Fire is an imminent risk in space activities. Toxic gas and particle emissions can quickly reach dangerous levels in sealed environments. To improve smoke detection, protection, and post-fire cleanup, understanding the emissions from the pyrolysis of spacecraft-relevant materials is crucial. This study investigated the pyrolysis of four common spacecraft materials, including Kapton, polytetrafluoroethylene (PTFE), Teflon/Kapton/Teflon (TKT) wire insulation, and VelcroTM, to identify, evaluate, and quantify their gaseous and particulate emissions. Kapton emitted high levels of carbon monoxide and hydrogen cyanide, PTFE and TKT emitted multiple toxic fluorinebased gases including carbonyl fluoride and hydrogen fluoride, while VelcroTM had the highest PM2.5 emission factor. Most particles were in the submicron size range, with mode diameter peaked in the 100-200 nm range. The particles were nearly electrically neutral, carrying less than 0.15 net elementary charges per particle. Organic compounds predominated in the particle compositions.

Direct-on-Filter (DoF) analysis of respirable crystalline silica (RCS) by Fourier Transform Infrared (FTIR) spectroscopy is a useful tool for assessing exposure risks. With the RCS exposure limits becoming lower, it is important to characterize and reduce measurement uncertainties. This study systematically evaluated two filter types (i.e., polyvinyl chloride [PVC] and polytetrafluoroethylene [PTFE]) for RCS measurements by DoF FTIR spectroscopy, including the filter-to-filter and day-to-day variability of blank filter FTIR reference spectra, particle deposition patterns, filtration efficiencies, and pressure drops. For PVC filters sampled at a flow rate of 2.5 L/min for 8 h, the RCS limit of detection (LOD) was 7.4 mu g/m(3) when a designated laboratory reference filter was used to correct the absorption by the filter media. When the spectrum of the pre-sample filter (blank filter before dust sampling) was used for correction, the LOD could be up to 5.9 mu g/m(3). The PVC absorption increased linearly with reference filter mass, providing a means to correct the absorption differences between the pre-sample and reference filters. For PTFE, the LODs were 12 and 1.2 mu g/m(3) when a designated laboratory blank or the pre-sample filter spectrum was used for blank correction, respectively, indicating that using the pre-sample blank spectrum will reduce RCS quantification uncertainty. Both filter types exhibited a consistent radially symmetric deposition pattern when particles were collected using 3-piece cassettes, indicating that RCS can be quantified from a single measurement at the filter center. The most penetrating aerodynamic diameters were around 0.1 mu m with filtration efficiencies >= 98.8% across the measured particle size range with low-pressure drops (0.2-0.3 kPa) at a flow rate of 2.5 L/min. This study concludes that either the PVC or the PTFE filters are suitable for RCS analysis by DoF FTIR, but proper methods are needed to account for the variability of blank absorption among different filters.

Most evaluations of low-cost aerosol sensors have focused on their measurement bias compared to regulatory monitors. Few evaluations have applied fundamental principles of aerosol science to increase our understanding of how such sensors work and could be improved. We examined the Plantower PMS5003 sensor's internal geometry, laser properties, photodiode responses, microprocessor output, flow rates, and response to mono- and poly-disperse aerosols. We developed a physics-based model of particle light scattering within the sensor, which we used to predict counting and sizing efficiency for 0.30 to 10 mu m particles. We found that the PMS5003 counts single particle scattering events, acting like an imperfect optical particle counter, rather than a nephelometer. As particle flow is not focused into the core of the laser beam, >99% of particles that flow through the PMS5003 miss the laser, and those that intercept the laser usually miss the focal point and are subsequently undersized, resulting in erroneous size distribution data. Our model predictions of PMS5003 response to varying particle diameters, aerosol compositions, and relative humidity were consistent with laboratory data. Computational fluid dynamics simulations of the PurpleAir monitor housing showed that for wind-speeds less than 3 m s(-1), fine and coarse particles were representatively aspired to the PMS5003 inlet. Our measurements and models explain why the PurpleAir overstates regulatory PM2.5 in some locations but not others; why the PurpleAir PM10 is unresponsive to windblown dust; and why it reports a similar particle size distribution for coarse particles as it does for smoke and ambient background aerosol.

