Wildland Fire Emission Sampling at Fishlake National Forest, Utah Using an Unmanned Aircraft System

Risks of Drone Use in Light of Literature Studies

This article aims to present the results of a bibliometric analysis of relevant literature and discuss the main research streams related to the topic of risks in drone applications. The methodology of the conducted research consisted of five procedural steps, including the planning of the research, conducting a systematic review of the literature, proposing a classification framework corresponding to contemporary research trends related to the risk of drone applications, and compiling the characteristics of the publications assigned to each of the highlighted thematic groups. This systematic literature review used the PRISMA method. A total of 257 documents comprising articles and conference proceedings were analysed. On this basis, eight thematic categories related to the use of drones and the risks associated with their operation were distinguished. Due to the high content within two of these categories, a further division into subcategories was proposed to illustrate the research topics better. The conducted investigation made it possible to identify the current research trends related to the risk of drone use and pointed out the existing research gaps, both in the area of risk assessment methodology and in its application areas. The results obtained from the analysis can provide interesting material for both industry and academia.

Bacterial Emission Factors: A Foundation for the Terrestrial-Atmospheric Modeling of Bacteria Aerosolized by Wildland Fires

Wildland fire is a major global driver in the exchange of aerosols between terrestrial environments and the atmosphere. This exchange is commonly quantified using emission factors or the mass of a pollutant emitted per mass of fuel burned. However, emission factors for microbes aerosolized by fire have yet to be determined. Using bacterial cell concentrations collected on unmanned aircraft systems over forest fires in Utah, USA, we determine bacterial emission factors (BEFs) for the first time. We estimate that 1.39 × 1010 and 7.68 × 1011 microbes are emitted for each Mg of biomass consumed in fires burning thinning residues and intact forests, respectively. These emissions exceed estimates of background bacterial emissions in other studies by 3-4 orders of magnitude. For the ∼2631 ha of similar forests in the Fishlake National Forest that burn each year on average, an estimated 1.35 × 1017 cells or 8.1 kg of bacterial biomass were emitted. BEFs were then used to parametrize a computationally scalable particle transport model that predicted over 99% of the emitted cells were transported beyond the 17.25 x 17.25 km model domain. BEFs can be used to expand understanding of global wildfire microbial emissions and their potential consequences to ecosystems, the atmosphere, and humans.

Los Angeles Basin's air quality transformation: a long-term investigation on the impacts of PM regulations on the trends of ultrafine particles and co-pollutants

This study investigates the long-term trends of ambient ultrafine particles (UFPs) and associated airborne pollutants in the Los Angeles Basin from 2007 to 2022, focusing on the indirect effects of regulations on UFP levels. The particle number concentration (PNC) of UFPs was compiled from previous studies in the area, and associated co-pollutant data, including nitrogen oxides (NOx), carbon monoxide (CO), elemental carbon (EC), organic carbon (OC), and ozone (O3), were obtained from the chemical speciation network (CSN) database. Over the study period, a general decrease was noted in the PNC of UFPs, NOx, EC, and OC, except for CO, the concentration trends of which did not exhibit a consistent pattern. UFPs, NOx, EC, and OC were positively correlated, while O3 had a negative correlation, especially with NOx. Our analysis discerned two distinct subperiods in pollutant trends: 2007-2015 and 2016-2022. For example, there was an overall decrease in the PNC of UFPs at an annual rate of -850.09 particles/cm3/year. This rate was more pronounced during the first sub-period (2007-2015) at -1814.9 particles/cm3/year and then slowed to -227.21 particles/cm3/year in the second sub-period (2016-2023). The first sub-period (2007-2015) significantly influenced pollutant level changes, exhibiting more pronounced and statistically significant changes than the second sub-period (2016-2022). Since 2016, almost all primary pollutants have stabilized, indicating a reduced impact of current regulations, and emphasizing the need for stricter standards. In addition, the study included an analysis of Vehicle Miles Traveled (VMT) trends from 2007 to 2022 within the Los Angeles Basin. Despite the general increase in VMT, current regulations and cleaner technologies seem to have successfully mitigated the potential increase in increase in PNC. Overall, while a decline in UFPs and co-pollutant levels was observed, the apparent stabilization of these levels underscores the need for more stringent regulatory measures and advanced emission standards.

