Long-term declining in carbon monoxide (CO) at a rural site of Beijing during 2006-2018 implies the improved combustion efficiency and effective emission control.

Carbon monoxide (CO) is primarily the result of incomplete combustion, which has important impacts on the atmospheric chemical cycle and climate. Improved quantitative characterization of long-term CO trends is important for both atmospheric modeling and the design and implementation of policies to efficiently control multiple pollutants. Due to the limitations of high time-resolution and high-quality long-term observational data, studies on long-term trends in the CO concentration in China are quite limited. In this study, the observational data of the concentration of CO in a rural site of Beijing during 2006-2018 was used to analyze the long-term trend in CO concentration in Beijing. The Theil-Sen method and the generalized additive model (GAM)-based method, were used to conduct the trend estimation analysis. We found that the concentration of CO at the Shangdianzi site showed a significant downward trend during 2006-2018, with a decline rate of 22.8 ± 5.1 ppbV per year. The declining trend in CO also showed phasic characteristics, with a fast decreasing rate during the period of 2006-2008, stable variations during the period of 2009-2013 and a continuous downward trend after 2013. The declining trend in the CO concentration in the south to west (S-W) sectors where the polluted air masses come from is more rapid than that in the sectors where the clean air masses come from. The declining trend in the CO concentration implies the improved combustion efficiency and the successful air pollution control policies in Beijing and the surrounding area.

[Characteristics of BTEX and Health Risk Assessment During Typical Pollution Episodes in Summer and Winter in Tianjin Urban Area].

Real-time BTEX(including benzene, toluene, ethylbenzene, m-, p-, and o-xylenes) were measured continuously in Tianjin urban site in July 2019 and January 2020 using a Syntech Spectras GC955 analyzer. The BTEX concentration levels, composition, and evolutionary mechanisms during typical pollution episodes were investigated. The potential sources of BTEX were analyzed qualitatively using the diagnostic ratios method. Finally, the BTEX health risk was evaluated by using the human exposure analysis and evaluation method according to US EPA. The averaged total mixing ratio of BTEX were 1.32×10-9 and 4.83×10-9 during ozone pollution and haze episodes, respectively. Benzene was the most abundant species, followed by toluene. The mixing ratio of BTEX was largely affected by short southwestern distance transportation in January, while local emissions in July. In addition, the BTEX mixing ratio depended on the influence of temperature and relative humidity(RH) in July, while the concentration was more sensitive to changes in RH when the temperature was low in January. Diagnostic ratios and source implications suggested that the BTEX was affected mainly by biomass/biofuel/coal burning during haze episodes. The traffic related emissions also had an impact except for the influence of biomass/biofuel/coal burning in July. The averaged hazard quotient(HQ) values were 0.072 and 0.29 during ozone pollution and haze episodes, respectively, which were in the upper safety range limit recommended by the US EPA. The carcinogenic risk posed by benzene in both cleaning and pollution processes was higher than the safety threshold set by the US EPA, which should be monitored carefully.

[Similarities and Differences of Valley Winds in the Beijing Plain and Yanqing Areas and Its Impact on Pollution].

