Measurement of the vertical distributions of atmospheric pollutants using an uncrewed aerial vehicle platform in Xi'an, China.

Vertical observations of atmospheric pollutants play crucial roles in a comprehensive understanding of the distribution characteristics and transport of atmospheric pollutants. A hexacopter uncrewed aerial vehicle equipped with miniature monitors was employed to measure the vertical distribution of atmospheric pollutants within a height of 1000 m at a rural site in Xi'an, China, in 2021. The concentrations of carbon monoxide (CO) and particulate matter (PM) showed generally decreasing trends with increasing height. The ozone (O3) concentration showed a general increasing trend with height followed by a gradual decreasing trend. Vertical decrements of PM2.5 and CO from 0 to 1000 m were significantly (p < 0.05) lower on observation days during summer (14.0 ± 8.1 µg m-3 and 8.7 ± 6.6 ppb, respectively), compared with those in winter (78.3 ± 14.1 µg m-3 and 34.8 ± 17.3 ppb, respectively). The horizontal transport of PM and CO mostly occurred in the morning and at night during winter observations at an altitude of 400-500 m. During the winter haze, the PM and CO profile concentrations below 500 m increased substantially with the decrease in the height of the thermal inversion layer. Vertical O3 transportation was observed in the afternoon and evening during summer, and a ∼37.7% (11.6 ppb) increase in ground-level O3 was observed in relation to vertical transport from the upper atmosphere. The results provide insights into the vertical distribution and transport of atmospheric pollutants in rural areas near cities.

Elucidating contributions of volatile organic compounds to ozone formation using random forest during COVID-19 pandemic: A case study in China.

Ozone has been reported to increase despite nitrogen oxides reductions during the COVID-19 pandemic, and ozone formation needs to be revisited using volatile organic compounds (VOCs), which are rarely measured during the pandemic. Here, a total of 98 VOCs species were monitored in an economy-active city in China from January 2021 to August 2022 to assess contributions to ozone formation during the pandemic. Total VOCs concentrations were 35.55 ± 21.47 ppb during the entire period, among which alkanes account for the largest fraction (13.78 ppb, 38.0%), followed by aromatics (6.16 ppb, 16.8%) and oxygenated VOCs (OVOCs, 5.69 ppb, 15.7%). Most VOCs groups (e.g., alkenes, OVOCs) and individual species (e.g., isoprene, methyl vinyl ketone) display obvious seasonal and diurnal variations, which are related to their sources and reactivities. No weekend effects of VOCs suggest limited influences from traffic emissions during pandemic. Aromatics and alkenes are the major contributors (39% and 33%) to ozone formation potential, largely driven by o/m/p-xylene (21%), ethylene (15%), toluene (9%). Secondary organic aerosol formation potential is dominated by toluene (>50%) despite its low proportion (5%). Further inclusion of VOCs and meteorology in the Random Forest model shows good ozone prediction performance (R2 = 0.77-0.86, RMSE = 11.95-19.91 µg/m3, MAE = 8.89-14.58 µg/m3). VOCs and NO2 contribute >50% of total importance with the largest difference in importance ratio of VOCs/NO2 in the summer and winter, implying ozone formation regime may vary. No seasonal variations in importance of meteorology are observed, while importance of other variables (e.g., PM2.5) is highest in the summer. This work identifies critical VOCs groups and species for ozone formation during the pandemic, and demonstrates the feasibility of machine learning algorithms in elucidation of ozone formation mechanisms.

A novel method for production of nitrogen fertilizer with low energy consumption by efficiently adsorbing and separating waste ammonia.

Recovering waste NH3 to be used as a source of nitrogen fertilizer or liquid fuel has recently attracted much attention. Current methods mainly utilize activated carbon or metal-organic frameworks to capture NH3, but are limited due to low NH3 adsorption capacity and high cost, respectively. In this study, novel porous materials that are low cost and easy to synthesize were prepared as NH3 adsorbents by precipitation polymerization with acid optimization. The results showed that adsorption sites (‒COOH, -OH, and lactone) which form chemical adsorption or hydrogen bonds with NH3 were successfully regulated by response surface methods. Correspondingly, the dynamic NH3 adsorption capacity increased from 5.45 mg g-1 to 129 mg g-1, which is higher than most known activated carbon and metal-organic frameworks. Separation performance tests showed that NH3 could also be separated from CO2 and CH4. The findings in this study will advance the industrialization of NH3 polymer adsorbents and provide technical support for the recycling of waste NH3.

