ALBERT

Description: This study investigates the impact of the aerosol hygroscopic growth effect on haze events in Xingtai, a heavily polluted city in the central part of the North China Plain (NCP), using a large array of instruments measuring aerosol optical, physical, and chemical properties. Key instruments used and measurements made include the Raman lidar for atmospheric water vapor content and aerosol optical profiles, the PC-3016A GrayWolf six-channel handheld particle and mass meter for atmospheric total particulate matter (PM) that has diameters less than 1 and 2.5 µm (PM1 and PM2.5, respectively), the aerosol chemical speciation monitor (ACSM) for chemical components in PM1, and the hygroscopic tandem differential mobility analyzer (H-TDMA) for aerosol hygroscopicity. The changes in PM1 and PM2.5 agreed well with that of the water vapor content due to the aerosol hygroscopic growth effect. Two cases were selected to further analyze the effects of aerosol hygroscopic growth on haze events. The lidar-estimated hygroscopic enhancement factor for the aerosol backscattering coefficient during a relatively clean period (Case I) was lower than that during a pollution event (Case II) with similar relative humidity (RH) levels of 80 %–91 %. The Kasten model was used to fit the aerosol optical hygroscopic growth factor (GF) whose parameter b differed considerably between the two cases, i.e., 0.1000 (Case I) versus 0.9346 (Case II). The aerosol acidity value calculated from ACSM data for Case I (1.35) was less than that for Case II (1.50) due to different amounts of inorganics such as NH4NO3, NH4HSO4, and (NH4)2SO4. Model results based on H-TDMA data showed that aerosol hygroscopic growth factors in each size category (40, 80, 110, 150, and 200 nm) at different RH levels (80 %–91 %) for Case I were lower than those for Case II. For similar ambient RH levels, the high content of nitrate facilitates the hygroscopic growth of aerosols, which may be a major factor contributing to heavy haze episodes in Xingtai.

Description: Magnetic reconnection processes in the near-Earth magnetotail can be highly three-dimensional (3-D) in geometry and dynamics, even though the magnetotail configuration itself is nearly two-dimensional due to the symmetry in the dusk–dawn direction. Such reconnection processes can be induced by the 3-D dynamics of nonlinear ballooning instability. In this work, we explore the global 3-D geometry of the reconnection process induced by ballooning instability in the near-Earth magnetotail by examining the distribution of quasi-separatrix layers associated with plasmoid formation in the entire 3-D domain of magnetotail configuration, using an algorithm previously developed in the context of solar physics. The 3-D distribution of quasi-separatrix layers (QSLs) as well as their evolution directly follow the plasmoid formation during the nonlinear development of ballooning instability in both time and space. Such a close correlation demonstrates a strong coupling between the ballooning and the corresponding reconnection processes. It further confirms the intrinsic 3-D nature of the ballooning-induced plasmoid formation and reconnection processes, in both geometry and dynamics. In addition, the reconstruction of the 3-D QSL geometry may provide an alternative means of identifying the location and timing of 3-D reconnection sites in the magnetotail from both numerical simulations and satellite observations.

Description: Magnetic reconnection processes in the near-Earth magnetotail can be highly 3-dimensional (3D) in geometry and dynamics, even though the magnetotail configuration itself is nearly two dimensional due to the symmetry in the dusk-dawn direction. Such reconnection processes can be induced by the 3D dynamics of nonlinear ballooning instability. In this work, we explore the global 3D geometry of the reconnection process induced by ballooning instability in the near-Earth magnetotail by examining the distribution of quasi-separatrix layers associated with plasmoid formation in the entire 3D domain of magnetotail configuration, using an algorithm previously developed in context of solar physics. The 3D distribution of quasi-separatrix layers (QSLs) as well as their evolution directly follows the plasmoid formation during the nonlinear development of ballooning instability in both time and space. Such a close correlation demonstrates a strong coupling between the ballooning and the corresponding reconnection processes. It further confirms the intrinsic 3D nature of the ballooning-induced plasmoid formation and reconnection processes, in both geometry and dynamics. In addition, the reconstruction of the 3D QSL geometry may provide an alternative means for identifying the location and timing of 3D reconnection sites in magnetotail from both numerical simulations and satellite observations.

Description: A small and portable incoherent broadband cavity-enhanced absorption spectrometer (IBBCEAS) for NO3 and N2O5 measurement has been developed. The instrument features a mechanically aligned non-adjustable optical mounting system, and the novel design of the optical mounting system enables a fast setup and stable operation in field applications. To remove the influence of the strong nonlinear absorption by water vapour, a dynamic reference spectrum through NO titration is used for the spectrum analysis. The wall loss effects of the sample system were extensively studied, and the total transmission efficiencies were determined to be 85 and 55 % for N2O5 and NO3, respectively, for our experimental setup. The limit of detection (LOD) was estimated to be 2.4 pptv (1σ) and 2.7 pptv (1σ) at 1 s intervals for NO3 and N2O5, respectively. The associated uncertainty of the field measurement was estimated to be 19 % for NO3 and 22–36 % for N2O5 measurements from the uncertainties of transmission efficiency, absorption cross section, effective cavity length, and mirror reflectivity. The instrument was successfully deployed in two comprehensive field campaigns conducted in the winter and summer of 2016 in Beijing. Up to 1.0 ppb NO3+N2O5 was observed with the presence of high aerosol loadings, which indicates an active night-time chemistry in Beijing.

