[Source Apportionment of Ambient VOCs in Qingdao Based on Photochemical Loss Correction].

Ozone was one of the major pollutants affecting the environmental air quality in China. The accurate apportionment of key sources and their contributions of ambient ozone and its precursor VOCs played an important role in the effective prevention and control of ozone pollution. Therefore, this study utilized the photochemical-age-based parameterization method to estimate the initial concentrations of ambient VOCs data collected from January 1 to February 28, 2021 in Jiaozhou, Qingdao and corrected the photochemical losses of ambient VOC species. The positive matrix factorization(PMF) and ozone formation potential(OFP) models were used to conduct source apportionment of ambient VOCs and their OFPs so as to provide data support for the prevention and control of ozone pollution in Qingdao. The results showed that the average values of ambient ρ(TVOCs) and OFP in Qingdao during the study period were 65.9 µg·m-3 and 176.7 µg·m-3, respectively. Propane had the highest concentration(12.4 µg·m-3) and percentage(18.9%), whereas m/p-xylene had the highest OFP(24.6 µg·m-3) and percentage(13.9%). The mean initial concentration of TVOCs during the study was 153.1 µg·m-3, and its photochemical loss rate reached 63.8%. Alkenes were the VOC species with the highest photochemical loss rate(92.1%), and the photochemical loss rate of isoprene reached 98.6%, which was substantially higher than that of other VOC species. According to the source apportionment results of initial concentrations(IC-PMF), liquefied petroleum gas(24.2%), solvent use(17.8%), natural gas and petrochemical-related enterprises(16.6%), gasoline volatilization(13.2%), combustion and gasoline vehicle emissions(12.2%), biogenic emissions(8.6%), and diesel vehicle emissions(7.4%) were the main contributing sources of the ambient VOCs in Jiaozhou. Compared with the apportioned results of IC-PMF, the contribution of biogenic emissions was underestimated by 38.9% in the apportioned results based on observed concentrations(OC-PMF), and the contribution of natural gas and petrochemical-related enterprises was underestimated by 28.5%, and the underestimations of their contributions were substantially higher than those of other sources. Compared with that before the Spring Festival, the contribution of gasoline volatilization to ambient VOCs increased markedly during the Spring Festival, whereas the contributions of solvent use, combustion, and gasoline vehicle emissions to ambient VOCs increased most significantly after the Spring Festival. The main contributing sources of ambient ozone during the study period were solvent use(31.3%), natural gas and petrochemical-related enterprises(16.1%), biogenic emissions(14.5%), and combustion and gasoline vehicle emissions(13.2%). The primary contributors of ambient ozone in different Spring Festival periods showed substantial differences. Before the Spring Festival, solvent use had the highest contribution(71.1 µg·m-3), and gasoline volatilization was the highest contributor during the Spring Festival(34.4 µg·m-3), whereas biogenic emissions after the Spring Festival were the highest contributor(39.1 µg·m-3).

[Chemical Characteristics and Source Apportionment for VOCs During the Ozone Pollution Episodes and Non-ozone Pollution Periods in Qingdao].

The ambient concentration of ozone is high in Qingdao, and ozone pollution episodes occur frequently in summer. The refined source apportionment of ambient volatile organic compounds (VOCs) and their ozone formation potential (OFP) during ozone pollution episodes and non-ozone pollution periods can play an important role in effectively reducing air ozone pollution in coastal cities and continuously improving ambient air quality. Therefore, this study applied the online VOCs monitoring data with hourly resolution in summer (from June to August) in 2020 in Qingdao to analyze the chemical characteristics of ambient VOCs during the ozone pollution episodes and non-ozone pollution periods and conducted the refined source apportionment of ambient VOCs and their OFP using a positive matrix factorization (PMF) model. The results showed that the average mass concentration of ambient VOCs in Qingdao in summer was 93.8 µg·m-3, and compared with that during the non-ozone pollution period, the mass concentration of ambient VOCs during the ozone pollution episodes increased by 49.3%, and the mass concentration of aromatic hydrocarbons increased by 59.7%. The total OFP of ambient VOCs in summer was 246.3 µg·m-3. Compared with that in the non-ozone pollution period, the total OFP of ambient VOCs in the ozone pollution episodes increased by 43.1%; that of alkanes increased the most, reaching 58.8%. M-ethyltoluene and 2,3-dimethylpentane were the species with the largest increase in OFP and its proportion during the ozone pollution episodes. The main contributors of ambient VOCs in Qingdao in summer were diesel vehicles (11.2%), solvent use (4.7%), liquefied petroleum gas and natural gas (LPG/NG) (27.5%), gasoline vehicles (8.9%), gasoline volatilization (26.6%), emissions of combustion- and petrochemical-related enterprises (16.4%), and plant emissions (4.8%). Compared with that in the non-ozone pollution period, the contribution concentration of LPG/NG in the ozone pollution episodes increased by 16.4 µg·m-3, which was the source category with the largest increase. The contribution concentration of plant emissions increased by 88.6% in the ozone pollution episodes, which was the source category with the highest increase rate. In addition, emissions from combustion- and petrochemical-related enterprises were the largest contributor to the OFP of ambient VOCs in summer in Qingdao, with its OFP and contribution proportion being 38.0 µg·m-3and 24.5%, respectively, followed by that of LPG/NG and gasoline volatilization. Compared with the non-ozone pollution period, the total contributions of LPG/NG, gasoline volatilization, and solvent use to the increase in OFP for ambient VOCs in the ozone pollution episodes were 74.1%, which were the main contribution source categories.