In this study, the temporal variations of black carbon (BC) were analyzed from November 2019 to September 2021, in Tacna, Peru. Ground measurements obtained with a photoacoustic extinctiometer (PAX BC) and NASA’s MERRA-2 reanalysis data (MERRA-2 BC) were used. The seasonal concentrations of PAX BC (mean ± standard deviation) were as follows: 0.70 ± 0.35, 0.73 ± 0.46, 0.70 ± 0.39, and 0.85 ± 0.46 µg m−3, for spring, summer, autumn, and winter, respectively; while MERRA-2 BC values were 0.12 ± 0.11, 0.06 ± 0.02, 0.06 ± 0.02, and 0.11 ± 0.06 µg m−3, for the same seasons. We found a large discrepancy between these two techniques, as the PAX BC measurements were an order of magnitude higher than the MERRA-2 BC values. In addition, MERRA-2 did not record urban pollution events and did not present the BC weekend effect. The most frequent wind direction (81%) was from the southwest and the sources of greatest contamination were located to the northeast and southeast. The Mann–Kendall test confirmed a downward trend in PAX BC one week (37%) and two weeks (30%) after the start of the COVID-19 lockdown, and no trend in MERRA-2 BC. These results suggest that MERRA-2 underestimates the BC emissions from local sources.

We report the first spectral photoacoustic measurements of silica, coal, and kaolinite dust absorption coefficients from 11 to 13 μm at 5 nm resolution made with a tunable quantum cascade laser. This is important because airborne silica dust and coal dust within mining environments continue to be a problem for mine workers and staff due to their severe health effects on the respiratory system, while other dust types are potentially interferents to their detection. Our real-time spectra compare favorably with the non-real-time filter-based Fourier transform infrared spectrometer (FTIR) spectra obtained using the sampling system developed by NIOSH for their end-of-shift method to determine silica dust concentrations using a portable FTIR. We discuss our new dust generation system and instrument testing chamber. We also show that our PM4 silica mass concentration measurements by a low-cost air quality sensor (SPS30) are in good agreement with the TSI Aerosol Particle Sizer instrument, the NIOSH end of shift method, gravimetric mass, and correlate well with photoacoustic light absorption measurements at a wavelength where silica absorbs strongly.

Carbonaceous aerosols emitted from biomass burning influence radiative forcing and climate change. Of particular interest are emissions from high-latitude peat burning because amplified climate change makes the large carbon mass stored in these peatlands more susceptible to wildfires and their emission can affect cryosphere albedo and air quality after undergoing transport. We combusted Siberian peat in a laboratory biomass-burning facility and characterized the optical properties of freshly emitted combustion aerosols and those photochemically aged in an oxidation flow reactor (OFR) with a three-wavelength photoacoustic instrument. Total particle count increased with aging by a factor of 6 to 11 while the total particle volume either changed little (<8%) for 19 and 44 days of equivalent aging and increased by 88% for 61 days of equivalent aging. The aerosol single-scattering albedo (SSA) of both fresh and aged aerosol increased with the increasing wavelength. The largest changes in SSA due to OFR aging were observed at the shortest of the three wavelengths (i.e., at 405 nm) where SSA increased by less than ~2.4% for 19 and 44 days of aging. These changes were due to a decrease in the absorption coefficients by ~45%, with the effect on SSA somewhat reduced by a concurrent decrease in the scattering coefficients by 20 to 25%. For 61 days of aging, we observed very little change in SSA, namely an increase of 0.31% that was caused a ~56% increase in the absorption coefficients that was more than balanced by a somewhat larger (~71%) increase in the scattering coefficients. These large increases in the absorption and scattering coefficients for aging at 7 V are at least qualitatively consistent with the large increase in the particle volume (~88%). Overall, aging shifted the absorption toward longer wavelengths and decreased the absorption Ångström exponents, which ranged from ~5 to 9. Complex refractive index retrieval yielded real and imaginary parts that increased and decreased, respectively, with the increasing wavelength. The 405 nm real parts first increased and then decreased and imaginary parts decreased during aging, with little change at other wavelengths.

