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 μg/m 3,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 μg/m 3,respectively,andminimal 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.
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 GCECD method using N 2 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 （172.2×10-6-1722×10-6mol/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 （93×10-9-1966×10-9mol/mol） indicated that atmospheric N2O could be accurately quantified via a single standard gas.Atmospheric N2O concentrations comparatively measured by the improved method and a high precision GC-ECD method were in good agreement.
Nitrous oxide （N 2 O） 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 N 2 O pulse emissions occurred with duration of about 10 days after basal and additional fertilizer applications in the both years.The average N 2 O 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/（m 2 ·sec）,respectively,and in 2009 were 33.7,30.0 and 35.0 ng N/（m 2 ·sec） from CK,NP and SN plots,respectively.The emission factors of the applied fertilizer as N 2 O-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 N 2 O-N.
Atmospheric peroxyacetyl nitrate （PAN）, peroxypropionyl nitrate （PPN）, and carbon tetrachloride （CCl4） were measured from September 2010 to August 2011 in Beijing. PAN exhibited low values from mid-autumn to early spring （October to March） with monthly average concentrations ranging from 0.28 to 0.73 ppbV, and increased from early spring to summer （March to August）, ranging from 1.37-3.79 ppbV. The monthly variation of PPN was similar to PAN, with low values （below detection limit to 0.18 ppbV） from mid-autumn to early spring, and a monthly maximum in September （1.14 ppbV）. The monthly variation of CCl4 was tightly related to the variation of temperature, exhibiting a minimum in winter （69.3 pptV） and a maximum of 180.6 pptV in summer. Due to weak solar intensity and short duration, PAN and O3 showed no distinct diurnal patterns from morning to night during winter, whereas for other seasons, they both exhibited maximal values in the late afternoon （ca. 15：00 to 16：00 local time） and minimal values during early morning and midnight. Good linear correlations between PAN and PPN were found in autumn （R = 0.91）, spring （R = 0.94）, and summer （R = 0.81）, with slopes of 0.130, 0.222, and 0.133, respectively, suggesting that anthropogenic hydrocarbons dominated the photochemical formation of PANs in Beijing. Positive correlation between PAN and O3 in summer with the low slopes （AO3/APAN） ranging from 9.92 to 18.0 indicated serious air pollution in Beijing, and strong negative correlation in winter reflected strong O3 consumption by NO titration and less thermal decompositin of PAN.
Gen ZhangYujing MuJunfeng LiuChenglong ZhangYuanyuan ZhangYujie ZhangHongxing Zhang
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） μg/m^3, 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.
