Face-to-face with scorching wildfire: potential toxicant exposure and the health risks of smoke for wildland firefighters at the wildland-urban interface.

As wildfire risks have elevated due to climate change, the health risks that toxicants from fire smoke pose to wildland firefighters have been exacerbated. Recently, the International Agency for Research on Cancer (IARC) has reclassified wildland firefighters' occupational exposure as carcinogenic to humans (Group 1). Wildfire smoke contributes to an increased risk of cancer and cardiovascular disease, yet wildland firefighters have inadequate respiratory protection. The economic cost of wildland fires has risen concurrently, as illustrated by the appropriation of $45 billion for wildfire management over FYs 2011-2020 by the U.S. Congress. Occupational epidemiological studies of wildland firefighters are crucial for minimizing health risks; however, they must account for the mixture of exposures in wildfire smoke. This review focuses on four aspects of wildland firefighters' health risks at the wildland-urban interface: 1) economic costs and health impact, 2) respiratory protection, 3) multipollutant mixtures, and 4) proactive management of wildfires.

Evaluation of Mass Spectrometric Methods for Screening Polycyclic Aromatic Hydrocarbons in the Particulate Phase of Wildfire/Biomass Smoke.

Polycyclic aromatic hydrocarbons (PAHs) are a class of compounds containing multiple aromatic rings formed during incomplete combustion. Since many of them are known mutagens and carcinogens, PAHs found in the particulate matter (PM) from the wildfire smoke may pose significant health risks to the wildland firefighters. It is pivotal to determine the levels of PAHs in the PM to evaluate the health effects of their inhalation exposure. However, the determination of PAHs using the conventional chromatographic approaches is often time-consuming and laborious. Herein, we describe a novel method for screening nonpolar and polar PAHs in the PM of smoke by direct analysis in real-time mass spectrometry (DART-MS). PM2.5 and PM10 samples were collected on the quartz filters with a sampling system consisting of a cascade impactor with a portable sampling pump. Various indoor and outdoor experiments from biomass burns were conducted to evaluate the PM sampling systems. PAHs were analyzed by DART-MS and gas chromatography-mass spectrometry (GC-MS) methods. The PM samples were collected in California during the wildfire season of fall 2020, and significant levels of multiple nonpolar PAHs and polar PAHs were detected. Overall, the DART-MS method has shown promising ability for high-throughput screening of PAHs in the PM of smoke. Further studies are currently under way to apply this method to study the particulate phase PAH exposures of wildland firefighters during their firefighting activities.

Kinetics Study of the Reactions of 4-Methyl-2-Pentanone and m-Ethyl Toluene with Hydroxyl Radicals between 240 and 340 K and 1-8 Torr Using the Relative Rate/Discharge Flow/Mass Spectrometry Technique.

The kinetics of reactions of 4-methyl-2-pentanone (MIBK) and m-ethyl toluene (MET) with hydroxyl radicals has been studied at a total pressure of 1-8 Torr and 240-340 K using the RR/DF/MS technique. The rate constant for the reaction of MIBK with the hydroxyl radical was found to be essentially pressure-independent in the range of 1-3 Torr. The rate constant for MET reaction with the hydroxyl radical increased with pressure at 1-5 Torr, and a high pressure limit was reached at 5 Torr. At 298 K, rate constants (in cm3 molecule-1 s-1) of kMIBK+OH(298 K) = (1.25 ± 0.21) × 10-11 and kMET+OH(298 K) = (2.05 ± 0.23) × 10-11 were determined with n-nonane as the reference compound, while kMIBK+OH(298 K) = (1.25 ± 0.11) × 10-11 and kMET+OH(298 K) = (1.88 ± 0.17) × 10-11 were obtained with 1,4-dioxane as the reference compound, where kMIBK+OH was measured at 1 Torr and kMET+OH was measured at 5 Torr. The rate constant of MIBK reaction with the hydroxyl radical was found to be negatively dependent on temperature at 240-340 K, with an Arrhenius expression of kMIBK+OH(T) = (2.00 ± 0.07) × 10-12 exp[(535 ± 11)/T] cm3 molecule-1 s-1. The rate constant of MET reaction with the hydroxyl radicals was also found to negatively depend on temperature at 240-340 K but with nonlinear behavior in the Arrhenius plot.

