ALBERT

Description: Microseismic signals are generally considered to follow the Gauss distribution. A comparison of the dynamic characteristics of sample variance and the symmetry of microseismic signals with the signals which follow α-stable distribution reveals that the microseismic signals have obvious pulse characteristics and that the probability density curve of the microseismic signal is approximately symmetric. Thus, the hypothesis that microseismic signals follow the symmetric α-stable distribution is proposed. On the premise of this hypothesis, the characteristic exponent α of the microseismic signals is obtained by utilizing the fractional low-order statistics, and then a new method of time difference of arrival (TDOA) estimation of microseismic signals based on fractional low-order covariance (FLOC) is proposed. Upon applying this method to the TDOA estimation of Ricker wavelet simulation signals and real microseismic signals, experimental results show that the FLOC method, which is based on the assumption of the symmetric α-stable distribution, leads to enhanced spatial resolution of the TDOA estimation relative to the generalized cross correlation (GCC) method, which is based on the assumption of the Gaussian distribution.

Description: Diurnal fluctuations in seawater temperature are ubiquitous on tropical reef flats. However, effects of such dynamic temperature variations on the early stages of corals are poorly understood. Here, we investigated the responses of larvae and new spats of Pocillopora damicornis to two constant temperature treatments (29 and 31 °C), and two diurnally fluctuating treatments (28–31 and 30–33 °C with daily means of 29 and 31 °C, respectively) simulating the 3 °C diel oscillations at 3 m depth on Luhuitou fringing reef (Sanya, China). Results showed that the thermal stress on settlement at 31 °C was almost negated by the fluctuating treatment. Further, temperature fluctuations did not exacerbate bleaching responses but alleviated the maximum excitation pressure over photosystem Ⅱ (PSⅡ). Although early growth and development were highly stimulated at 31 °C, oscillations of 3 °C had little effects on budding and lateral growth. Nevertheless, daytime encounters with the maximum temperature of 33 °C elicited a notable reduction in calcification. These results underscore the complexity in the effects caused by diel temperature fluctuations on early stages of corals, and suggest that the ecologically relevant temperature variability could buffer the warming stress on larval settlement and dampen the positive effects of increased temperatures on coral growth.

Description: Secondary organic aerosol (SOA) formation from biogenic precursors is affected by anthropogenic emissions, which are not well understood in polluted areas. In this study, we accomplished a year-round campaign at nine sites in polluted areas located in the Pearl River Delta (PRD) region during 2015. We measured typical biogenic SOA (BSOA) tracers from isoprene, monoterpenes, and β-caryophyllene, as well as major gaseous and particulate pollutants and investigated the impact of anthropogenic pollutants on BSOA formation. The concentrations of BSOA tracers were in the range of 45.4 to 109 ng m−3 with the majority composed of products from monoterpenes (SOAM, 47.2±9.29 ng m−3), isoprene (SOAI, 23.1±10.8 ng m−3), and β-caryophyllene (SOAC, 3.85±1.75 ng m−3). We found that atmospheric oxidants, Ox (O3 plus NO2), and sulfate correlated well with later-generation SOAM tracers, but this was not the case for first-generation SOAM products. This suggested that high Ox and sulfate levels could promote the formation of later-generation SOAM products, which probably led to the relatively aged SOAM that we observed in the PRD. For the SOAI tracers, both 2-methylglyceric acid (NO/NO2-channel product) and the ratio of 2-methylglyceric acid to 2-methyltetrols (HO2-channel products) exhibit NOx dependence, indicating the significant impact of NOx on SOAI formation pathways. The SOAC tracer was elevated in winter at all sites and was positively correlated with levoglucosan, Ox, and sulfate. Thus, the unexpected increase in SOAC in wintertime might be highly associated with the enhancement of biomass burning, O3 chemistry, and the sulfate component in the PRD. The BSOAs that were estimated using the SOA tracer approach showed the highest concentration in fall and the lowest concentration in spring with an annual average concentration of 1.68±0.40 µg m−3. SOAM dominated the BSOA mass all year round. We also found that BSOA correlated well with sulfate and Ox. This implied a significant effect from anthropogenic pollutants on BSOA formation and highlighted that we could reduce BSOA by controlling the anthropogenic emissions of sulfate and Ox precursors in polluted regions.