Under certain terrain and weather conditions, mountain-valley circulation is one of the main meteorological factors affecting aerosol pollution in plain-mountain area. Based on environmental monitoring data and multi-source meteorological data for the Beijing-Tianjin-Hebei region between 2015 and 2019, the characteristics, similarities, and differences of mountain-valley winds in the Beijing Plain and Yanhuai Basin regions were compared. The results show that the mountain-valley winds recorded at the Beijing Observatory are from southwest to northeast compared to from the southeast to northeast at Yanqing station. With the aggravation of pollution levels, the mountain-valley wind intensity decreased by 17.7%-32.4%. When the wind speed at Beijing Observatory was 2-6 m·s-1, the maximum PM2.5 concentration in southeast was 83 µg·m-3, which was higher than in the southwest. When the wind speed at the Yanqing station was 2-6 m·s-1, the PM2.5 concentrations in SE-SSE area was 20-40 µg·m-3 higher than in other directions, and the concentrations in the valley winds were 10-12 µg·m-3 higher than the average value for the last five years. Taking the typical heavy pollution event on March 5-8, 2015, as an example, the influence of mountain-valley winds is mainly reflected in the high humidity and regional transmission of southeast winds during the valley wind stage. The PM2.5 concentrations at the Yanqing station increased by 100-130 µg·m-3 during the valley wind stage on March 6 and 7, 2015. The inversion temperature developed to 1000 m during the mountain wind stage, the local dew point at the Beijing Observatory and the Yanqing station rose by approximately 18℃. The peak dew point at the Yanqing station occurring 2 hours after the Beijing Observatory, and the concentrations of PM2.5 rose slightly under high humidity conditions. Meanwhile, the thermal gradient between the 400-m-high Yanqing Station and Yudu Mountain gradually decreased, and the mountain-valley wind decreased by 8% and 6%, respectively. The weakening of local circulation may be related to the bidirectional feedback mechanism of the boundary layer and high concentrations of aerosols.

[Application of ARIMA Model for Mid- and Long-term Forecasting of Ozone Concentration].

Ozone pollution has recently become a severe air quality issue in the Beijing-Tianjin-Hebei region. Due to the lack of a precursor emission inventory and complexity of physical and chemical mechanism of ozone generation, numerical modeling still exhibits significant deviations in ozone forecasting. Owing to its simplicity and low calculation costs, the time series analysis model can be effectively applied for ozone pollution forecasting. We conducted a time series analysis of ozone concentration at Shangdianzi, Baoding, and Tianjin sites. Both seasonal and dynamic ARIMA models were established to perform mid- and long-term ozone forecasting. The correlation coefficient R between the predicted and observed value can reach 0.951, and the RMSE is only 10.2 µg·m-3 for the monthly average ozone prediction by the seasonal ARIMA model. The correlation coefficient R between the predicted and observed value increased from 0.296-0.455 to 0.670-0.748, and RMSE was effectively reduced for the 8-hour ozone average predicted by the dynamic ARIMA model.

Regional transport and urban emissions are important ammonia contributors in Beijing, China.

Measuring ammonia (NH3) is important for understanding the role of NH3 in secondary aerosol formation and the atmospheric deposition of reactive N. In this study, NH3 was measured in an urban area, a background region, and a tunnel in Beijing. The average NH3 concentrations between September 2017 and August 2018 were 24.8 ± 14.8 ppb and 11.6 ± 10.3 ppb in the urban area and background region, respectively. Higher NH3 concentrations at both the urban and background sites, relative to some earlier measurements indicated a likely increase in the NH3 concentrations in these regions. The urban NH3 level in Beijing was much higher than that typically observed at urban and industrial sites in other domestic and foreign cities, suggesting that the Beijing urban area was affected by greater NH3 emissions than other regions. Based on the relationship among NH3, wind direction, and wind speed, the urban area was affected by both local emissions and air transported from North China Plain (NCP). Potential source contribution function analyses suggested that regional transport from the NCP could greatly affect local concentrations of NH3 in both urban and background areas in spring and autumn; however, in addition to the NCP, urban emissions could also affect NH3 levels in the background region in summer and winter. The average NH3 concentration at the Fenshuiling Tunnel was 8.5 ± 7.7 ppb from December 2017 to February 2018. The NH3:CO emission ratio measured in the tunnel test was 0.022 ± 0.038 ppb/ppb, which was lower than values in the USA and South Korea. The contribution of traffic to NH3 in Beijing did not agree well with the available emission inventories, suggesting that vehicular emissions were underestimated and further evaluation is necessary.

[Characteristics of VOCs and Their Roles in Ozone Formation at a Regional Background Site in Beijing, China].