State of the Art and Future Perspectives of Atmospheric Chemical Sensing Using Unmanned Aerial Vehicles: A Bibliometric Analysis

In recent years, unmanned aerial vehicles (UAVs) have been increasingly used to monitor and assess air quality. The interest in the application of UAVs in monitoring air pollutants and greenhouse gases is evidenced by the recent emergence of sensors with the most diverse specifications designed for UAVs or even UAVs designed with integrated sensors. The objective of this study was to conduct a comprehensive review based on bibliometrics to identify dynamics and possible trends in scientific production on UAV-based sensors to monitor air quality. A bibliometric analysis was carried out in the VOSViewer software (version 1.6.17) from the Scopus and Web of Science reference databases in the period between 2012 and 2022. The main countries, journals, scientific organizations, researchers and co-citation networks with greater relevance for the study area were highlighted. The literature, in general, has grown rapidly and has attracted enormous attention in the last 5 years, as indicated by the increase in articles after 2017. It was possible to notice the rapid development of sensors, resulting in smaller and lighter devices, with greater sensitivity and capacity for remote work. Overall, this analysis summarizes the evolution of UAV-based sensors and their applications, providing valuable information to researchers and developers of UAV-based sensors to monitor air pollutants.

Seasonal Emission Factors from Rangeland Prescribed Burns in the Kansas Flint Hills Grasslands

Operational-sized prescribed grassland burns at three mid-West U.S. locations and ten 1-ha-sized prescribed grassland burns were conducted in the Flint Hills of Kansas to determine emission factors and their potential seasonal effects. Ground-, aerostat-, and unmanned aircraft system-based platforms were used to sample plume emissions for a range of gaseous and particulate pollutants. The ten co-located, 1-ha-sized plots allowed for testing five plots in the spring and five in the late summer, allowing for control of vegetation type, biomass loading, climate history, and land use. The operational-sized burns provided a range of conditions under which to determine emission factors relevant to the Flint Hills grasslands. The 1-ha plots showed that emission factors for pollutants such as PM_2.5 and BTEX (benzene, toluene, ethylbenzene, and xylene) were higher during the late summer than during the traditional spring burn season. This is likely due to increased biomass density and fuel moisture in the growing season biomass resulting in reduced combustion efficiency.

Heat release rate of enhanced large-scale open oil slick fires with Outdoor Gas Emission Sampling (OGES) system

The Outdoor Gas Emission Sampling (OGES) system was developed to serve as an economical alternative to expensive industrial gas monitoring equipment. By establishing a sampling plane with four discrete sampling points along the radial direction of the smoke plume, the heat release rate (HRR) was measured for large-scale open oil slick fires. This newfound technique was particularly noteworthy during enhanced burns involving Flame Refluxer™ technology, where it is believed that partial premixing of the fuel and air by the apparatus resulted in a higher HRR than existing flame height correlations would suggest, evident by the HRR calculated using mass burning rate and gas analysis methods, which were in good agreement. Results from OGES show the potential of using point sampling within the plume regime to measure the HRR of fires that exceed the capabilities of conventional hood-based calorimeters, especially when it pertains to large-scale open burns.

The fingerprint stability of the biomarker hopanes and steranes in soot emissions from in-situ burning of oil

The behavior of emissions is an important concern of in-situ burning (ISB) of spilled oils. In particular, the heavy soot originated from ISB can negatively impact the atmospheric environment. To track the behavior of ISB soot, the conservative biomarkers, such as hopanes and steranes, can be potentially used. In this study, the stability of chemical fingerprints of hopanes and steranes in the ISB soot were investigated based on the burning of two different types of oils, including one ultra-light condensate (i.e., surrogate Sanchi condensate) and one heavy oil. The results indicate that the chromatographic patterns and diagnostic ratios of hopanes and steranes in the ISB soot emissions almost remain identical to their corresponding source oils, proving the various oil source identification of ISB soot can be realized. This work attempts to provide novel insights into the application of biomarkers in the management of ISB emissions.