The Plantower PMS5003 sensors (PMS) used in the PurpleAir monitor PA-II-SD configuration (PA-PMS) are equivalent to cell-reciprocal nephelometers using a 657 nm perpendicularly polarized light source that integrates light scattering from 18 to 166∘. Yearlong field data at the National Oceanic and Atmospheric Administration's (NOAA) Mauna Loa Observatory (MLO) and Boulder Table Mountain (BOS) sites show that the 1 h average of the PA-PMS first size channel, labeled “> 0.3 µm” (“CH1”), is highly correlated with submicrometer aerosol scattering coefficients at the 550 and 700 nm wavelengths measured by the TSI 3563 integrating nephelometer, from 0.4 to 500 Mm−1. This corresponds to an hourly average submicrometer aerosol mass concentration of approximately 0.2 to 200 µg m−3. A physical–optical model of the PMS is developed to estimate light intensity on the photodiode, accounting for angular truncation of the volume scattering function as a function of particle size. The model predicts that the PMS response to particles > 0.3 µm decreases relative to an ideal nephelometer by about 75 % for particle diameters ≥ 1.0 µm. This is a result of using a laser that is polarized, the angular truncation of the scattered light, and particle losses (e.g., due to aspiration) before reaching the laser. It is shown that CH1 is linearly proportional to the model-predicted intensity of the light scattered by particles in the PMS laser to its photodiode over 4 orders of magnitude. This is consistent with CH1 being a measure of the scattering coefficient and not the particle number concentration or particulate matter concentration. The model predictions are consistent with data from published laboratory studies which evaluated the PMS against a variety of aerosols. Predictions are then compared with yearlong fine aerosol size distribution and scattering coefficient field data at the BOS site. Field data at BOS confirm the model prediction that the ratio of CH1 to the scattering coefficient would be highest for aerosols with median scattering diameters < 0.3 µm. The PMS detects aerosols smaller than 0.3 µm diameter in proportion to their contribution to the scattering coefficient. The results of this study indicate that the PMS is not an optical particle counter and that its six size fractions are not a meaningful representation of particle size distribution. The relationship between the PMS 1 h average CH1 and bsp1, the scattering coefficient in Mm−1 due to particles below 1 µm aerodynamic diameter, at wavelength 550 nm, is found to be bsp1 = 0.015 ± 2.07 × 10−5 × CH1, for relative humidity below 40 %. The coefficient of determination r2 is 0.97. This suggests that the low-cost and widely used PA monitors can be used to measure and predict the submicron aerosol light scattering coefficient in the mid-visible nearly as well as integrating nephelometers. The effectiveness of the PA-PMS to serve as a PM2.5 mass concentration monitor is due to both the sensor behaving like an imperfect integrating nephelometer and the mass scattering efficiency of ambient PM2.5 aerosols being roughly constant.

