[Distribution Characteristics and Source Analysis of Carbonaceous Aerosols Before and After the Spring Festival in the Guanzhong Plain].

The spatio-temporal variation characteristics and potential sources of carbonaceous aerosols in the Guanzhong Plain during the Spring Festival in 2023 were analyzed using inverse distance weighting spatial interpolation （IDW）, secondary organic carbon （SOC） estimation, and potential source contribution factor analysis （PSCF）, with the OC and EC in the PM2.5 of five cities： Xi'an, Baoji, Xianyang, Weinan, and Tongchuan as the research objects. The results showed that in terms of time distribution, ρ（OC） was as follows： after the Spring Festival [（18.6 ±11.0） µg·m-3] > during the Spring Festival [（16.2 ±15.1） µg·m-3] > before the Spring Festival [（10.0 ±8.3） µg·m-3], and ρ（EC） was as follows： after the Spring Festival [（2.2 ±1.2） µg·m-3] > during the Spring Festival [（1.7 ±1.5） µg·m-3] > before the Spring Festival [（1.4 ±1.1） µg·m-3], which indicated that OC and EC concentrations were the most severe after the Spring Festival. In terms of spatial distribution, ρ（OC） was as follows： Xianyang [（21.4 ±17.3） µg·m-3] > Baoji [（15.8 ±12.8） µg·m-3] > Xi'an [（13.6 ±11.3） µg·m-3] > Weinan [（11.6 ±9.1） µg·m-3] > Tongchuan [（10.0 ±8.3） µg·m-3], and ρ（EC） was as follows： Xianyang [（2.1 ±1.4） µg·m-3] > Weinan [（1.8 ±1.4） µg·m-3] > Xi'an [（1.8 ±1.2） µg·m-3] > Tongchuan [（1.6 ±1.4） µg·m-3] > Baoji [（1.2 ±0.9） µg·m-3]. Overall, Xianyang had the most severe PM2.5 and carbon aerosol pollution, whereas Tongchuan had the least pollution. IDW results showed that the high-value center of OC and EC concentration [ρ（OC） > 27.3 µg·m-3, ρ（EC） > 2.9 µg·m-3] was in the middle of the plain, the low-value center of OC and EC concentration [ρ（OC） <7.0 µg·m-3, ρ（EC） < 1.0 µg·m-3] was in the northern plain, and the distribution of OC was higher in the west and lower in the east, whereas the distribution of EC was higher in the east and lower in the west. The proportion of SOC in OC was as follows： after the Spring Festival （51.7%） > during the Spring Festival （41.1%） > before the Spring Festival （36.8%）. The SOC/OC values of each city and the contribution rate of SOC of each city to the Guanzhong Plain indicated that Tongchuan, Baoji, and Xianyang were greatly affected by the secondary conversion of organic carbon. The correlation of OC and EC before, during, and after the Spring Festival （r = 0.85, r = 0.98, and r = 0.94, respectively） indicated a high degree of homology between them. Carbonaceous aerosols had a certain correlation with humidity and wind speed before and during the Spring Festival but had a weak correlation with meteorological factors after the Spring Festival. Carbonaceous aerosols generally were strongly correlated with CO and NO2, and the correlation was strongest after the Spring Festival, whereas the correlation with SO2 was strongest during the Spring Festival. The potential source areas of carbonaceous aerosols in the five cities were mainly concentrated in the local and surrounding areas of southern Gansu, northern Shaanxi, and southern Shaanxi. They were also affected by long-distance transportation from the northwest before the Spring Festival.

[Study on pollution characteristics of carbonaceous aerosols in Xi'an City during the spring festival].

The samples of PM2.5 with 8 times periods were collected using Automated Cartridge Collection Unit (ACCU) of Rupprecht& Patashnick (R&P)Corporation, and monitored by R&P1400a instrument of TEOM series online during 2011 Spring Festival in Xi'an city. The organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC) and water-insoluble organic carbon (WIOC) contents of 3 h integrated PM2.5 were analyzed to evaluate the influence of firework display on the carbonaceous components in urban air. The mass concentration of PM2.5 was found increased significantly from 00:00 A. M. to 02:59 A. M. at the Chinese Lunar New Year's Eve than the non-firework periods, reaching 1514.8 microg.m-3 at 01:00 A. M. The mass concentrations of OC, EC, WSOC, and WIOC during the same time period were 123.3 microg.m-3, 18.6 microg.m-3, 66.7 microg.m-3, and 56.6 microg.m-3, about 1.7, 1.2, 1.4, and 2.2 times higher than the average in normal days, respectively. Correlation analysis among WSOC, OC, and EC contents in PM25 showed that firework emission was an obvious source of carbonaceous aerosol in the Spring Festival vacation. However, it only contributes to 9. 4% for aerosol in fireworks emission.

[Pollution characterization and source apportionment of polybrominated diphenyl ethers in autumn air of Xi'an].

Air samples in gas and particle phases were collected using a high volume active sampler from August to October in 2008 at Xi'an for evaluating the pollution level of polybrominated diphenyl ethers (PBDEs). Lower brominated PBDEs and BDE-209 were analyzed via GC-MS and GC/ECD, respectively. The total concentrations (gas plus particle phases) of 12 PBDEs were ranged from 37.43 to 620.30 pg/m3, with an average of 216.28 pg/m3, while tri- to hexa-brominated congeners (Sigma11 PBDEs) ranged from 16.32 to 86. 49 pg/m3, BDE-209 ranged from 16. 34 to 576.01 pg/m3. Tri- to tetra-brominated congeners existed mainly in gas phase, tetra- to hexa-brominated congeners were predominated in particle phase, and BDE-209 was detected only in particle phase. The proportion of PBDEs in particle phase increased with bromine number. Gas-particle partition coefficient of PBDEs was well correlated with sub-cooled liquid vapor pressure, and the partitioning of PBDEs between gas and particle phases were close to equilibrium. Correlation analysis indicated that all the PBDEs have good coefficients except BDE-85. Source analysis indicated that PBDEs in the atmosphere of Xi'an were mainly from the Penta-BDE and Deca-BDE contamination.

[Pollution characterizations and source apportionment of polycyclic aromatic hydrocarbons in air during domestic heating season of Xi'an].

TSP samples and gas phase air samples were collected by an improved high volume active air sampler during domestic heating season in Xi'an, and the concentrations of polycyclic aromatic hydrocarbons (PAHs) were analyzed via GC-MS. The results showed that average concentrations of sigma 16 PAHs in TSP and gas phase were (108.15 +/- 41.44) ng/m3, (260.14 +/- 99.84) ng/m3, respectively. Two and three ring PAHs dominated in the gas phase, while more than four ring PAHs were mainly adsorbed on the particle phase. Good correlation was found between gas-particle partition coefficient and the respective sub-cooled vapor pressures of PAHs. A significant correlation was also found between partition coefficient and temperature, and the regression equation was put forward by stepwise linear regression method. Ratio analysis illustrated that coal burning and vehicle exhaust were the main source of PAHs in Xi' an. Contribution of each source was calculated by factor analysis and multiple linear regression. Partial correlation analysis was applied to study the relationship between air pollution indexes and some representative PAHs of individual factors, which indicated some PAH had same source to SO2 and NO2.