As important precursors of near-surface ozone, secondary organic aerosols (SOAs), and volatile organic compounds (VOCs) play an important role in photochemical reactions and fine particle formation. In this study, real-time VOCs were measured continuously by Syntech Spectras GC955 analyzers at the regional background site of the North China Plain from September 1 to 27, 2017. The VOC concentration levels, compositions, spatiotemporal variations, and the ozone formation potential during the observation period were investigated. The potential sources of initial VOCs indicated from the diagnostic ratios were further studied. The averaged total mixing ratio of VOCs was 12.53×10-9. Among all measured VOC species, alkanes were the most abundant species, which accounted for 65.3% of the total concentrations, followed by alkenes (26.7%) and aromatics (6.5%). In addition, the total OH radical loss rate of VOCs (L·OH) was 5.2 s-1. In particular, the contribution of C4-C5 alkenes to L·OH was as high as 61%, followed by C2-C3 alkenes, with a 12.8% contribution of L·OH. The average ozone formation potential of VOCs was 36.5×10-9. Among all the measured VOC species, alkenes were the most abundant species, which accounted for 71.2%. Among alkenes, the contribution of C4-C5 alkenes was the most prominent. Although the concentration of alkanes in Shangdianzi was much higher than other VOC species, the ozone formation potential was lower. Diagnostic ratios and source implications suggested that Shangdianzi was affected mainly by biomass/biofuel/coal burning, with substantially elevated benzene levels during the observation period, whereas a slight influence of traffic-related emissions was observed.

Characteristics and source implications of aromatic hydrocarbons at urban and background areas in Beijing, China.

The characteristics of benzene, toluene, ethylbenzene, and xylene (BTEX) concentrations, their temporal and spatial variations, and their source origins from September-December 2017 at an urban and a background site in Beijing, China were investigated. The averaged (±σ) total mixing ratios of benzene, toluene, ethylbenzene, m, p-xylenes, and o-xylene were 0.40 ± 0.39 ppbv, 0.31 ± 0.34 ppbv, 0.08 ± 0.07 ppbv, 0.08 ± 0.08 ppbv, and 0.05 ± 0.05 ppbv at the SDZ site, which were 63%, 79%, 83%, 85%, and 89% lower than those at the Chinese Academy of Meteorological Sciences site (CMA). It is worth noting that the average mixing ratios of BTEX at SDZ and CMA were 0.86 ± 1.03 ppbv and 3.38 ± 2.80 ppbv during the heating period (HP), which were 2.3% and 21.9% lower than those before the HP, a decrease that was mainly related to the frequent occurrence of strong northerly and northwesterly winds and low relative humidity (RH) during the HP. Obvious differences were also observed between the BTEX composition proportions at the SDZ and CMA sites. On average, benzene comprised 44% of the total BTEX at SDZ, whereas toluene was the largest contributor to the total BTEX at CMA, accounting for 37%. In addition, the contributions of C8 aromatics (the sum of ethylbenzene, m, p-xylenes, and o-xylene) at CMA (36%) were also higher than those at SDZ (21%), reflecting the different emission sources of the two sites. In addition, the BTEX species showed similar and pronounced diurnal profiles at SDZ and CMA, all characterized by much higher values at night than during the day. Diagnostic ratios and source implications suggested that SDZ was affected mainly by biomass/biofuel/coal burning, with substantially elevated benzene levels during the winter HP, whereas CMA was affected both by traffic-related emissions and biomass/biofuel/coal burning emissions. These findings suggest the necessity of regionally-tailored control strategies both to reduce BTEX levels and to mitigate their environmental impact. Further analysis of the backward trajectories revealed that the BTEX compounds varied greatly in terms of air mass origins, but generally exhibited high values for slow air masses passing over areas south of Beijing, with dominant contributions from benzene, toluene, and m, p-xylenes.

[Using Multiple Linear Regression Method to Evaluate the Impact of Meteorological Conditions and Control Measures on Air Quality in Beijing During APEC 2014].