A new instrument for the quantification of light absorption by particles collected on filters has been developed to address long standing environmental questions about light-absorbing particles in air, water, and on snow and ice. The Light Absorption Heating Method (LAHM) uses temperature changes when filters are exposed to light to quantify absorption. Through the use of calibration standards, the observed temperature response of unknown materials can be related to the absorption cross section of the substance collected on the filter. Here, we present a detailed description of the instrument and calibration. The results of the calibration tests using a common surrogate for black carbon, Fullerene soot, show that the instrument provides stable results even when exposed to adverse laboratory conditions, and that there is little drift in the instrument over longer periods of time. Calibration studies using Fullerene soot suspended in water, airborne propane soot, as well as atmospheric particulates show consistent results for absorption cross section when using accepted values for the mass absorption cross section of the soot and when compared to results from a 3-wavelength photoacoustic instrument. While filter sampling cannot provide the time resolution of other instrumentation, the LAHM instrument fills a niche where time averaging is reasonable and high-cost instrumentation is not available. The optimal range of absorption cross sections for LAHM is from 0.1 to 5.0 cm2 (~1.0–50.0 µg soot) for 25 mm filters and 0.4 to 20 cm2 (4.0–200.0 µg soot) for 47 mm filters, with reduced sensitivity to higher values.

Respirable crystalline silica (RCS) is an inhalation health hazard for mining and industrial work environments and must be monitored. We provide theoretical analysis of real-time measurements for determining RCS mass concentration without the use of filters by using photoacoustic spectroscopy. The suspended dust in the mine air can be continuously sampled by the photoacoustic instrument. A tunable quantum cascade laser is the light source, allowing for determination of interferences such as kaolinite, coal dust, and water vapor. The most useful spectral region is found to be between 11 and 13 μm. Absorption by water vapor, and, to a lesser extent, carbon dioxide, in this spectral region has gaps that allow for quantification of the aforementioned dust species as well as a convenient check on the calibration of the instrument. This work brings photoacoustic measurement of aerosol to the mid infrared range where spectrally dependent light absorption can be used to quantify dust composition and mass concentration.

Black carbon (BC), carbon monoxide (CO), and carbon dioxide (CO2) were measured in Mexico City (UNAM observatory) with a Photoacoustic Extinctiometer-PAX (BC) and a Cavity Ring-Down Spectroscopy analyzer-CRDS (CO and CO2), from November 2014 to July 2016. The objective of this study was to determine temporal variations of BC, CO, and CO2, their mutual correlations, and evaluation of the Mexico City emission inventory. The highest concentrations of pollutants were detected in cold dry season. The average concentrations of BC, CO, and CO2, for the entire period, were 2.95 mu g m(-3), 0.64 ppm, and 421.81 ppm, respectively. We calculated Delta BC/Delta CO, Delta BC/Delta CO2, and Delta CO/Delta CO2 using three methods to obtain a confidence interval for the emission ratios. BC, CO, CO2 concentrations, and the Delta BC/Delta CO ratio were maximum in the early morning, while the Delta BC/Delta CO2 and Delta CO/Delta CO2 peak was maximum in the afternoon. BC and CO have a weekday/weekend difference. The estimated slopes (Delta BC/Delta CO, Delta BC/Delta CO2, and Delta CO/Delta CO2) were compared with the emission ratios (BC/CO, BC/CO2, and CO/CO2) derived of the 2016 Mexico City emissions inventory. For mobile sources, the emission ratios of BC/CO and BC/CO2 were within the measurement range of Delta BC/Delta CO and Delta BC/Delta CO2, while CO/CO2 was under-estimated in the emission inventory.

Deriving aerosol optical depth (AOD) from space-borne observations is still challenging due to uncertainties associated with sensor calibration drift, cloud screening, aerosol type classification, and surface reflectance characterization. As an initial step to understanding the physical processes impacting these uncertainties in satellite AOD retrievals, this study outlines a theoretical approach to estimate biases in the satellite aerosol retrieval algorithm affected by surface albedo and prescribed aerosol optical properties using a simplified radiative transfer model with a traditional error propagation approach. We expand the critical surface reflectance concept to obtain the critical surface albedo (CSA), critical single scattering albedo (CSSA), and critical asymmetry parameter (CAP). The top-of-atmosphere (TOA) reflectance is not sensitive to significant variability in aerosol loading (AOD) at the critical value; thus, the AOD cannot be determined. Results show that 5% bias in surface albedo (A), single scattering albedo (SSA), or asymmetry parameter (g) lead to large retrieved AOD errors, especially high under conditions when A, SSA, or g are close to their critical values. The results can be useful for future research related to improvements of satellite aerosol retrieval algorithms and provide a preliminary framework to analytically quantify AOD uncertainties from satellite retrievals.