Short-term outcomes of near-infrared imaging using indocyanine green in laparoscopic lateral pelvic lymph node dissection for middle-lower rectal cancer: A propensity score-matched cohort analysis.

Laparoscopic lateral pelvic lymph node dissection (LPND) is limited by complex neurovascular bundles in the narrow pelvic sidewall and various post-operative complications. Indocyanine green (ICG) has been applied to increase the number of harvested lymph nodes and reduce the injury of irrelevant vessels in patients with rectal cancer. However, few studies on the recurrence rate of ICG fluorescence imaging-guided laparoscopic LPND were reported. This retrospective study enrolled 50 middle- low rectal cancer patients who were treated by LPND. After propensity score matching, 20 patients were matched in each of the indocyanine green (ICG) guided imaging group (ICG group) and non-ICG guided imaging group (non-ICG group). The average follow-up time was 13.5 months (12-15 months). Our results showed that the total number of harvested lymph nodes in the ICG group was significantly higher than that in the non-ICG group (P < 0.05), and intraoperative blood loss and post-operative hospital stay times in the ICG group were less than those in the non-ICG group (P < 0.05). After 12 months of follow-up, no residual lymph node and local tumor recurrence were found for patients in the ICG group. Four patients in the non-ICG group detected residual lymph nodes at the 3-month visit. Our findings highlighted the importance of ICG fluorescence-guided imaging in LPND because it has unique advantages in improving the number of lymph node dissections, surgical accuracy, and decreasing the residual lymph nodes and local tumor recurrence. In addition, ICG fluorescence guidance technology can effectively shorten the operation time, and it is simple to operate, which is worth popularizing.

[Characteristics of Ozone and Source Apportionment of the Precursor VOCs in Tianjin Suburbs in Summer].

From June to August 2018, a 1-hr resolution concentration dataset of ozone and its gaseous precursors (volatile organic compounds(VOCs) and NOx), and meteorological parameters were synchronously monitored by online instruments of the Nankai University Air Quality Research Supersite. The relationships and variation characteristics between ozone and its precursors were analyzed. According to the photochemical age, the initial concentrations of VOCs were calculated, and the photochemical loss of the concentration of VOCs during the daytime (06:00-24:00) was corrected. The initial and directly monitored concentrations of VOCs were incorporated into the PMF model for source apportionment. The results indicated that the mean concentration of O3 in Tianjin in summer was (41.3±25.7)×10-9, while that of VOCs was (13.9±12.3)×10-9. The average concentration of alkane (7.0±6.8)×10-9 was clearly higher than that of other VOC species. The species with high concentrations of alkanes were propane and ethane, accounting for 47% of the total alkane concentration. The average ozone formation potential (OFP) in summer was 52.1×10-9, and the OFP value of alkene was the highest and its contribution reached 57%. During the daytime, alkene loss accounted for 75% of the total VOC loss. The major sources of VOCs that were calculated based on the initial concentration data were the chemical industry and solvent usage (25%), automobile exhaust (22%), combustion source (19%), LPG/NG (19%), and gasoline volatilization (15%), respectively. Compared with the apportionment results based on directly monitored concentrations, the contribution of the chemical industry and solvent usage decreased by 4%, while automobile exhaust decreased by 5%. By combining the results of PMF apportionment and the OFP model to analyze the relative contributions of emission sources to ozone formation, and we found that the highest contribution source of ozone was the chemical industry and solvent usage (26%) in summer. Compared with the analysis results based on the directly monitored concentrations, the OFP values of the chemical industry and solvent usage decreased by 7%, while that of NG/LPG apparently decreased by 13%.

[Spatial Temporal Characteristics and Cluster Analysis of Chemical Components for Ambient PM2.5 in Wuhan].