Meteorological conditions have important impact on the diffusion and transport of air pollutants, thus separating and quantifying the impact of meteorological factors is a prerequisite for evaluation of air pollution control measures. Using observation data on SO2, NO, NO2, NOx, CO, PM2.5, PM1, and PM10 as well as meteorological factors at the Chaoyang site, an urban site in Beijing, we evaluated the impact of meteorological conditions and control measures on air quality in Beijing during APEC 2014 (from 15 October to 30 November, 2014) by the multiple linear regression method. The simulation performance of a multivariate linear regression model based on the parameters of meteorological factors for predicting pollutant concentration assuming constant emission conditions were ideal, produced a range of determination coefficient (R2) of 0.494-0.783. Our results suggested that air pollution control measures reduced the concentration of SO2, NO, NO2, NOx, CO, PM2.5, PM1, and PM10 by 48.3%, 53.5%, 18.7%, 40.6%, 3.6%, 34.8%, 28.8%, and 40.6%, while meteorological conditions reduced the concentration of SO2, NO, NO2, NOx, CO, PM2.5, PM1, and PM10 by 1.7%, -2.8%, 18.7%, 4.5%, 18.6%, 27.5%, 30.6%, and 35.6%. The combination of meteorological factors and control measures has significantly improved the air quality in Beijing during the APEC period. Control measures played a leading role in the reduction of SO2 and nitrogen oxides, and meteorological factors played a leading role in the reduction of CO. Meteorological factors and control measures made roughly equal contributions to the reduction of particulate matter. We also used the relative weight method to study the contribution of meteorological factors to the pollutant concentration. The results showed that the decisive meteorological factors on the concentrations of different pollutants were different.

18F-labeled pyrazolo[1,5-a]pyrimidine derivatives: synthesis from 2,4-dinitrobenzamide and tosylate precursors and comparative biological evaluation for tumor imaging with positron emission tomography.

We previously reported 18F-labeled pyrazolo[1,5-a]pyrimidine derivatives: 7-(2-[18F]fluoroethylamino)-5-methylpyrazolo[1,5-a]pyrimidine-3-carbonitrile ([18F]1) and N-(2-(3-cyano-5-methylpyrazolo[1,5-a]pyrimidin-7-ylamino)ethyl)-2-[18F]fluoro-4-nitro- benzamide ([18F]2). Preliminary biodistribution experiments of both compounds showed s slow clearance rate from excretory tissues which warranted further investigation for tumor imaging with PET. Here we modified [18F]1 and [18F]2 by introducing polar groups such as ester, hydroxyl and carboxyl and developed three additional 18F-18 labeled pyrazolo[1,5-a] pyrimidine derivatives: (3-Cyano-7-(2-[18F]fluoroethylamino)pyrazolo[1,5-a]-pyrimidin-5- yl)methyl acetate ([18F]3), 7-(2-[18F]fluoroethylamino)-5-(hydroxymethyl)pyrazolo[1,5-a]- pyrimidine-3-carbonitrile ([18F]4) and (S)-6-(3-cyano-5-methylpyrazolo[1,5-a]pyrimidin-7-ylamino)-2-(2-[18F]fluoro-4-nitrobenzamido)hexanoic acid ([18F]5). The radiolabeled probes were synthesized by nucleophilic substitution of the corresponding tosylate and nitro precursors with 18F-fluoride. In Vitro studies showed higher uptake of [18F]3 and [18F]4 than that of [18F]5 by S180 tumor cells. In Vivo biodistribution studies in mice bearing S180 tumors showed that the uptake of both [18F]3 and [18F]4 in tumors displayed an increasing trend while the uptake of [18F]5 in tumor decreased through the course of the 120 min study. This significant difference in tumor uptake was also found between [18F]1 and [18F]2. Thus, we compared the biological behavior of the five tracers and reported the tumor uptake kinetic differences between 2-[18F]fluoroethylamino- and 2-[18F]fluoro-4-nitro- benzamidopyrazolo[1,5-a] pyrimidine derivatives.