The complexation of atmospheric Brown carbon surrogates on the generation of hydroxyl radical from transition metals in simulated lung fluid.

Atmospheric particulate matter (PM) poses great adverse effects through the production of reactive oxygen species (ROS). Various components in PM are acknowledged to induce ROS formation, while the interactions among chemicals remain to be elucidated. Here, we systematically investigate the influence of Brown carbon (BrC) surrogates (e.g., imidazoles, nitrocatechols and humic acid) on hydroxyl radical (OH) generation from transition metals (TMs) in simulated lung fluid. Present results show that BrC has an antagonism (interaction factor: 20-90 %) with Cu2+ in OH generation upon the interaction with glutathione, in which the concentrations of BrC and TMs influence the extent of antagonism. Rapid OH generation in glutathione is observed for Fe2+, while OH formation is very little for Fe3+. The compositions of antioxidants (e.g., glutathione, ascorbate, urate), resembling the upper and lower respiratory tract, respond differently to BrC and TMs (Cu2+, Fe2+ and Fe3+) in OH generation and the degree of antagonism. The complexation equilibrium constants and site numbers between Cu2+ and humic acid were further analyzed using fluorescence quenching experiments. Possible complexation products among TMs, 4-nitrocatechol and glutathione were also identified using quadropule-time-of-flight mass spectrometry. The results suggest atmospheric BrC widely participate in complexation with TMs which influence OH formation in the human lung fluid, and complexation should be considered in evaluating ROS formation mediated by ambient PM.

Application of homemade portable gas chromatography coupled to photoionization detector for the detection of volatile organic compounds in an industrial park.

Traditional offline detection of volatile organic compounds (VOCs) requires complex and time-consuming pre-treatments including gas sampling in containers, pre-concentrations, and thermal desorption, which hinders its application in rapid VOCs monitoring. Developing a cost-effective instrument is of great importance for online measurement of VOCs. Recently, photoionization detectors (PID) are received great attention due to their fast response time and high sensitivity. This study a portable gas chromatography coupled to PID (pGC-PID) was developed and optimized experimental parameters for the application in online monitoring of VOCs at an industrial site. The sampling time, oven temperature and carrier gas flow rate were optimized as 80 s, 50 °C and 60 ml·min-1, respectively. The sampling method is direct injection. Poly tetra fluoroethylene (PTFE) filter membranes were selected to remove particulate matter from interfering with PID. The reproducibility and peak separation were good with relative standard deviations (RSD) ≤ 7%. Good linearities of 27 VOCs standard curves were achieved with R2 ≥ 0.99, and the detection limits were ≤10 ppb with the lowest being 2 ppb for 1,1,2-Trichloroethane. Finally, the pGC-PID is successfully applied in online VOCs monitoring at an industrial site. A total of 17 VOCs species was detected and their diurnal variations were well obtained, indicating pGC-PID is well suited for online analysis in field campaign.

Three-dimensional spatiotemporal variability of CO2 in suburban and urban areas of Shaoxing City in the Yangtze River Delta, China.

Metropolitan areas are the most anthropogenically active places but there is a lack of knowledge in carbon dioxide (CO2) spatial distribution in suburban and urban areas. In this study, the CO2 three-dimensional distributions were obtained from 92 times vertical unmanned aerial vehicle (UAV) flight observations in Shaoxing suburbs and 90 times ground mobile observations in Shaoxing urban areas from Nov. 2021 to Nov. 2022. The vertical distribution showed that CO2 concentrations gradually decreased from 450 to 420 ppm with altitude from 0 to 500 m. CO2 vertical profile concentrations can be influenced by transport from multiple regions. Based on the vertical observation data combining a potential source contribution function (PSCF) model, Shaoxing suburban CO2 were to be derived from urban areas in spring and autumn, while in winter and autumn were mainly from the long-transports from neighboring cities. Further the CO2 concentrations of urban horizontal distribution were observed in the range of 460-510 ppm through the mobile campaigns. Urban CO2 were partly emitted from traffic exhausts and residential combustion. Overall, CO2 concentrations were observed to be lower in spring and summer due to the CO2 uptake by plant photosynthesis. This uptake was initially quantified and accounted for 4.2 % of total CO2 in suburbs and 3.3 % in urban areas by calculating the decrease in CO2 concentration from peak to trough in the daytime. Compared with the CO2 observed in the Lin'an background station, the maximum regional CO2 enhancement in Shaoxing urban areas reached to 8.9 % while the maximum in suburbs only 4.4 %. The contribution differences between urban and suburban areas to regional CO2 were relatively constant at 1.6 % in four seasons may be mainly ascribed to the contribution of long-range CO2 transport to the suburbs.