Cheatgrass (Bromus Tectorum) is a highly invasive species in the Great Basin of the Western USA that is increasing the frequency and intensity of wildland fires. Though cheatgrass plays a significant role in the fire ecology of the Great Basin, very little is known about its combustion emissions. The fresh smoke from 16 open laboratory burns of cheatgrass was analyzed using real-time measurements and filter analysis. We presented measured intensive optical properties of the emitted smoke, including absorption Ångström exponent (AAE), scattering Ångström exponent (SAE), single scattering albedo (SSA), and other combustion properties, such as modified combustion efficiency (MCE) and fuel-based emission factors (EFs). In addition, we gave a detailed chemical analysis of polar organic species in cheatgrass combustion emissions. We presented EFs that showed a large variation between fuels and demonstrated that analysis of combustion emissions for specific fuels was important for studying and modeling the chemistry of biomass-burning emissions.

En Juriquilla-Querétaro, se midió la concentración en masa de carbono negro (BC), la relación de mezcla de monóxido de carbono (CO) y el dióxido de carbono (CO2). Las mediciones se realizaron del 01 de marzo al 30 de abril de 2016. En abril, los valores medios del BC (1.23 µg/m3) y CO (0.30 ppm) fueron mayores a sus correspondientes del mes de marzo (1.08 µg/m3 y 0.26 ppm, respetivamente). El CO2 no sufrió variación en estos meses y mantuvo un valor casi constante de alrededor de 406 ppm. Las tendencias diarias del BC, CO y CO2 fueron similares, con un máximo pronunciado por la mañana y un mínimo por la tarde. Estos contaminantes alcanzaron su valor máximo alrededor de las 08:00-09:00 Hora Local (HL). Se presentó una buena correlación en el ajuste lineal de BC-CO, BC-CO2 y CO-CO2, lo que sugiere que estos contaminantes provendrían de las mismas fuentes. Se observó un efecto fin de semana (valores más bajos del BC, CO y CO2 el fin de semana en comparación con los de días laborables), principalmente en las horas de máximo tráfico.Al no existir estudios de mediciones continuas de BC, CO y CO2; desarrollamos esta investigación para determinar las tendencias diarias de estos contaminantes y sus correlaciones mutuas en una zona periurbana, en Querétaro.

Fire detection faces challenges of increasing sensitivity, accuracy, and response speed while reducing false alarms. Air quality sensors measure fire emission signatures similar to smoke detectors but are often more sensitive. Recent advancement in air quality sensors provides an opportunity to improve fire detection. This study used low-cost and research-grade gas and particle sensors to detect and characterize emissions from laboratory smoldering and flaming tests of three spacecraft-relevant materials. The electrochemical carbon monoxide (CO) sensor sensitively detected fire emissions in all but a pyrolysis test, whereas the metal oxide volatile organic compound (VOC) sensor with cross sensitivity for CO detected fire emissions in all tested cases. Several low-cost particle sensors, although saturated at high concentrations, detected smoke at low concentrations. A combination of CO/VOC and particle sensors would provide sensitive fire detection distinct from non-combustion nuisance sources. In support of the ongoing Spacecraft Fire Safety Experiments (Saffire), the DustTrak DRX aerosol monitor was evaluated for smoke measurement. It measured particle concentrations over a wide range and its single particle counting provided additional size distribution data similar to that of an optical particle counter. However, the single particle counting accuracy degraded at high concentrations due to coincidence errors.