Description: The hygroscopic growth of aerosol particles is a key factor of air pollution because it can significantly reduce visibility. In order to better understand the impact of the hygroscopic growth effect on haze events and contributing factors, we made use of rich measurements during an intensive field campaign conducted in Xingtai, Hebei province of China that has suffered from the most serious pollution in the Northern China Plain. Key measurements are from Raman lidar and ground-based instruments such as a GrayWolf 6-channel handheld particle/mass meter for atmospheric particulate matter that have diameters less than 1μm and 2.5μm (PM1 and PM2.5, respectively), aerosol chemical speciation monitor (ACSM), and a hygroscopic tandem differential mobility analyzer (H-TDMA). The evolution of PM1 and PM2.5 agreed well with that of the water vapor content due to the aerosol hygroscopic growth effect. Two cases were selected to further analyze the effects of aerosol particle hygroscopic growth on haze events. The lidar-estimated aerosol hygroscopic enhancement factor during a pollution event (Case II) was greater than that during a relatively clean period (Case I) with similar relative humidity (RH): 80–91%. The hygroscopic growth was fitted by the Kasten model whose parameter b differ considerably: 0.9346 vs. 0.1000 for cases II and I respectively. The aerosol acidity value of Case II (1.50) was greater than that of Case I (1.35) due to different amounts of inorganics such as NH4NO3, NH4HSO4, and (NH4)2SO4, consistent with the difference in the aerosol hygroscopicity parameter κ calculated from the chemical species of PM1 obtained by the ACSM. Data from the H-TDMA showed that all of the aerosol particle size hygroscopic growth factors in each particle size category (40, 80, 110, 150, and 200nm) at different RH (80–91%) during Case II were higher than those during Case I. Under the same water vapor conditions, aerosol hygroscopic growth was one of the major factors contributing to heavy haze pollution. Concerning aerosol chemical composition, nitrate was the primary component contributing to aerosol hygroscopicity over Xingtai.

Description: A small and portable incoherent broadband cavity enhanced absorption spectrometer (IBBCEAS) for the dinitrogen pentoxide (N2O5) measurement has been developed. The instrument is featured with a mechanically aligned nonadjustable optical mounting system. To minimize the influence of the aerosol extinction and strong nonlinear absorption by water vapor, a dynamic reference spectrum with NO titration is used for the spectrum analysis. The range of spectrum fitting is 640–680 nm. Moreover, the wall losses of NO3 and N2O5 on the surface of the inlet and cavity tubes were extensively characterized. We determined that the surface reactivity for the heated PFA materials toward NO3 and N2O5 is 0.16 s−1 ± 0.04 s−1 and 0.019 s−1 ± 0.004 s−1, respectively. The N2O5 transmission efficiencies over the filter is 93 % (± 3 %). For the typical field experimental set up we used, the total transmission efficiency is about 82.9 %, the optimal limit of the detection (LOD) is estimated as 1.9 ppt (1σ) at 50 s intervals, the total uncertainty of the N2O5 measurement is 15 %, which is dominated by the uncertainty of the NO3 cross section calculated for 353 K in this system. Our instrument has been successfully deployed in two comprehensive field campaigns conducted in northern rural areas of Beijing in 2016. In both campaigns, the new design of the optical mounting system enabled us a fast setup and stable running of the IBBCEAS system for the detection of N2O5. High concentrations of N2O5. up to 1 ppb were detected for the two campaigns indicating an active nighttime chemistry presented in rural Beijing.

Description: The study of aerosol optical properties is essential to understand its impact on the global climate. In our recent field measurement carried out in the Gehu area of southwest Changzhou City, a photoacoustic extinctiometer (PAX) and a cavity attenuated phase shift albedo monitor (CAPS-ALB) were used for online aerosol optical properties measurement. Laboratory calibration with gas and particle samples were carried out to correct disagreements of field measurements. During particle calibration, we adopted ammonium sulfate (AS) samples for scattering calibration of nephelometer parts of both the instruments, then combined these with number-size distribution measurements in the MIE model for calculating the value of the total scattering (extinction) coefficient. During gas calibration, we employed high concentrations of NO2 for absorption calibration of the PAX resonator and then further intercompared the extinction coefficient of CAPS-ALB with a cavity-enhanced spectrometer. The correction coefficient obtained from the laboratory calibration experiments was employed on the optical properties observed in the field measurements correspondingly and showed good results in comparison with reconstructed extinction from the IMPROVE model. The intercomparison of the calibrated optical properties of PAX and CAPS-ALB in field measurements was in good agreement with slopes of 1.052, 1.024 and 1.046 for extinction, scattering and absorption respectively, which shows the reliability of measurement results and verifies the correlation between the photoacoustic and the cavity attenuated phase shift instruments.