Tracking long-term population exposure risks to PM2.5 and ozone in urban agglomerations of China 2015-2021.

China has experienced severe air pollution in the past decade, especially PM2.5 and emerging ozone pollution recently. In this study, we comprehensively analyzed long-term population exposure risks to PM2.5 and ozone in urban agglomerations of China during 2015-2021 regarding two-stage clean-air actions based on the Ministry of Ecology and the Environment (MEE) air monitoring network. Overall, the ratio of the population living in the regions exceeding the Chinese National Ambient Air Quality Standard (35 µg/m3) decreases by 29.9 % for PM2.5 from 2015 to 2021, driven by high proportions in the Middle Plain (MP, 42.3 %) and Lan-Xi (35.0 %) regions. However, this ratio almost remains unchanged for ozone and even increases by 1.5 % in the MP region. As expected, the improved air quality leads to 234.7 × 103 avoided premature mortality (ΔMort), mainly ascribed to the reduction in PM2.5 concentration. COVID-19 pandemic may influence the annual variation of PM2.5-related ΔMort as it affects the shape of the population exposure curve to become much steeper. Although all eleven urban agglomerations share stroke (43.6 %) and ischaemic heart disease (IHD, 30.1 %) as the two largest contributors to total ΔMort, cause-specific ΔMort is highly regional heterogeneous, in which ozone-related ΔMort is significantly higher (21 %) in the Tibet region than other urban agglomeration. Despite ozone-related ΔMort being one order of magnitude lower than PM2.5-related ΔMort from 2015 to 2021, ozone-related ΔMort is predicted to increase in major urban agglomerations initially along with a continuous decline for PM2.5-related ΔMort from 2020 to 2060, highlighting the importance of ozone control. Coordinated controls of PM2.5 and O3 are warranted for reducing health burdens in China during achieving carbon neutrality.

Ameliorating SERS Sensitivity for Pesticide Malathion Detection with Synergistic Boosting Effect by Hydrogen Cations and Chloride Anions.

Although SERS has been widely recognized as one of the highly sensitive analytical methods that can be deployed in the field with high sensitivity and short analysis time, reports regarding the fast determination of malathion at low concentrations are still scarce. Here, in this work, the solution pH and various halogen co-adsorbates were explored to promote the SERS signal of malathion using the citrate-reduced Ag NPs. It was found that chloride anions were the most efficient signal booster among the three halogen ions screened. Further examination of the SERS profile of the malathion in the presence of different halogen species found that the stretching mode of the P-S bond shifted to a lower frequency with Cl-, which may imply closer (and stronger) binding of malathion to the Ag NPs. This concurs with literature reports that halogen ions could facilitate the adsorption of a certain analyte onto the SERS substrate. In addition, hydrogen ions showed a synergistic effect on SERS signal enhancement when combined with chloride anions. At optimum conditions, the malathion could be detected with a limit of detection (LOD) of 3 ppb. Malathion-spiked cherry tomatoes and oranges were analyzed, and the recovery rates were found to be within 85-100%.

Characteristics and sources analysis of ambient volatile organic compounds in a typical industrial park: Implications for ozone formation in 2022 Asian Games.

