We analyzed the measurements of ozone (O3) and its precursors made at rural/suburban sites downwind of four large Chinese cities - Beijing, Shanghai, Guangzhou and Lanzhou, to elucidate their pollution characteristics, regional transport, in situ production, and impacts of heterogeneous processes. The same measurement techniques and observation-based model were used to minimize uncertainties in comparison of the results due to difference in methodologies. All four cities suffered from serious O3 pollution but showed different precursor distributions. The model-calculated in situ O3 production rates were compared with the observed change rates to infer the relative contributions of on-site photochemistry and transport. At the rural site downwind of Beijing, export of the well-processed urban plumes contributed to the extremely high O3 levels (up to an hourly value of 286 ppbv), while the O3 pollution observed at suburban sites of Shanghai, Guangzhou and Lanzhou was dominated by intense in situ production. The O3 production was in a volatile organic compound (VOC)-limited regime in both Shanghai and Guangzhou, and a NOx-limited regime in Lanzhou. The key VOC precursors are aromatics and alkenes in Shanghai, and aromatics in Guangzhou. The potential impacts on O3 production of several heterogeneous processes, namely, hydrolysis of dinitrogen pentoxide (N2O5), uptake of hydro peroxy radical (HO2) on particles and surface reactions of NO2 forming nitrous acid (HONO), were assessed. The analyses indicate the varying and considerable impacts of these processes in different areas of China depending on the atmospheric abundances of aerosol and NOx, and suggest the urgent need to better understand these processes and represent them in photochemical models.

Abstract. Despite a large volume of research over a number of years, our understandings of the key precursors that control tropospheric ozone production and the impacts of heterogeneous processes remain incomplete. In this study, we analyze measurements of ozone and its precursors made at rural/suburban sites downwind of four large Chinese cities – Beijing, Shanghai, Guangzhou and Lanzhou. At each site the same measurement techniques were utilized and a photochemical box model based on the Master Chemical Mechanism (v3.2) was applied, to minimize uncertainties in comparison of the results due to differences in methodology. All four cities suffered from severe ozone pollution. At the rural site of Beijing, export of the well-processed urban plumes contributed to the extremely high ozone levels (up to an hourly value of 286 ppbv), while the pollution observed at the suburban sites of Shanghai, Guangzhou and Lanzhou was characterized by intense in-situ ozone production. The major anthropogenic hydrocarbons were alkenes and aromatics in Beijing and Shanghai, aromatics in Guangzhou, and alkenes in Lanzhou. The ozone production was found to be in a VOCs-limited regime in both Shanghai and Guangzhou, and a mixed regime in Lanzhou. In Shanghai, the ozone formation was most sensitive to aromatics and alkenes, while in Guangzhou aromatics were the predominant ozone precursors. In Lanzhou, either controlling NOx or reducing emissions of olefins from the petrochemical industry would mitigate the local ozone production. The potential impacts of several heterogeneous processes on the ozone formation were assessed. The hydrolysis of dinitrogen pentoxide (N2O5), uptake of the hydroperoxyl radical (HO2) on particles, and surface reactions of NO2 forming nitrous acid (HONO) present considerable sources of uncertainty in the current studies of ozone chemistry. Further efforts are urgently required to better understand these processes and refine atmospheric models.

We report a measurement of the branching fraction for ψ(3770)→γχc1 and search for the transition ψ(3770)→γχc2 based on 2.92 fb-1 of e+e- data accumulated at s=3.773 GeV with the BESIII detector at the BEPCII collider. We measure B(ψ(3770)→γχc1)=(2.48±0.15±0.23)×10-3, which is the most precise measurement to date. The upper limit on the branching fraction of ψ(3770)→γχc2 at a 90% confidence level is B(ψ(3770)→γχc2)<0.64×10-3. The corresponding partial widths are Γ(ψ(3770)→γχc1)=(67.5±4.1±6.7) keV and Γ(ψ(3770)→γχc2)<17.4 keV.

The process e+e−→ pp̄π0has been studied by analyzing data collected at (formula presented) GeV, at (formula presented) GeV, and during a ψ(3770) line shape scan with the BESIII detector at the BEPCII collider. The Born cross section of p̄pπ0in the vicinity of the ψ(3770) is measured, and the Born cross section of ψ(3770) → p̄pπ0is extracted considering interference between resonant and continuum production amplitudes. Two solutions with the same probability and a significance of 1.5 σ are found. The solutions for the Born cross section of ψ(3770) → p̄pπ0are 33.8 ± 1.8 ± 2.1 pb and (formula presented) pb (< 0.22 pb at a 90% confidence level). Using the estimated cross section and a constant decay amplitude approximation, the cross section σ(p̄p → ψ(3770)π0) is calculated for the kinematic situation of the planned P̄ANDA experiment. The maximum cross section corresponding to the two solutions is expected to be less than 0.79 nb at 90% confidence level and 122 ± 10 nb at a center-of-mass energy of 5.26 GeV.

