This study investigated the air pollution characteristics of synoptic-scale circulation in the Beijing megacity, and provided quantitative evaluation of the impacts of circulation patterns on air quality during the 2008 Beijing Summer Olympics. Nine weather circulation types (CTs) were objectively identified over the North China region during 2000–2009, using obliquely rotated T-mode principal component analysis (PCA). The resulting CTs were examined in relation to the local meteorology, regional transport pathways, and air quality parameters, respectively. The FLEXPART-WRF model was used to calculate 48-h backward plume trajectories for each CT. Each CT was characterized with distinct local meteorology and air mass origin. CT 1 (high pressure to the west with a strong pressure gradient) was characterized by a northwestern air mass origin, with the smallest local and southeasterly air mass sources, and CT 6 (high pressure to the northwest) had air mass sources mostly from the north and east. On the contrary, CTs 5, 8, and 9 (weak pressure field, high pressure to the east, and low pressure to the northwest, respectively) were characterized by southern and southeastern trajectories, which indicated a greater influence of high pollutant emission sources. In turn, poor air quality in Beijing (high loadings of PM₁₀, BC, SO₂, NO₂, NO_x, O₃, AOD, and low visibility) was associated with these CTs. Good air quality in Beijing was associated with CTs 1 and 6. The average visibilities (with ±1σ) in Beijing for CTs 1 and 6 during 2000–2009 were 18.5 ± 8.3 km and 14.3 ± 8.5 km, respectively. In contrast, low visibility values of 6.0 ± 3.5 km, 6.6 ± 3.7 km, and 6.7 ± 3.6 km were found in CTs 5, 8, and 9, respectively. The mean concentrations of PM₁₀ for CTs 1, 6, 5, 8, and 9 during 2005–2009 were 90.3 ± 76.3 μg m⁻³, 111.7 ± 89.6 μg m⁻³, 173.4 ± 105.8 μg m⁻³, 158.4 ± 90.0 μg m⁻³, and 151.2 ± 93.1 μg m⁻³, respectively. Analysis of the relationship between circulation pattern and air quality during the emission control period suggests that CTs are the primary drivers of day-to-day variations in pollutant concentrations over Beijing and its vicinity. During the Olympics period, the frequency of CT 6 was twice that of the mean in August from 2000 to 2009. This CT had northerly transport pathways and favorable meteorological conditions (e.g. frequent precipitation) for clean air during the Olympics. Assuming that relationships between CTs and air quality parameters in the same season are fixed in different years, the relative contributions of synoptic circulation to decreases in PM₁₀, BC, SO₂, NO₂, NO_x, CO, and horizontal light extinction during the Olympics were estimated as 19 ± 14%, 18 ± 13%, 41 ± 36%, 12 ± 7%, 10 ± 5%, 19 ± 11%, and 54 ± 25%, respectively.

The "Blue Sky Project" was proposed in 1998 to investigate by how much emissions should be reduced to increase blue sky frequency in Beijing, which hosted the Summer Olympics in 2008. This paper focuses on the temporal variation of visibility and its dependence on meteorological conditions and suspended particles at Beijing using the hourly observed visibility data at Beijing Capital International Airport (BCIA) from 1999 to 2007. It has been found that about 47.8% (24.2%) of the hours in Beijing are "bad" ("good") hours with visibility below 10 km (equal or higher than 20 km) between 1999 and 2007. Due to the high Relative Humidity (RH), summer is the season with the lowest mean visibility in a year. Although PM₁₀ index was reported in a decreasing trend (Chan and Yao, 2008), the increase of RH has resulted in a decreasing trend of visibility over BCIA in the summer from 1999 to 2007. To ensure blue sky ("good" visibility) for Olympics 2008, daily mean PM₁₀ index should have been reduced from 81 to 44. This requires that not only vehicle emissions, but also other emissions should be limited. Observations verify that blue-sky-hour rate increased significantly after mean PM₁₀ index was reduced to 53 during Olympics 2008, however, the visibility of 2009 returned to the mean level from 1999 to 2007 during the period 8−24 August. RH (aerosol) contribute 24% (76%) of the improvement of visibility during August 2008.