Development and Calibration of Pressure-Temperature-Humidity (PTH) Probes for Distributed Atmospheric Monitoring Using Unmanned Aircraft Systems

Small unmanned aircraft systems (UAS) are increasingly being used for meteorology and atmospheric monitoring. The ease of deployment makes distributed sensing of parameters such as barometric pressure, temperature, and relative humidity in the lower atmospheric boundary layer feasible. However, constraints on payload size and weight, and to a lesser extent power, limit the types of sensors that can be deployed. The objective of this work was to develop a miniature pressure-temperature-humidity (PTH) probe for UAS integration. A set of eight PTH probes were fabricated and calibrated/validated using an environmental chamber. An automated routine was developed to facilitate calibration and validation from a large set of temperature and relative humidity setpoints. Linear regression was used to apply temperature and relative humidity calibrations. Barometric pressure was calibrated using a 1-point method consisting of an offset. The resulting PTH probes were less than 4 g in mass and consumed less than 1 mA when operated from a 5 VDC source. Measurements were transmitted as a formatted string in ASCII format at 1 Hz over a 3.3 V TTL UART. Prior to calibration, measurements between individual PTH probes were significantly different. After calibration, no significant differences in temperature measurements across all PTH probes were observed, and the level of significance between PTH probes was reduced. Actual differences between calibrated PTH probes were likely to be negligible for most UAS-based applications, regardless of significance. RMSE across all calibrated PTH probes for the pressure, temperature, and relative humidity was less than 31 Pa, 0.13 °C, and 0.8% RH, respectively. The resulting calibrated PTH probes will improve the ability to quantify small variations in ambient conditions during coordinated multi-UAS flights.

Wildland fire smoke alters the composition, diversity, and potential atmospheric function of microbial life in the aerobiome

The atmosphere contains a diverse reservoir of microbes but the sources and factors contributing to microbial aerosol variability are not well constrained. To advance understanding of microbial emissions in wildfire smoke, we used unmanned aircraft systems to analyze the aerosols above high-intensity forest fires in the western United States. Our results show that samples of the smoke contained ~four-fold higher concentrations of cells (1.02 ± 0.26 × 105 m-3) compared to background air, with 78% of microbes in smoke inferred to be viable. Fivefold higher taxon richness and ~threefold enrichment of ice nucleating particle concentrations in smoke implies that wildfires are an important source of diverse bacteria and fungi as well as meteorologically relevant aerosols. We estimate that such fires emit 3.71 × 1014 microbial cells ha-1 under typical wildfire conditions in western US forests and demonstrate that wildland biomass combustion has a large-scale influence on the local atmospheric microbial assemblages. Given the long-range transport of wildfire smoke emissions, these results expand the concept of a wildfire's perimeter of biological impact and have implications to biogeography, gene flow, the dispersal of plant, animal, and human pathogens, and meteorology.

Vertical profiling of black carbon and ozone using a multicopter unmanned aerial vehicle (UAV) in urban Shenzhen of South China

Existing studies on vertical profiling of black carbon (BC) and ozone (O₃) were mainly conducted in the rural areas, leading to limited knowledge of their vertical distributions in the urban area. To fill this knowledge gap, vertical profiling (0-500 m and 0-900 m, AGL) of BC and O₃ was conducted in a highly urbanized area of Shenzhen in subtropical South China using a multicopter unmanned aerial vehicle (UAV) platform. In total 32 flights were conducted from the 10th to 15th, December 2017 (winter campaign) and 42 flights from the 19th to 28th, August 2018 (summer campaign) with 4 time slots per day, including morning, afternoon, evening, and midnight. In general, equivalent BC (eBC) concentration decreased as the height increased with an overall slope of -0.13 μg m^-3 per 100 m in the winter campaign and -0.08 μg m^-3 per 100 m in the summer campaign. On the contrary, an increase of O₃ level with altitude was observed (7.8 ppb per 100 m). Absorption Ångström exponent (AAE) exhibits a slightly increasing trend with height. Seasonality of eBC vertical profiles was observed in morning, afternoon and midnight flights, but not for evening flights. The analysis showed the shape of vertical profiles of eBC and O₃ can be affected by planetary boundary layer height (PBLH) and air mass origin. Calculated heating rates due to BC show distinct seasonal variability for morning but not for afternoon, because of the counteracting effects by solar irradiance in the subtropical afternoon and eBC concentration in urban South China influenced by the monsoon climate.