Description: Diurnal fluctuations in seawater temperature are ubiquitous on tropical reef flats. However, the effects of such dynamic temperature variations on the early stages of corals are poorly understood. In this study, we investigated the responses of larvae and new recruits of Pocillopora damicornis to two constant temperature treatments (29 and 31 °C) and two diurnally fluctuating treatments (28–31 and 30–33 °C with daily means of 29 and 31 °C, respectively) simulating the 3 °C diel oscillations at 3 m depth on the Luhuitou fringing reef (Sanya, China). Results showed that the thermal stress on settlement at 31 °C was almost negated by the fluctuating treatment. Further, neither elevated temperature nor temperature fluctuations caused bleaching responses in recruits, while the maximum excitation pressure over photosystem II (PSII) was reduced under fluctuating temperatures. Although early growth and development were highly stimulated at 31 °C, oscillations of 3 °C had little effects on budding and lateral growth at either mean temperature. Nevertheless, daytime encounters with the maximum temperature of 33 °C in fluctuating 31 °C elicited a notable reduction in calcification compared to constant 31 °C. These results underscore the complexity of the effects caused by diel temperature fluctuations on early stages of corals and suggest that ecologically relevant temperature variability could buffer warming stress on larval settlement and dampen the positive effects of increased temperatures on coral growth.

Description: Secondary organic aerosol (SOA) formation from biogenic precursors is affected by anthropogenic emissions, which is not well understood in polluted areas. In the study, we accomplished a year-round campaign at nine sites in the polluted areas located in Pearl River Delta (PRD) region during 2015. We measured typical biogenic SOA (BSOA) tracers from isoprene, monoterpenes, and β-caryophyllene as well as major gaseous and particulate pollutants and investigated the impact of anthropogenic pollutants on BSOA formation. The concentrations of BSOA tracers were in the range of 45.4 to 109 ng m−3 with the majority composed of products from monoterpenes (SOAM, 47.2 ± 9.29 ng m−3), followed by isoprene (SOAI, 23.1 ± 10.8 ng m−3), and β-caryophyllene (SOAC, 3.85 ± 1.75 ng m−3). We found that atmospheric oxidants, Ox (O3 plus NO2), and sulfate correlated well with high-generation SOAM tracers, but not so for first-generation SOAM products. This suggested that high Ox and sulfate could promote the formation of high-generation SOAM products, which probably led to relatively aged SOAM we observed in the PRD. For the SOAI tracers, not only 2-methylglyceric acid (NO/NO2-channel product), but also the ratio of 2-methylglyceric acid to 2-methyltetrols (HO2-channel products) exhibit NOx dependence, indicating the significant impact of NOx on SOAI formation pathways. The SOAC tracer elevated in winter at all sites and positively correlated with levoglucosan, Ox, and sulfate. Thus, the unexpected increase of SOAC in wintertime might be highly associated with the enhancement of biomass burning, atmospheric oxidation capacity and sulfate components in the PRD. The BSOAs that were estimated by the SOA tracer approach showed the highest concentration in fall and the lowest concentration in spring with an annual average concentration of 1.68 ± 0.40 μg m−3. SOAM dominated the BSOA mass all year round. We also found that BSOA correlated well with sulfate and Ox. This implicated the significant effects of anthropogenic pollutants on BSOA formation and highlighted that we could reduce the BSOA through controlling on the anthropogenic emissions of sulfate and Ox precursors in polluted regions.