In this study, volatile organic compounds (VOCs) at a major industrial park in Yangtze River Delta Region, China, along with an urban site had been investigated for three years (2018-2020). The daily-mean concentration of total 97 VOCs in the industrial park (224.3 ± 139.1 µg/m3) was about twice that of urban site (112.0 ± 64.2 µg/m3). Halohydrocarbons were predominant VOCs species at both sites accounting for 39.0 % and 32.2 % in industrial and urban sites, respectively. Annual-average concentrations of total VOCs slowed down gradually in industrial park, while that of the urban site increased annually. Evident seasonal and diurnal variations were observed for VOCs concentration in both sites. Higher VOCs concentrations appeared in summer for industrial park, and high concentrations generally appeared at 8:00 and 19:00-20:00 in two sites. Diagnostic ratios of m/p-xylene to ethylbenzene indicated vehicle emissions and solvent volatilization were main sources of VOCs in industrial site during winter. Further positive matrix factorization identified fuel usage and industry source as major sources in industrial park and urban site, respectively. Ozone formation potential calculations showed aromatics contributed most to ozone formation, and benzyl chloride was a key species when its concentration was high. Further empirical kinetic modeling approach revealed ozone formation in industrial park was in VOCs-limited regime. Through air mass trajectory analysis, air pollutants especially ozone from industrial park will be transported to stadiums by northeast wind during the 2022 Asian Games. The reductions in VOCs emissions from industrials are highly recommended for ozone control in 2022 Asian Games.

Structure and functional group regulation of plastics for efficient ammonia capture.

Activated carbon and metal organic frameworks have been tested as NH3 recovery adsorbents, however, they are limited due to low NH3 adsorption capacity and high cost, respectively. In this study, ethylene glycol dimethacrylate (EGDMA) polymers as the representative ester plastics were tested, and their structure and adsorption sites were regulated using HNO3, HCl, or H2SO4 with varied H+ concentrations. The results showed that the EGDMA polymers all used hydrolysis which promoted NH3 adsorption via different mechanisms. With HNO3 and HCl optimization, an increased surface area promoted NH3 adsorption via physical forces. H2SO4 optimization resulted in -COOH, -OH, and -SO3H formation, which reacted with NH3 by chemical adsorption and hydrogen bonds. This significantly increased the NH3 adsorption capacity (85.99 mg·g-1) compared to the material before optimization (0.36 mg·g-1). This study presents a novel low-cost and efficient method to recycle waste plastics as NH3 adsorbents.

Vertical profiles of O3, NO2 and PM in a major fine chemical industry park in the Yangtze River Delta of China detected by a sensor package on an unmanned aerial vehicle.

The vertical profiles and diurnal variations of air pollutants at different heights in the fine chemical industry park (FCIP) were systematically studied in this study. Air pollutants in a major FCIP in the Yangtze River Delta of China within 500 m above ground level (AGL) detected by a sensor package on an unmanned aerial vehicle (UAV). The air pollutants including ozone (O3), nitrogen dioxide (NO2), particulate matter (PM), total volatile organic compounds (TVOCs) and carbon monoxide (CO), respectively, had been measured through more than one hundred times of vertical flights from Aug. 2020 to Jul. 2021. The concentrations of NO2 and CO generally decreased with the height while the concentrations of O3 increased with the height within 500 m AGL. The photochemical reaction resulted in a strong inverse relationship between the vertical profiles of O3 and that of NO2. The concentrations of PM2.5 and TVOCs generally decreased with the height below 100 m AGL and were fully mixed above 100 m AGL. The vertical profiles of different particle sizes were well consistent with the R2 value of 0.97 between PM1 and PM2.5 and 0.93 between PM2.5 and PM10. The NO2 and PM2.5 concentrations sometimes increased with height maybe due to the influence of temperature inversion layer or long-distance transportation from northern China. The diurnal variations of NO2, O3, TVOCs and CO concentrations at different heights within 500 m AGL were basically consistent. The diurnal variations range of PM2.5 concentrations below 100 m AGL was large and different from other heights, which should be greatly influenced by the local emissions. The unstable atmospheric stability was accompanied by strong photochemical reactions and convective activities, resulting in low concentrations of NO2 and PM2.5, while high concentrations of O3.

Direct Measuring Particulate Matters in Smoke Plumes from Chimneys in a Textile Dyeing Industrial Park by a Self-Developed PM Detector on an UAV in Yangtze River Delta of China.