Kinetics Study of the Reactions of OH with n-Undecane and n-Dodecane Using the RR/DF/MS Technique.

The kinetics of the reactions of hydroxyl radical with n-undecane (n-C11H24) and n-dodecane (n-C12H26) has been studied at 240-340 K and a total pressure of 1 Torr using the relative rate/discharge flow/mass spectrometry (RR/DF/MS) technique. The rate constants at 298 K for these reactions were determined to be kn-undecane+OH = (1.59 ± 0.24) × 10-11 cm3 molecule-1 s-1 and kn-dodecane+OH = (1.83 ± 0.26) × 10-11 cm3 molecule-1 s-1, respectively. The rate constants of these reactions were found to positively dependent on temperature at 277-340 K, and negatively dependent on temperature at 240-277 K. The atmospheric lifetime of these compounds are estimated to be 25.8 and 19.8 h for n-undecane and n-dodecane, respectively, based the kinetics results in the present study.

Kinetic and dynamic investigations of OH reaction with styrene.

The kinetics of hydroxyl radical reaction with styrene has been studied at 240-340 K and a total pressure of 1-3 Torr using the relative rate/discharge flow/mass spectrometry technique. In addition, the dynamics of the reaction was also studied using the ab initio molecular orbital method. The reaction was found to be essentially pressure independent over 1-3 Torr at both 298 and 340 K. At 298 K, the average rate constant was determined, using four different reference compounds, to be kstyrene+OH = (5.80 ± 0.49) × 10(-11) cm(3) molecule(-1) s(-1). At 240-340 K, the rate constant of this reaction was found to be negatively dependent on temperature with an Arrhenius expression determined to be kstyrene+OH = (1.02 ± 0.10) × 10(-11) exp[(532 ± 28)/T] cm(3) molecule(-1) s(-1). Observation of mass spectral evidence of adduct products and their respective fragment ions suggests that the reaction proceeds with addition of the OH to the vinyl carbons of the styrene molecule. Ab initio calculations of both the addition and the abstraction pathways predict that the addition pathways are more energetically favorable because of large exothermicity and essentially barrierless transition state associated with the additions, which is consistent with the experimental observations. Using the styrene + OH rate constant determined at 277 K in the present work, the atmospheric lifetime of styrene was estimated to be 4.9 h.

Kinetics study of the reaction of OH radicals with C5-C8 cycloalkanes at 240-340 K using the relative rate/discharge flow/mass spectrometry technique.

Rate constants of reactions of hydroxyl radical with cyclopentane (k1), cyclohexane (k2), cycloheptane (k3), and cyclooctane (k4) have been acquired at 240-340 K and a total pressure of about 1 Torr using the technique of relative rate combined with discharge flow and mass spectrometry (RR/DF/MS). At 298 K, the rate constants are determined using two reference compounds, which are averaged to be k1 = (4.81 ± 0.88) × 10(-12), k2 = (6.41 ± 0.85) × 10(-12), k3 = (10.30 ± 1.44) × 10(-12), and k4 = (1.42 ± 0.27) × 10(-11) cm(3) molecule(-1) s(-1). The Arrhenius expressions at 240-340 K for these reactions are determined to be k1(T) = (2.43 ± 0.50) × 10(-11)exp[-(481 ± 58)/T], k2(T) = (3.96 ± 0.60) × 10(-11)exp[-554 ± 42)/T], k3(T) = (5.74 ± 0.66) × 10(-11)exp[-527 ± 33)/T], and k4(T) = (1.12 ± 0.21) × 10(-10)exp[-626 ± 53)/T]. Using the kcycloalkane+OH(277 K) values measured in the present work, the atmospheric lifetime for cyclopentane, cyclohexane, cycloheptane, and cyclooctane is estimated to be about 78, 64, 38, and 29 h, respectively.

Kinetics study of reactions of α-pinene and ß-pinene with hydroxyl radical at 1-8 Torr and 240-340 K using the relative rate/discharge flow/mass spectrometry method.

