 4 % Ag/Al2O3 gave the highest NOx conversion (the maximal value was up to 99 % and the average value was ca 90%) in a wide temperature range (300 similar to 610 degreesC). C2H5OH was more efficient for SCR of NOx than C3H6, CH3OH, or CH3COOH, while extremely similar NOx conversion was obtained when using CH3CHO as a reductant. In-situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) showed that the formation of enolic species over Ag/Al2O3 resulted in high efficiency of C2H5OH and CH3CHO for SCR of NOx. The presence of H2O enhanced the NOx reduction by C2H5OH at low temperature, while the influence of H2O on the NOx reduction was little at high temperature.

The pollution levels of BTEX and carbonyls under haze and non-haze days in Beijing, China

The North China Plain including Beijing is frequently suffering from serious haze days in recent years. To best recognize the influence of haze days on regional air quality, the pollution levels of deleterious gases of BTEX (benzene, toluene, ethylbenzene, m,p-xylene and o-xylene) and carbonyls (formaldehyde, acetaldehyde and acetone) under haze and non-haze days were contrastively investigated during the period of September 2008-August 2010 in Beijing. In comparison with non-haze days, remarkable enhancement of BTEX and the carbonyls under haze days in winter was found, with enhancement factors of 1.9-5.7 for BTEX and of 1.5-4.2 for the carbonyls. Whereas the enhancement factors for both BTEX (1.0-3.0) and the carbonyls (1.2-1.9) under haze days in summer were relatively small. The ratios of each BTEX to CO under both haze days and non-haze days exhibited a minimal value in the afternoon, whereas maximal values for the ratios of the carbonyls to CO were usually found in the afternoon. The ratios of each BTEX to CO were extremely greater under haze days than those under non-haze days in winter, but no evident difference was found in summer. The ratios of each carbonyl under both haze days and non-haze days in summer were at least a factor of 2 greater than those in winter and only enhancement of the ratios under haze days was found in winter. The remarkably higher ratios of ethylbenzene to m,p-xylene under haze days than non-haze days in both winter and summer revealed high reactivity of photochemical reactions initiated by OH radicals under haze days.

Ambient levels of atmospheric carbonyls in Beijing during the 2008 Olympic Games

The measurements of atmospheric carbonyls concentrations in Beijing were conducted from 12 July to 8 October, 2008, covering the periods of the 2008 Olympic Games and Paralympic Games. Six carbonyls, including formaldehyde, acetaldehyde, acetone, butyraldehyde, valeraldehyde, and hexaldehyde, were identified in all air samples. The total average concentrations of these carbonyls before, during, and after traffic restriction were (48.1 +/- 15.2), (36.6 +/- 14.5) and (23.4 +/- 12.3) microg/m3, respectively. Compared with the period after traffic restriction, the distinct high concentrations of the carbonyls before and during traffic restriction were primarily ascribed to the remarkable contribution of photochemical reactions. With respect to our previous investigation in the summer of 2005, the reductions of formaldehyde, acetaldehyde and acetone during traffic restriction period were about 64%, 47% and 27%, respectively, indicating that the air cleaning actions adopted by the Chinese government for the two games were efficient. The lowest levels of atmospheric carbonyls and the extremely high composition proportion of acetone after the traffic restriction were mainly attributed to the long-term effect of the control measures for the two games.

Direct and simultaneous determination of trace-level carbon tetrachloride, peroxyacetyl nitrate, and peroxypropionyl nitrate using gas chromatography-electron capture detection

Gas chromatography equipped with electron capture detector (GC-ECD) has been widely used for detecting atmospheric peroxyacetyl nitrate (PAN) and peroxypropionyl nitrate (PPN). However, to the best of our knowledge, only a few capillary columns have been adopted for separation to achieve the direct and simultaneous analysis of the two atmospheric pollutants. This paper demonstrates a novel method for directly and simultaneously measuring atmospheric carbon tetrachloride (CCl(4)), PAN, and PPN using GC-ECD with a DB-1 separation column. The responses of the GC-ECD to PAN, PPN, and CCl(4) were individually calibrated by using gas mixtures prepared via volatilization of synthesized solutions of PAN and PPN or high-purity CCl(4) reagent in a Teflon Bag. The concentrations of PAN and PPN in the synthesized solutions were quantified by ion chromatography (IC). Further calibration of the GC-ECD for PAN was conducted by in situ photochemical formation of gaseous PAN which was quantified by a NO(x) analyzer. The two calibration methods agreed well with each other, and the overall uncertainties for measuring atmospheric PAN were estimated to be ± 13% and ± 15% based on the calibrations of IC and NO(x), respectively. The detection limits (three times the signal to noise ratio) for PAN, PPN, and CCl(4) were estimated to be 22, 36, and 5 pptv (parts per trillion by volume), respectively. The atmospheric concentrations of these compounds were measured for several days in August in Beijing, and the values obtained in this study were found to be in good agreement with the data reported in the literature for Beijing using other GC-ECD methods.

NO and N2O emissions from agricultural fields in the North China Plain: Origination and mitigation

Agricultural soil has been recognized as a major source of atmospheric NO and N2O emissions which have important impacts on regional and global environments. Here we comparably investigated the effects of ammonium, nitrate fertilizers and nitrification inhibitor dicyandiamide (DCD) addition on NO and N2O emissions from the agricultural soil in the North China Plain (NCP). Compared with the ammonium fertilizer application, the reductions of NO emissions caused by nitrate fertilizer and DCD addition were 100% and 93%, and of N2O emissions were 54% and 74%, respectively. Remarkable reductions of NO and N2O emissions were also observed from five different agricultural soils in the NCP by replacing ammonium with nitrate fertilizer, indicating that nitrification is the predominant process for the emissions of NO and N2O from the soils in the vast area of NCP. NO emission peaks were found to be several days later than N2O peaks after the application of ammonium fertilizer and flooding irrigation, implying that most of NO initially produced via nitrification process might be fast reduced to N2O under the high soil moisture condition. Interestingly, the relative contribution of denitrification to N2O emission showed obviously time-dependent, e.g., evident N2O emission caused by the application of nitrate was only observed after the basal fertilization for the maize and the topdressing for the wheat. Replacing ammonium with nitrate fertilizer and mixing with the nitrification inhibitor are verified to be effective measures for mitigating NO and N2O emissions from arable soils in the NCP.

An improved GC-ECD method for measuring atmospheric N2O

Gas chromatography equipped with an electron capture detector (GC-ECD) has been widely used for measuring atmospheric N2O, but nonlinear response and the influence of atmospheric CO2 have been recognized as defects for quantification. An original GC-ECD method using N2 as carrier gas was improved by introducing a small flow rate of CO2 makeup gas into the ECD, which could well remedy the above defects. The N2O signal of the improved method was 4-fold higher than that of the original method and the relative standard deviation was reduced from > 1% to 0.31%. N2O concentrations with different CO2 concentrations (172.2 x 10(-6)-1722 x 10(-6) mol/mol) measured by the improved GC-ECD method were in line with the actual N2O concentrations. However, the N2O concentrations detected by the original method were largely biased with a variation range of -4.5%-7%. The N2O fluxes between an agricultural field and the atmosphere measured by the original method were greatly overestimated in comparison with those measured by the improved method. Good linear correlation (R2 = 0.9996) between the response of the improved ECD and N2O concentrations (93 x 10(-9)-1966 x 10(-9) mol/mol) indicated that atmospheric N2O could be accurately quantified via a single standard gas. Atmospheric N20 concentrations comparatively measured by the improved method and a high precision GC-ECD method were in good agreement.