Directly measuring particulate matters (PM) from chimneys in an industrial park is difficult due to it being hard to reach the peak heights. A self-developed PM detector on an unmanned aerial vehicle (UAV) had been deployed to directly measure the PM emissions in smoke plumes from chimneys in a textile dyeing industrial park. Compared with a commercial PM device (LD-5R, SIBATA, Kyoto, Japan), the self-developed detector showed similar performance with a good correlation (R2 varying from 0.911 to 0.951) in simultaneously vertical PM measurements on UAV. The PM emissions from chimneys after different textile treating processes, including pigment printing, dyeing process, and digital printing, were investigated. PM mass concentrations and particle number concentrations (PNC) in different sizes were found to be significantly higher in pigment printing than those in dyeing process and digital printing by 2 or 3 times after electrostatic precipitation. The activated carbon adsorption and electrostatic precipitation were the major PM controlling techniques in the park. The PM mass concentrations and PNC were the highest in the process of dyeing after activated carbon adsorption with the concentrations of PM1 (1000 µg·m-3), PM2.5 (1600 µg·m-3), and PM10 (2000 µg·m-3), respectively. According to the results of PM and PNC, PM2.5 was found to be the dominant particles accounting for 99% of the PM emissions. It may be due to the high temperature in thermo-fixing machine, which is beneficial to the PM2.5 generation. This study revealed PM2.5 was the dominant particles to be reduced in textile dyeing enterprises to mitigate PM pollution.

Spatiotemporal variations of air pollutants and ozone prediction using machine learning algorithms in the Beijing-Tianjin-Hebei region from 2014 to 2021.

China was seriously affected by air pollution in the past decade, especially for particulate matter (PM) and emerging ozone pollution recently. In this study, we systematically examined the spatiotemporal variations of six air pollutants and conducted ozone prediction using machine learning (ML) algorithms in the Beijing-Tianjin-Hebei (BTH) region. The annual-average concentrations of CO, PM10, PM2.5 and SO2 decreased at a rate of 141, 11.0, 6.6 and 5.6 µg/m3/year, while a pattern of initial increase and later decrease was observed for NO2 and O3_8 h. The concentration of SO2, CO and NO2 was higher in Tangshan and Xingtai, while northern BTH region has lower levels of CO, NO2 and PM. Spatial variations of ozone were relatively small in the BTH region. Monthly variations of PM10 displayed an increase in March probably due to wind-blown dusts from Northwest China. A seasonal and diurnal pattern with summer and afternoon peaks was found for ozone, which was contrast with other pollutants. Further ML algorithms such as Random Forest (RF) model and Decision tree (DT) regression showed good ozone prediction performance (daily: R2 = 0.83 and 0.73, RMSE = 30.0 and 37.3 µg/m3, respectively; monthly: R2 = 0.93 and 0.88, RMSE = 12.1 and 15.8 µg/m3, respectively) based on 10-fold cross-validation. Both RF model and DT regression relied more on the spatial trend as higher temporal prediction performance was achieved. Solar radiation- and temperature-related variables presented high importance at daily level, whereas sea level pressure dominated at monthly level. The spatiotemporal heterogeneity in variable importance was further confirmed using case studies based on RF model. In addition, variable importance was possibly influenced by the emission reductions due to COVID-19 pandemic. Despite its possible weakness to capture ozone extremes, RF model was beneficial and suggested for predicting spatiotemporal variations of ozone in future studies.

Ethylene dimethacrylate used as an NH3 adsorbent with high adsorption capacity and selectivity.

NH3 molecularly imprinted polymers (NH3-MIPs) were synthesized that could successfully separate and recover NH3 during sludge aerobic composting; however, increased toluene usage during the adsorbent preparation incurred a high cost and severe environmental risks. The purpose of this study was to reduce toluene usage by optimizing the reagent composition of NH3-MIPs, based on maintaining a high NH3 adsorption capacity and selectivity. Five adsorbent groups, including NH3-MIPs, and NH3-Ethylene dimethacrylate adsorbents (NH3-EGDMA) with 0%, 75%, 90%, and 100% toluene reduction efficiencies, were prepared and tested for their adsorption performance. The results showed that NH3-EGDMA with 75% toluene reduction not only had a high NH3 adsorption capacity (104.42 mg g-1) but also had a high separation factor for NH3/methyl sulfide (3121) and NH3/dimethyl disulfide (4597). The adsorption mechanism was identified as a chemical force between NH3 and NH3-EGDMA with a 75% toluene reduction using the analysis of the kinetic model. This study significantly reduces NH3 adsorbent cost as well as harm to the environment during the adsorbent preparation, which was beneficial to the popularization and application of this NH3 adsorbent.

Temporal Characteristics of Ozone (O3) in the Representative City of the Yangtze River Delta: Explanatory Factors and Sensitivity Analysis.

