Using drone soundings to study the impacts and compositions of plumes from a gigantic coal-fired power plant.

The immense impacts of coal-fired power plant plumes on the atmospheric environment have caused great concern linked to climate and health issues. However, studies on the field observations of aerial plumes are relatively limited, mainly due to the lack of suitable plume observation tools and techniques. In this study, we use a multicopter unmanned aerial vehicle (UAV) sounding technique to study the influences of the aerial plumes of the world's fourth-largest coal-fired power plant on the atmospheric physical/chemical conditions and air quality. A set of species, including 106 volatile organic compounds (VOCs), CO, CO2, CH4, PM2.5, and O3, and meteorological variables of temperature (T), specific humidity (SH), and wind data, are collected by the UAV sounding technique. The results reveal that the large-scale plumes of the coal-fired power plant cause local temperature inversion and humidity changes, and even affect the dispersion of pollutants below. The chemical compositions of coal-fired power plant plumes are significantly different from those of another ubiquitous vehicular source. High fractions of ethane, ethene, and benzene and low fractions of n-butane and isopentane found in plumes could serve as the key features to help distinguish the influences of coal-fired power plant plumes from other pollution sources in a particular area. By taking the ratios of pollutants (e.g., PM2.5, CO, CH4, and VOCs) to CO2 in plumes and the CO2 emission amounts of the power plant into calculation, we enable the easy quantification of the specific pollutant emissions released from power plant plumes to the atmosphere. In summary, observation by using drone soundings dissecting the aerial plumes provides a new methodology that allows aerial plumes to be readily detected and characterized. Furthermore, the influences of the plumes on the atmospheric physical/chemical conditions and air quality can be assessed rather straightforwardly, which was not easily achievable in the past.

Characterization of odorous industrial plumes by coupling fast and slow mass spectrometry techniques for volatile organic compounds.

This study aimed to develop a technique to chemically characterize odor issues in neighborhoods of designated industrial zones with pronounced emissions of volatile organic compounds (VOCs). Due to the elusive nature of odor plumes, speedy detection with sufficient sensitivity is required to capture the plumes. In this demonstration, proton-transfer-reaction mass spectrometry (PTR-MS) was used as the front-line detection tool in an industrial zone to guide sampling canisters for in-laboratory analysis of 106 VOCs by gas chromatography-mass spectrometry/flame ionization detector (GC-MS/FID). The fast but less accurate PTR-MS coupled with the slow but accurate GC-MS/FID method effectively eliminates the drawbacks of each instrument and fortifies the strength of both when combined. A 10-day PTR-MS field screening period was conducted to determine suitable trigger VOC species with exceedingly high mixing ratios that were likely the culprits of foul odors. Twenty canister samples were then collected, triggered by m/z 43, 61 (ethyl acetate, fragments, EA), m/z 73 (methyl ethyl ketone, MEK), or m/z 88 (morpholine) in all cases. Internal consistency was confirmed by the high correlation of critical species in the PTR-MS and trigger samples. Several long-lived halocarbons were exploited as the intrinsic internal reference for quality assurance. Oxygenated VOCs (OVOCs) accounted for 15%-75% of the total VOC mixing ratios in the triggered samples. However, EA and MEK, the most prominent OVOC species, did not appear to have common sources with morpholine, which presented with PTR-MS peaks incoherent with the other OVOCs. Nevertheless, these distinctive OVOC plumes were consistent with the multiple types of odor reported by the local residents. In contrast with the triggered sampling, random samples in the same industrial zone and roadside samples in a major metropolitan area were collected. The pronounced OVOC content in the triggered samples highlighted the advantage over random grab sampling to address odor issues.

A study of the vertical homogeneity of trace gases in East Asian continental outflow.

East Asian continental outflows containing with pollutants may deteriorate air quality in the downwind region via long-range transport (LRT). In particular, cold fronts with high wind speeds generally promote the LRT of air pollutants to further downwind areas, including Taiwan. To gain an insightful understanding of the characteristics and vertical homogeneity of trace gases in East Asian continental outflows, as well as their relation with atmospheric meteorological conditions, whole air samples were collected above a cape at the northern tip of the island of Taiwan during frontal passages. Aerial samples were collected at multiple altitudes from the surface to a maximum height of 700 m with a multicopter sounding platform carrying a robotic whole air sampling device. Simultaneously, aerial meteorological variables of temperature and wind vector from near the surface to a maximum height of 1000 m were also measured during the whole air sampling periods. An array of 106 volatile organic compounds (VOCs) as well as CO, CO2, and CH4 were analyzed to characterize the air composition and vertical homogeneity of trace gases. The results revealed rather homogeneous vertical distributions of most VOCs, CO, CO2, and CH4 in the frontal passages, indicating well-mixed conditions of trace gases in the East Asian continental outflows. The strong wind shear and minimal temperature inversion associated with the frontal passage likely induced turbulence and increased vertical mixing. Furthermore, higher levels of species characteristic of the East Asian continent were observed from the surface up to hundreds of meters above the cape, revealing a strong inflow of polluted air masses from the East Asian continent brought by cold frontal passages.