The kinetics of reactions of α-pinene and ß-pinene with hydroxyl radicals (OH) has been investigated at 1-8 Torr and 240-340 K using the relative rate/discharge flow/mass spectrometry (RR/DF/MS) technique. Our kinetic results indicate that at 298 K the rate constant of the reactions of α-pinene and ß-pinene with hydroxyl radicals has little pressure dependence over the 1-8 Torr pressure range, suggesting that the high pressure limit of these reactions has been reached at 1 Torr. The rate constant of these reactions was found to negatively depend on the temperature at 240-340 K, which is consistent with previous investigations using different techniques. The Arrhenius equation for α-pinene and ß-pinene with hydroxyl radical was determined to be k(α-pinene) = (1.21 ± 0.20) × 10(-11)exp[(441 ± 46)/T] cm(3) molecule(-1) s(-1) and k(ß-pinene) = (1.65 ± 0.10) × 10(-11)exp[(470 ± 17)/T] cm(3) molecule(-1) s(-1), respectively. Using the rate constant determined at 277 K in this work and the average global hydroxyl radical concentration, the atmospheric lifetime of α-pinene and ß-pinene was estimated to be 5.8 and 3.8 h, respectively.

Experimental and theoretical investigation of homogeneous gaseous reaction of CO2(g) + nH2O(g) + nNH3(g) → products (n = 1, 2).

Decreasing CO2 emissions into the atmosphere is key for reducing global warming. To facilitate the CO2 emission reduction efforts, our laboratory conducted experimental and theoretical investigations of the homogeneous gaseous reaction of CO2(g) + nH2O(g) + nNH3(g) → (NH4)HCO3(s)/(NH4)2CO3(s) (n = 1 and 2) using Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy and ab initio molecular orbital theory. Our FTIR-ATR experimental results indicate that (NH4)2CO3(s) and (NH4)HCO3(s) are formed as aerosol particulate matter when carbon dioxide reacts with ammonia and water in the gaseous phase at room temperature. Ab initio study of this chemical system suggested that the reaction may proceed through formation of NH3·H2O(g), NH3·CO2(g), and CO2·H2O(g) complexes. Subsequent complexes, NH3·H2O·CO2 and (NH3)2·H2O·CO2, can be formed by adding gaseous reactants to the NH3·H2O(g), NH3·CO2(g), and CO2·H2O(g) complexes, respectively. The NH3·H2O·CO2 and (NH3)2·H2O·CO2 complexes can then be rearranged to produce (NH4)HCO3 and (NH4)2CO3 as final products via a transition state, and the NH3 molecule acts as a medium accepting and donating hydrogen atoms in the rearrangement process. Our computational results also reveal that the presence of an additional water molecule can reduce the activation energy of the rearrangement process. The high activation energy predicted in the present work suggests that the reaction is kinetically not favored, and our experimental observation of (NH4)HCO3(s) and (NH4)2CO3(s) may be attributed to the high concentrations of reactants increasing the reaction rate of the title reactions in the reactor.

Inhibition of Mas G-protein signaling improves coronary blood flow, reduces myocardial infarct size, and provides long-term cardioprotection.

The Mas receptor is a class I G-protein-coupled receptor that is expressed in brain, testis, heart, and kidney. The intracellular signaling pathways activated downstream of Mas are still largely unknown. In the present study, we examined the expression pattern and signaling of Mas in the heart and assessed the participation of Mas in cardiac ischemia-reperfusion injury. Mas mRNA and protein were present in all chambers of human hearts, with cardiomyocytes and coronary arteries being sites of enriched expression. Expression of Mas in either HEK293 cells or cardiac myocytes resulted in constitutive coupling to the G(q) protein, which in turn activated phospholipase C and caused inositol phosphate accumulation. To generate chemical tools for use in probing the function of Mas, we performed a library screen and chemistry optimization program to identify potent and selective nonpeptide agonists and inverse agonists. Mas agonists activated G(q) signaling in a dose-dependent manner and reduced coronary blood flow in isolated mouse and rat hearts. Conversely, treatment of isolated rat hearts with Mas inverse agonists improved coronary flow, reduced arrhythmias, and provided cardioprotection from ischemia-reperfusion injury, an effect that was due, at least in part, to decreased cardiomyocyte apoptosis. Participation of Mas in ischemia-reperfusion injury was confirmed in Mas knockout mice, which had reduced infarct size relative to mice with normal Mas expression. These results suggest that activation of Mas during myocardial infarction contributes to ischemia-reperfusion injury and further suggest that inhibition of Mas-G(q) signaling may provide a new therapeutic strategy directed at cardioprotection.