Ozone (O3) has attracted considerable attention due to its harmful effects on the ecosystem and human health. The Yangtze River Delta (YRD), China in particular has experienced severe O3 pollution in recent years. Here, we conducted a long-term observation of O3 in YRD to reveal its characteristics. The O3 concentration in autumn was the highest at 72.76 ppb due to photochemical contribution and local convection patterns, with its lowest value of 2.40 ppb in winter. O3 exhibited strong diurnal variations, showing the highest values in the early afternoon (15:00-16:00) and the minimum in 07:00-08:00, specifically, peroxyacetyl nitrate (PAN) showed similar variations to O3 but PAN peak usually occurred 1 h earlier than that of O3 due to PAN photolysis. A generalized additive model indicated that the key factors to O3 formation were NO2, PAN, and temperature. It was found that a certain temperature rise promoted O3 formation, whereas temperatures above 27 °C inhibited O3 formation. An observation-based model showed O3 formation was VOCs-limited in spring and winter, was NOx-limited in summer, and even controlled by both VOCs and NOx in autumn. Thus, prevention and control strategies for O3 in the YRD are strongly recommended to be variable for each season based on various formation mechanisms.

Chemical Composition and Source Apportionment of Wintertime Airborne PM2.5 in Changchun, Northeastern China.

This study presents field observations and laboratory analyses of wintertime airborne particulate matter (PM2.5) and its chemical components in the Changchun metropolitan area, the geographical center of northeastern China. Twenty-four hour PM2.5 filter samples were collected from 23 December 2011 to 31 January 2012 at four sites in the types of traffic, residential, campus, and a near-city rural village, respectively. Daily PM2.5 concentrations ranged from 49 to 466 µg m-3, with an arithmetic average of 143 µg m-3. Laboratory analyses showed that among all measured chemical species, mineral dust contributed the largest proportion (20.7%) to the total PM2.5 mass, followed by secondary inorganic aerosols (SIA, including SO42-, NO3- and NH4+), which constituted 18.8% of PM2.5 mass. Another notable feature of PM2.5 chemical composition was high halogen (Cl- and F-) loadings at all sites, which was likely due to emissions from coal combustion, plastic manufacturing, and glass melting. Among the four sampling sites, the suburban site exhibited the highest PM2.5 levels and extremely high Cl- and F- loadings due to residential wood burning and nearby industrial facilities lacking effective emission controls. Our results report one of the earliest observations of PM2.5 composition in this region, providing a baseline of aerosol profiles of aerosol before PM2.5 was routinely measured by environmental protection agencies in China, which could be useful for assessing long-term trends of air quality and effectiveness of mitigation measures.

A lightweight low-cost and multipollutant sensor package for aerial observations of air pollutants in atmospheric boundary layer.

A lightweight low-cost multipollutant sensor package is particularly portable to aerial measurements and field campaign due to its light weight (2.0 kg), compact size (L × W × H, 22 × 15 × 10 cm), and low energy-consumption (20 Wa). The sensor system consists of electrochemical sensors measuring O3, NO2, NO, SO2, CO, an optical counting (OPC) particulate matter (PM) sensor for PM1.0, PM2.5, and PM10, a miniature photoionization detector (PID) for total volatile organic compounds (TVOCs), and metrological sensors for air temperature, relative humidity (RH) and air pressure. All sensor signals were collected and transferred by a data acquirement (DAQ) logger. The sensor data were saved in a microcomputer and transmitted wireless by a GSM/GPS module. All sensors and the accessories were integrated and installed in a thermal insulation foam package, of which temperature was stable at 25 °C to avoid the temperature effect. A silicone desiccant tube was connected to the inlet of air sample to minimize the RH influence. The sensor performances were compared with on-ground reference instruments for a 21-day field campaign and commercial portable instruments from Thermal Scientific and Vaisala in aerial observations. All gas sensors and PM sensor showed good correlations with the reference instruments with R2 varying from 0.81 to 0.93 and slope from 0.89 to 1.35. The O3 sensor performed best with R2 = 0.93 and slope = 1.02. In aerial measurements PM and O3 sensors obtained similar vertical profiles of PM and O3 with those obtained by commercial Thermal PTR PM monitor and Vaisala O3 sounding sensor, respectively. The sensor package was successfully deployed to observe the vertical profiles of air pollutants on a tethered balloon and to exactly locate exhaust sources in an industrial park with an unmanned aerial vehicle (UAV). Our sensor package was substantiated to be a reliable and accurate device for aerial measurements of air pollutants in atmospheric boundary layer (ABL).