Description: Volatile organic compound (VOC) control is an important issue of air quality management in Hong Kong because ozone formation is generally VOC limited. Several oxygenated volatile organic compound (OVOC) and VOC measurement techniques – namely, (1) offline 2,4-dinitrophenylhydrazine (DNPH) cartridge sampling followed by high-performance liquid chromatography (HPLC) analysis; (2) online gas chromatography (GC) with flame ionization detection (FID); and (3) offline canister sampling followed by GC with mass spectrometer detection (MSD), FID, and electron capture detection (ECD) – were applied during this study. For the first time, the proton transfer reaction–mass spectrometry (PTR-MS) technique was also introduced to measured OVOCs and VOCs in an urban roadside area of Hong Kong. The integrated effect of ambient relative humidity (RH) and temperature (T) on formaldehyde measurements by PTR-MS was explored in this study. A Poly 2-D regression was found to be the best nonlinear surface simulation (r  =  0.97) of the experimental reaction rate coefficient ratio, ambient RH, and T for formaldehyde measurement. This correction method was found to be better than correcting formaldehyde concentrations directly via the absolute humidity of inlet sample, based on a 2-year field sampling campaign at Mong Kok (MK) in Hong Kong. For OVOC species, formaldehyde, acetaldehyde, acetone, and MEK showed good agreements between PTR-MS and DNPH-HPLC with slopes of 1.00, 1.10, 0.76, and 0.88, respectively, and correlation coefficients of 0.79, 0.75, 0.60, and 0.93, respectively. Overall, fair agreements were found between PTR-MS and online GC-FID for benzene (slope  =  1.23, r  =  0.95), toluene (slope  =  1.01, r  =  0.96) and C2-benzenes (slope  =  1.02, r  =  0.96) after correcting benzene and C2-benzenes levels which could be affected by fragments formed from ethylbenzene. For the intercomparisons between PTR-MS and offline canister measurements by GC-MSD/FID/ECD, benzene showed good agreement, with a slope of 1.05 (r  =  0.62), though PTR-MS had lower values for toluene and C2-benzenes with slopes of 0.78 (r  =  0.96) and 0.67 (r  =  0.92), respectively. All in all, the PTR-MS instrument is suitable for OVOC and VOC measurements in urban roadside areas.

Description: Volatile organic compound (VOC) control is an important issue of air quality management in Hong Kong because ozone formation is generally VOC limited. Several oxygenated volatile organic compound (OVOC) and VOC measurement techniques, namely, (1) off-line 2,4-dinitrophenylhydrazine (DNPH) cartridge sampling followed by High Performance Liquid Chromatography (HPLC) analysis, (2) on-line gas chromatography (GC) with flame ionization detection (FID), and (3) off-line canister sampling followed by GC with mass spectrometer detection (MSD), FID, and (electron capture detection) ECD, were applied during this study. For the first time, the proton transfer reaction–mass spectrometry (PTR-MS) technique was also introduced to measured OVOCs and VOC in urban roadside area of Hong Kong. The integrated effect of ambient relative humidity (RH) and temperature (T) on formaldehyde measurements by PTR-MS was explored in this study. A Poly 2-D regression was found to be the best nonlinear surface simulation (r = 0.97) of the experimental reaction rate coefficient ratio, ambient RH and T for formaldehyde measurement. This correction method was found to be better than correcting formaldehyde concentrations directly via the absolute humidity of inlet sample, based on a two-year field sampling campaign at Mong Kok (MK) in Hong Kong. For OVOC species, formaldehyde, acetaldehyde, acetone and MEK showed good agreements between PTR-MS and DNPH-HPLC with with slopes of 1.00, 1.10, 0.76 and 0.88, respectively, and correlation coefficients of 0.79, 0.75, 0.60 and 0.93, respectively. Overall, fair agreements were found between PTR-MS and on-line GC- FID for benzene (slope = 1.23, r = 0.95), toluene (slope = 1.01, r = 0.96) and C2-benzenes (slope = 1.02, r = 0.96) after correcting benzene and C2-benzenes levels which could be affected by fragments formed from ethylbenzene. For the inter-comparisons between PTR-MS and off-line canister measurements by GC-MSD/FID/ECD, benzene showed good agreement with a slope of 1.05 (r = 0.62), though PTR-MS had lower values for toluene and C2-benzenes with slopes of 0.78 (r = 0.96) and 0.67 (r = 0.92), respectively. All in all, the PTR-MS instrument is suitable for OVOC and VOC measurements in urban roadside areas.