Detection and quantification of trace organic contaminants in water using the FT-IR-attenuated total reflectance technique.

The Fourier transform infrared-attenuated total reflectance (FT-IR-ATR) technique has been used to detect and quantify the following volatile organic compounds (VOCs) in water: 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, styrene, and tetrachloroethylene, among which the first three compounds were investigated at parts per million levels for the first time. Enhancement of the detection was made by (1) coating the ATR crystal with a hydrophobic polymer membrane, (2) optimizing the flow rate of the sample solution, (3) varying polymer membrane thickness, and (4) increasing the number of reflection bounces within the ATR crystal. Our flow rate optimization confirmed a previous finding that turbulent flow is more favorable than laminar flow in detecting the VOCs in water. However, decreases of ATR signal intensity were observed at very high turbulency due to analytes flowing too quickly through and exiting the ATR cell to be adsorbed onto the polymer membrane. The optimal membrane thickness was found to be associated with the maximum overlap between the IR evanescent wave penetration depth and the analyte diffusion depth. Consequently, there is no universal optimal flow rate and optimal polymer membrane thickness for detection of all VOCs. Doubling the number of IR reflection bounces within the ATR crystal enhanced both detection and sensitivity by about a factor of 2. Finally, it was observed that the detection limit concentrations decrease with the water solubility of the VOCs.

A kinetic study of the reaction of OH with xylenes using the relative rate/discharge flow/mass spectrometry technique.

A kinetics study for the reaction of OH with o-, m-, and p-xylene has been conducted at 1-10 Torr and 240-340 K using the relative rate/discharge flow/mass spectrometry technique with 1,4-dioxane as the reference compound. At 298 K, the rate constants for the reaction of OH with all three isomers of xylene exhibited prominent positive pressure dependence up to 5 Torr, and the reactions reached a high-pressure limit at 8 Torr, with a high pressure limit rate constant of k(o-xylene) = (1.19 +/- 0.07) x 10(-11) cm(3) molecule(-1) s(-1), k(m-xylene) = (2.14 +/- 0.14) x 10(-11) cm(3) molecule(-1) s(-1), and k(p-xylene) = (1.19 +/- 0.07) x 10(-11) cm(3) molecule(-1) s(-1), respectively, which are in good agreement with literature values. The results of the temperature-dependence study indicated that, in all three reactions, there is negative temperature dependence at temperatures greater than 298 K. The reaction of OH with xylene may proceed with addition of the OH radical to the benzene ring at room temperature and below, with an equilibrium established between the reactants and the xylene-OH adduct. At 298-340 K, the equilibrium is shifted toward the reactants, giving rise to a negative temperature dependence of the rate constant, and this may also associate with a transition of the reaction from the addition mechanism to the abstraction mechanism. On the basis of our kinetic results at 277 K, the atmospheric lifetimes of o-, m-, and p-xylene are estimated to be about 29, 14, and 31 h, respectively.

FTIR and Ab initio investigations of the MTBE-water complex.

The infrared spectrum of methyl tert-butyl ether (MTBE) in liquid water has been studied using both FTIR absorption and FTIR-ATR spectroscopy in conjunction with ab initio calculations. Compared to the liquid MTBE IR spectrum, the C-O and C-C stretching vibrational frequencies of MTBE in water are found to shift to the red and blue by up to 26 and 9 cm (-1), respectively. Ab initio calculations suggest that these shifts are caused by complexation of the MTBE molecule with water molecules through hydrogen bonding. Our observation of the vibrational frequency shifts in the IR spectrum of MTBE in water provides the IR spectroscopic evidence of organics-water complexes in the diluted aqueous solution. The implication of the effect of the hydrogen bond in organics-water complexation on solvation and reactivity of the organic compound in aqueous chemical processes is discussed.

Kinetics Investigation of OH reaction with isoprene at 240-340 K and 1-3 torr using the relative rate/discharge flow/mass spectrometry technique.