Low-cost photoionization sensors as detectors in GC × GC systems designed for ambient VOC measurements.

Conventional volatile organic compound (VOC) monitoring based on thermal desorption - gas chromatography-mass spectrometry (TD-GC-MS) or gas chromatography-flame ionization detector (TD-GC-FID) is relatively cumbersome and expensive. In this study commercial off the shelf low-cost and low-power photo-ionization detector (PID) sensors are used as simple detectors in VOC analysis systems based on GC, including a miniaturised GC × GC device with portable, low-cost, and low-energy-consumption features. PID sensors produce a voltage signal positively proportional to VOC concentration, which when incorporated into a TD-GC system gave limit of detection of 0.02 ppbV for isoprene. To test PID performance in real-world applications, PID sensors were deployed as (i) a second alternative detector in a GC-Quadruple Time Of Flight Mass spectrometry (GC-Q-TOF-MS), and (ii) the main detector in a compact two-dimensional gas chromatograph (GC × GC). PID sensors with 10.6 eV and 11.7 eV lamps were used to measure eight toxic chemicals including organic sulfide and organic phosphonates via GC; two species were ionized by a 10.6 eV lamp and four species by the 11.7 eV lamp. Commercially available low-cost PIDs designed for standalone could be straightforwardly and effectively re-used as detectors in compact GC × GC systems, in this work showing excellent VOC sensitivity, fast response and low operational demands compared to comparable field instruments based on GC-FID or MS.

Analysis of biogenic carbonyl compounds in rainwater by stir bar sorptive extraction technique with chemical derivatization and gas chromatography-mass spectrometry.

Stir bar sorptive extraction is a powerful technique for the extraction and analysis of organic compounds in aqueous matrices. Carbonyl compounds are ubiquitous components in rainwater, however, it is a major challenge to accurately identify and sensitively quantify carbonyls from rainwater due to the complex matrix. A stir bar sorptive extraction technique was developed to efficiently extract carbonyls from aqueous samples following chemical derivatization by O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride. Several commercial stir bars in two sizes were used to simultaneously measure 29 carbonyls in aqueous samples with detection by gas chromatography with mass spectrometry. A 100 mL aqueous sample was extracted by stir bars and the analytes on stir bars were desorbed into a 2 mL solvent solution in an ultrasonic bath. The preconcentration Coefficient for different carbonyls varied between 30 and 45 times. The limits of detection of stir bar sorptive extraction with gas chromatography mass spectrometry for carbonyls (10-30 ng/L) were improved by ten times compared with other methods such as gas chromatography with electron capture detection and stir bar sorptive extraction with high-performance liquid chromatography and mass spectrometry. The technique was used to determine carbonyls in rainwater samples collected in York, UK, and 20 carbonyl species were quantified including glyoxal, methylglyoxal, isobutenal, 2-hydroxy ethanal.

Biogenic volatile organic compound analyses by PTR-TOF-MS: Calibration, humidity effect and reduced electric field dependency.

Green leaf volatiles (GLVs) emitted by plants after stress or damage induction are a major part of biogenic volatile organic compounds (BVOCs). Proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) is a high-resolution and sensitive technique for in situ GLV analyses, while its performance is dramatically influenced by humidity, electric field, etc. In this study the influence of gas humidity and the effect of reduced field (E/N) were examined in addition to measuring calibration curves for the GLVs. Calibration curves measured for seven of the GLVs in dry air were linear, with sensitivities ranging from 5 to 10 ncps/ppbv (normalized counts per second/parts per billion by volume). The sensitivities for most GLV analyses were found to increase by between 20% and 35% when the humidity of the sample gas was raised from 0% to 70% relative humidity (RH) at 21°C, with the exception of (E)-2-hexenol. Product ion branching ratios were also affected by humidity, with the relative abundance of the protonated molecular ions and higher mass fragment ions increasing with humidity. The effect of reduced field (E/N) on the fragmentation of GLVs was examined in the drift tube of the PTR-TOF-MS. The structurally similar GLVs are acutely susceptible to fragmentation following ionization and the fragmentation patterns are highly dependent on E/N. Overall the measured fragmentation patterns contain sufficient information to permit at least partial separation and identification of the isomeric GLVs by looking at differences in their fragmentation patterns at high and low E/N.