The characteristics of chemical components of particulate matter are good indicators for analyzing sources and causes of pollution. The spatial and temporal distribution characteristics of particulate matter can reflect regional pollution problems in urban development, providing a basic dataset to support effective control of particulate matter sources. We collected PM2.5 and analyzed its concentration and chemical components at eight sites during different seasons. The results indicated that the average concentration of PM2.5 in Wuhan reached 70.7 µg·m-3. The concentration of PM2.5 in winter (103.1 µg·m-3) was significantly higher than that of other seasons, and the lowest concentration was in autumn (52.4 µg·m-3). The concentrations of PM2.5 in Donghu Gaoxin, Zhuankou New Area, and Qingshan Ganghua Station were significantly higher than those at the other sites. The main chemical components in PM2.5 were OC and SO42-, accounting for 15.4% and 14.2%, respectively. The OC concentration was the highest in winter, whereas SO42-concentration was the highest in summer. The average annual OC/EC ratio was up to 2.80, lower in winter and spring, and higher in summer and autumn. Material reconstruction showed that secondary particles and organic matter (OM) were major substances, accounting for 32.34% and 20.44% of PM2.5 mass, respectively. Coal combustion and vehicle exhaust might be the main contributors to ambient PM2.5. The highest fractions for OM were at the Wujiashan and Donghu Gaoxin sites, whereas the fraction of secondary particles was higher at each site, suggesting that secondary pollution had obvious regional characteristics in Wuhan. Cluster analysis based on the characteristics of chemical components showed that the eight sites were divided into three clusters:1 Hanyang Yuehu, Haze, Donghu Liyuan, and Huangpi sites, where the main characteristics were that the concentrations of components at each point were low; ② Zhuankou New Area and Qingshan Ganghua, which were characterized by higher nitrogen components; and ③ Donghu Gaoxin and Wujiashan, where not only industrial sources were heavily polluted in Wuhan, but also motor vehicles and dust pollution greatly contributed.

[Seasonal Variation of Carbon Fractions in PM2.5 in Heze].

PM2.5 samples were collected in Heze from August 2015 to April 2016. Eight carbon fractions were analyzed by a thermal/optical carbon analyzer, and organic carbon (OC) and elemental carbon (EC) analyses were obtained. The OC/EC ratio and the correlation between OC and EC were analyzed. Secondary organic carbon (SOC) mass concentration was estimated by the OC/EC ratio method; and eight carbon fractions were analyzed using a principal component analysis. The results showed that:① The annual average mass concentrations of OC and EC were 1.2-60.6 µg·m-3 and 0.6-24.8 µg·m-3, respectively; and the characterization of OC and EC percentages in PM2.5 during different seasons were similar with winter > spring > autumn > summer. ② The annual average OC/EC ratio was 2.6±1.0, and the correlations between OC and EC during spring, summer, autumn, and winter were 0.91, 0.56, 0.86, and 0.75, respectively, and the estimated mass concentration of SOC was (4.7±5.0) µg·m-3. ③ The characterization of eight carbon fractions percentages in PM2.5 in the different seasons demonstrated similar seasonal variations, with EC1 having the highest percentage and EC3 having the lowest percentage. The result of the principal component analysis showed that coal burning, motor vehicle emissions, and biomass burning were the major sources of carbon.

Characterization and source apportionment of size-segregated atmospheric particulate matter collected at ground level and from the urban canopy in Tianjin.

To investigate the size distributions of chemical compositions and sources of particulate matter (PM) at ground level and from the urban canopy, a study was conducted on a 255 m meteorological tower in Tianjin from December 2013 to January 2014. Thirteen sets of 8 size-segregated particles were collected with cascade impactor at 10 m and 220 m. Twelve components of particles, including water-soluble inorganic ions and carbonaceous species, were analyzed and used to apportion the sources of PM with positive matrix factorization. Our results indicated that the concentrations, size distributions of chemical compositions and sources of PM at the urban canopy were affected by regional transport due to a stable layer approximately 200 m and higher wind speed at 220 m. The concentrations of PM, Cl- and elemental carbon (EC) in fine particles at 10 m were higher than that at 220 m, while the reverse was true for NO3- and SO42-. The concentrations of Na+, Ca2+, Mg2+, Cl- and EC in coarse particles at 10 m were higher than that at 220 m. The size distributions of major primary species, such as Cl-, Na+, Ca2+, Mg2+ and EC, were similar at two different heights, indicating that there were common and dominant sources. The peaks of SO42-, NH4+, NO3- and organic carbon (OC), which were partly secondary generated species, shifted slightly to the smaller particles at 220 m, indicating that there was a different formation mechanism. Industrial pollution and coal combustion, re-suspended dust and marine salt, traffic emissions and transport, and secondary inorganic aerosols were the major sources of PM at both heights. With the increase in vertical height, the influence of traffic emissions, re-suspended dust and biomass burning on PM weakened, but the characteristics of regional transport from Hebei Province and Beijing gradually become obvious.