Taiwan ozone trend in response to reduced domestic precursors and perennial transboundary influence.

Two decades of nitrogen oxides (NOx) and volatile organic compounds (VOCs) in ambient concentrations have been continuously reduced by nearly 60% since 1994. However, the annual mean ozone (O3) concentrations in Taiwan had leveled off for more than a decade. Furthermore, the significant cuts in precursors did lead to reduction in episodic days (O3≥ 100 ppbv) over time, implying the weakened photochemical production of O3. Simultaneously, the number of low O3 days (O3 < 20 ppbv) also decreased due to weakened NO titration. Nevertheless, the reduction of both high and low O3 days resulted in an increase in the number of medium O3 days (O3 from 60-80 ppbv). While the nighttime mean O3 continued to increase, the daytime mean O3 leveled off and coincided with the marine background concentration of approximately 40 ppbv, revealing a gradual decrease in the daytime-nighttime mean O3 difference. In addition to multiple chemical reasons, transboundary O3 from Asian continental outflow is thought to be another major contributor to the prolonged leveling of domestic O3. To quantitatively illustrate the role of the transboundary effect, model simulations were conducted in two ways: one assessed the time percentage of a year affected by the transboundary influence; and the other involved decoupling the transboundary O3 from the domestically produced O3 to quantify the amount of domestic O3 that can be mitigated by prescribing scenarios; namely, the so-called sensitivity test. The sensitivity test suggests that although controlling domestic emissions is still vital to contain O3 under weak transboundary conditions, the overall O3 averages and the long-term trend at the island scale are closely associated with the transboundary influence. The gradual increased medium O3 concentrations to approximate the marine background level could imply that future O3 concentration on the island will be more influenced more by the transboundary conditions and less relevant to the domestic containment measures.

Two-dimensional gas chromatography with electron capture detection for the analysis of atmospheric ozone depleting halocarbons.

This study is to develop a GC×GC method with electron capture detection (ECD) to analyze atmospheric halocarbons in the concentration range of parts per trillion by volume (pptv). To enrich atmospheric halocarbons a home-built thermal desorption (TD) device was coupled to the GC×GC-ECD. The technique of flow modulation was adopted using a Deans switch for GC×GC. Several column combinations of first and second dimensions were tested and the column set of DB-5×TG-1301 was found to show the best orthogonality for halocarbons. A series of modulation parameters were tested for their optimal settings. The modulation period (PM) was found to have minimal wrap-around when set at 3s. The modulation ratio (MR) was determined to be 7.82 to ensure reproducible results and maximum sensitivity. The modulation duty cycle (DC) was calculated to be approximately 0.17. Nine halocarbons were separated successfully and seven were calibrated with the use of a certified standard gas mixture. The correlation coefficients (R2) were greater than 0.9972. The reproducibility was better than 1.90% as expressed in relative standard deviation (RSD; N=30) and the detection limits were in the range of pptv for the target halocarbons. A field test by continuous analyzing ambient air with hourly resolution was performed to show the stability of the method as suggested by the homogeneity of certain halocarbons, while also reflecting concentration variation for others when emissions did arise.

Right- and left-handedness of 2(1) symmetrical herringbone assemblies of benzene.

A universal method to determine handedness of 2(1) helical assemblies composed of planar aromatic molecules is proposed and demonstrated by taking P2(1)/c and Pbca crystals of benzene, the simplest aromatic molecule, as examples.

Full-range analysis of ambient volatile organic compounds by a new trapping method and gas chromatography/mass spectrometry.

This study investigated the feasibility of analyzing a full range of ambient volatile organic compounds (VOCs) from C(3) to C(12) using gas chromatograph mass spectrometry (GC/MS) coupled with thermal desorption. Two columns were used: a PLOT column separated compounds lighter than C(6) and a DB-1 column separated C(6)-C(12) compounds. An innovative heart-cut technique based on the Deans switch was configured to combine the two column outflows at the ends of the columns before entering the MS. To prevent the resolved peaks from re-converging after combining, two techniques were attempted (hold-up vs. back-flush) to achieve the intended "delayed" elution of heavier components. Thus, the resulting chromatogram covering the full range of VOCs is a combination of two separate elutions, with the heavier section following the lighter section. With the hold-up method, band-broadening inevitably occurred for the delayed C(6)-C(7) DB-1 compounds while the light compounds eluted from the PLOT column. This broadening problem resulted in peak tailing that was largely alleviated by adding a re-focusing stage while the DB-1 compounds were back-flushed, and this modified technique is referred to as the back-flush method. With this modification, the separation of the C(6)-C(7) compounds improved dramatically, as revealed by the decrease in peak asymmetry (As) and increase in resolution. Linearity and precision for these peaks also improved, yielding R(2) and RSD values better than 0.9990 and 2.8%, respectively.