Megacities are places with intensive human activity and energy consumption. To reduce air pollution, many megacities have relocated energy supplies and polluted industries to their outer regions. However, regional transport then becomes an important source of air pollution in megacities. To improve air quality before and during the 2008 Beijing Olympics, a wide range of control strategies were implemented, including the relocation of polluting industries. High sulfur dioxide (SO₂) concentrations were occasionally observed during this period. Potential sources from southern regions of Beijing were indicated by backward trajectories model and urban/rural stationary measurements, but direct evidence was lacking. Here we used a mobile laboratory to characterize the spatial distribution and regional transport of SO₂ to Beijing during the Campaign for Air Quality Research in Beijing and the Surrounding Region (CAREBEIJING)-2008. Among the five days chosen for the case studies during the Olympic air pollution control period, four had high SO₂ concentrations (6, 20 August and 3, 4 September 2008) while one had low SO₂ concentration (11 September 2008). The average values of SO₂ during the low SO₂ concentration day were 3.9 ppb, much lower than during the high concentration days (7.8 ppb). This result implied an impact by regional transport from outside Beijing. During these days, we captured transport events of SO₂ from areas south of Beijing, with a clear decrease in SO₂ concentrations southeast of the 6th to 4th Ring Roads around Beijing and along the 140 km highway from Tianjin to Beijing. The influx of SO₂ through the 4th to 6th Ring Roads ranged from 2.1 to 4.6 kg s⁻¹ on 4 September and 0.2 to 1.6 kg s⁻¹ on 20 August 2008. The differences of influx in days were due to the variations of emission changes, transport directions and dilutions. Locally emitted SO₂ from a source located along Jingshi Highway outside the southwest section of the 5th Ring Road of Beijing was identified using wind field data generated by the Weather Research and Forecasting model and the measured particle size distribution, with an estimated flux of 0.1 kg s⁻¹ to Beijing. Estimated uncertainties for SO₂ influx were approximately 31%.

The crystal structure of desheptapeptide (B24–B30) insulin (DHPI), a virtually inactive analog of insulin, was determined at 1.6 Å resolution. In the refined structure model, DHPI retains three α-helices (A1–A8, A12–A18, and B9–B19) as its structural framework, while great conformational changes occur in the N and C termini of B-chain. The β-turn, which lies in B20–B30 in insulin and insulin analogs with high potency, no longer exists in DHPI. Relative motion is observed among the three α-helices, each as a rigid functional group. In contrast, a region covering B5–B6 and A6–A11 exhibits a relatively stable conformation. We interpret our results as identifying: ( i ) the importance of β-turn in determining the receptor-binding potency of insulin and ( ii ) a leading role of Phe ^B24 in maintaining the β-turn structure.

The North China Plain (NCP) has been experiencing severe air pollution problems with rapid economic growth and urbanisation. Many field and model studies have examined the distribution of air pollutants in the NCP, but convincing results have not been achieved, mainly due to a lack of direct measurements of pollutants over large areas. Here, we employed a mobile laboratory to observe the main air pollutants in a large part of the NCP from 11 June to 15 July 2013. High median concentrations of sulfur dioxide (SO₂) (12 ppb), nitrogen oxides (NO_x) (NO + NO₂; 452 ppb), carbon monoxide (CO) (956 ppb), black carbon (BC; 5.5 µg m⁻³) and ultrafine particles (28 350 cm⁻³) were measured. Most of the high values, i.e. 95 percentile concentrations, were distributed near large cities, suggesting the influence of local emissions. In addition, we analysed the regional transport of SO₂ and CO, relatively long-lived pollutants, based on our mobile observations together with wind field and satellite data analyses. Our results suggested that, for border areas of the NCP, wind from outside this area would have a diluting effect on pollutants, while south winds would bring in pollutants that have accumulated during transport through other parts of the NCP. For the central NCP, the concentrations of pollutants were likely to remain at high levels, partly due to the influence of regional transport by prevalent south–north winds over the NCP and partly by local emissions.