In Juriquilla-Queretaro, the mass concentration of black carbon (BC), the mixing ratio of carbon monoxide (CO) and carbon dioxide (CO2) were measured. Measurements were made from March 1 to April 30, 2016. In April, the mean values of BC (1.23 μg / m3) and CO (0.30 ppm) were higher than their corresponding values for March (1.08 μg / m3 and 0.26 ppm, respectively). CO2 did not variate in these months and maintains almost a stabilized value around 406 ppm. The daily trends of BC, CO, and CO2 were similar with a pronounced maximum in the morning and a minimum in the afternoon. These pollutants reach a high level around 08:00-09:00 Local Time (LT). A good correlation was estimated in the linear regression of BC-CO, BCCO2, and COCO2, suggesting that these pollutants proceed from the same sources. A weekend effect (lower values of BC, CO, and CO2 on the weekend compared to working days) was mainly observed during rush-hour traffic. As there are no studies of continuous measurements of BC, CO, and CO2, this research was conducted to determine the daily trends of these pollutants and their mutual correlations in a peri-urban area of Queretaro. Palabras clave: Carbono negro, dióxido de carbono, efecto fin de semana, monóxido de carbono. En Juriquilla-Querétaro, se midió la concentración en masa de carbono negro (BC), la relación de mezcla de monóxido de carbono (CO) y el dióxido de carbono (CO ). Las mediciones se realizaron del 01 de marzo al 30 de abril de 2016. En 2 3 abril, los valores medios del BC (1.23 μg/m ) y CO (0.30 ppm) fueron mayores a sus correspondientes del mes de marzo 3 (1.08 μg/m y 0.26 ppm, respetivamente). El CO no sufrió variación en estos meses y mantuvo un valor casi constante de 2 alrededor de 406 ppm. Las tendencias diarias del BC, CO y CO fueron similares, con un máximo pronunciado por la 2 mañana y un mínimo por la tarde. Estos contaminantes alcanzaron su valor máximo alrededor de las 08:00-09:00 Hora Local (HL). Se presentó una buena correlación en el ajuste lineal de BC-CO, BC-CO y CO-CO , lo que sugiere que 2 2 estos contaminantes provendrían de las mismas fuentes. Se observó un efecto fin de semana (valores más bajos del BC, CO y CO el fin de semana en comparación con los de días laborables), principalmente en las horas de máximo tráfico. Al 2 no existir estudios de mediciones continuas de BC, CO y CO ; desarrollamos esta investigación para determinar las 2 tendencias diarias de estos contaminantes y sus correlaciones mutuas en una zona periurbana, en Querétaro. RESUMEN

Conventional spacecraft smoke detectors are not optimized for detecting space smoke, which differs from that on Earth due to the fuel materials, burning conditions, particle formation/transformation processes, and lack of gravity. More effective smoke detectors can be developed with knowledge of smoke chemical compositions, size distributions, optical properties, and emission factors specific to spacecraft-relevant materials, e.g., Poly(methyl methacrylate) (PMMA), cotton, and Nomex® fabric. In normal gravity testing it is found that carbon is the main smoke component, with elemental carbon constituting ∼90% of particle mass for flaming PMMA combustion and organic matter constituting ≳80% of particle mass for other fuels and test conditions. Particles emitted from flaming PMMA are fractal-like soot agglomerates, different from the near spherical particles found for other fuels and burning conditions. Particle size distributions vary during the combustion process. When particle concentrations are near maximum, smoldering cotton generates bimodal number size distributions, while other fuels and test conditions exhibit unimodal lognormal number size distributions. Smoke particles from flaming PMMA combustion are black with single scattering albedos <0.3, while particles from other burned materials demonstrate low light absorption, with single scattering albedos >0.9 at 405–781 nm. Mass extinction coefficients are 7.8 m2/g for flaming PMMA and 2.7–4.2 m2/g for smoldering combustions at 632.8 nm. CO and PM2.5 emission factors are higher for smoldering than for flaming combustions, while CO2 emission factors are higher for flaming combustions.