From December 2011 to May 2014, about 5 fb-1 of data were taken with the BESIII detector at center-of-mass energies between 3.810 GeV and 4.600 GeV to study the charmonium-like states and higher excited charmonium states. The time-integrated luminosity of the collected data sample is measured to a precision of 1% by analyzing events produced by the large-angle Bhabha scattering process.

We study the decays of the charmonium resonances J/ψ and ψ(3686) to the final states Ξ-Ξ+, Σ(1385) Σ(1385)± based on a single baryon tag method using data samples of (223.7±1.4)×106 J/ψ and (106.4±0.9)×106 ψ(3686) events collected with the BESIII detector at the BEPCII collider. The decay ψ(3686)→Σ(1385) Σ(1385)± is observed for the first time, and the measurements of the other processes, including the branching fractions and angular distributions, are in good agreement with, and much more precise than, the previously published results. Additionally, the ratios B(ψ(3686)→Ξ-Ξ+)B(J/ψ→Ξ-Ξ+), B(ψ(3686)→Σ(1385)-Σ(1385)+)B(J/ψ→Σ(1385)-Σ(1385)+) and B(ψ(3686)→Σ(1385)+Σ(1385)-)B(J/ψ→Σ(1385)+Σ(1385)-) are determined.

We study D0D̅0 pairs produced in e+e− collisions at √ s = 3.773 GeVusing a data sample of 2.92 fb−1 collected with the BESIII detector. We measuredthe asymmetry ACPKπ of the branching fractions of D → K−π+ in CP-odd and CP-even eigenstates to be (12.7 ± 1.3 ± 0.7) × 10−2. ACPKπ can be used to extract the strong phase difference δKπ between the doubly Cabibbo-suppressed process D̅0 → K−π+ and the Cabibbo-favored process D0 → K−π+. Using world-average values of external parameters, we obtain cos δKπ = 1.02 ±0.11 ±0.06 ±0.01. Here, the first and second uncertainties are statistical and systematic, respectively, while the third uncertainty arises from the external parameters. This is the most precise measurement of δKπ to date.

Based on (106.41±0.86)×106 ψ(3686) events collected with the BESIII detector at the BEPCII collider, the branching fractions of ψ(3686)→π+π-J/ψ, J/ψ→e+e-, and J/ψ→μ+μ- are measured. We obtain B[ψ(3686)→π+π-J/ψ]=(34.98±0.02±0.45)%, B[J/ψ→e+e-]=(5.983±0.007±0.037)%, and B[J/ψ→μ+μ-]=(5.973±0.007±0.038)%. The measurement of B[ψ(3686)→π+π-J/ψ] confirms the CLEO-c measurement, and is apparently larger than the others. The measured J/ψ leptonic decay branching fractions agree with previous experiments within one standard deviation. These results lead to B[J/ψ→l+l-]=(5.978±0.005±0.040)% by averaging over the e+e- and μ+μ- channels and a ratio of B[J/ψ→e+e-]/B[J/ψ→μ+μ-]=1.0017±0.0017±0.0033, which tests e-μ universality at the four tenths of a percent level. All the measurements presented in this paper are the most precise in the world to date.

Using a sample of 1.3 × 10(9)  J/ψ events collected with the BESIII detector, we report the first observation of η(')→π(+)π(-)π(+)π(-) and η(')→π(+)π(-)π(0)π(0). The measured branching fractions are B(η(')→π(+)π(-)π(+)π(-)) = [8.53 ± 0.69(stat.) ± 0.64(syst.)]×10(-5) and B(η(')→π(+)π(-)π(0) π(0)) = [1.82 ± 0.35(stat.) ± 0.18(syst.)] × 10(-4), which are consistent with theoretical predictions based on a combination of chiral perturbation theory and vector-meson dominance.

Using 2.92 fb-1 of electron-positron annihilation data collected at √s = 3.773 GeV with the BESIII detector, we report the results of a search for the flavor-changing neutral current process D0 →γγ using a double-tag technique. We find no signal and set an upper limit at 90% confidence level for the branching fraction of B(D0 →γγ)< 3.8 × 10-6. We also investigate D0-meson decay into two neutral pions, obtaining a branching fraction of B(D0 →π0π0)= (8.24 ± 0.21(stat) ± 0.30(syst)) × 10-4, the most precise measurement to date and consistent with the current world average.