The kinetics of the reaction of OH radical with isoprene has been investigated at a total pressure of 1-3 Torr over a temperature range of 240-340 K using the relative rate/discharge flow/mass spectrometry (RR/DF/MS) technique. The reaction of isoprene with OH was found to be independent of pressure over the pressure range of 1-3 Torr at 298 K, and the reaction had reached its high-pressure limit at 1 Torr. However, the rate constant of this reaction is found to positively depend on pressure at 1-3 Torr and 340 K. At 298 K, the rate constant of this reaction was determined to be k1 = (10.4 +/- 1.9) x 10(-11) cm3 molecule(-1) s(-1), which is in good agreement with literature values. The Arrhenius expression for this reaction was determined to be k1 = (2.33 +/- 0.09) x 10(-11) exp[(444 +/- 27)/T] cm3 molecule(-1) s(-1) at 240-340 K. The atmospheric lifetime of isoprene was estimated to be 2.9 h based on the rate constant of isoprene + OH determined at 277 K in the present work.

Sphingosine 1-phosphate S1P2 and S1P3 receptor-mediated Akt activation protects against in vivo myocardial ischemia-reperfusion injury.

Sphingosine 1-phosphate (S1P) is released at sites of tissue injury and effects cellular responses through activation of G protein-coupled receptors. The role of S1P in regulating cardiomyocyte survival following in vivo myocardial ischemia-reperfusion (I/R) injury was examined by using mice in which specific S1P receptor subtypes were deleted. Mice lacking either S1P(2) or S1P(3) receptors and subjected to 1-h coronary occlusion followed by 2 h of reperfusion developed infarcts equivalent to those of wild-type (WT) mice. However, in S1P(2,3) receptor double-knockout mice, infarct size following I/R was increased by >50%. I/R leads to activation of ERK, JNK, and p38 MAP kinases; however, these responses were not diminished in S1P(2,3) receptor knockout compared with WT mice. In contrast, activation of Akt in response to I/R was markedly attenuated in S1P(2,3) receptor knockout mouse hearts. Neither S1P(2) nor S1P(3) receptor deletion alone impaired I/R-induced Akt activation, which suggests redundant signaling through these receptors and is consistent with the finding that deletion of either receptor alone did not increase I/R injury. The involvement of cardiomyocytes in S1P(2) and S1P(3) receptor mediated activation of Akt was tested by using cells from WT and S1P receptor knockout hearts. Akt was activated by S1P, and this was modestly diminished in cardiomyocytes from S1P(2) or S1P(3) receptor knockout mice and completely abolished in the S1P(2,3) receptor double-knockout myocytes. Our data demonstrate that activation of S1P(2) and S1P(3) receptors plays a significant role in protecting cardiomyocytes from I/R damage in vivo and implicate the release of S1P and receptor-mediated Akt activation in this process.

Kinetics study of OH radical reactions with n-octane, n-nonane, and n-decane at 240-340 K using the relative rate/discharge flow/mass spectrometry technique.

The kinetics of the reactions of hydroxyl radical with n-octane (k1), n-nonane (k2), and n-decane (k3) at 240-340 K and a total pressure of approximately 1 Torr has been studied using relative rate combined with discharge flow and mass spectrometer (RR/DF/MS) technique. The rate constant for these reactions was found to be positively dependent on temperature, with an Arrhenius expression of k1 = (2.27 +/- 0.21) x 10(-11)exp[(-296 +/- 27)/T], k2 = (4.35 +/- 0.49) x 10(-11)exp[(-411 +/- 32)/T], and k3 = (2.26 +/- 0.28) x 10(-11)exp[(-160 +/- 36)/T] cm3 molecule(-1) s(-1) (uncertainties taken as 2sigma), respectively. Our results are in good agreement with previous studies at and above room temperature using different techniques. Assuming that the reaction of alkane with hydroxyl radical is the predominant form for loss of these alkanes in the troposphere, the atmospheric lifetime for n-octane, n-nonane, and n-decane is estimated to be about 43, 35, and 28 h, respectively.

Experimental and theoretical study of reaction of OH with 1,3-butadiene.

The kinetics of the reaction of hydroxyl radical with 1,3-butadiene at 240-340 K and a total pressure of approximately 1 Torr has been studied using relative rate combined with the discharge flow and mass spectrometer technique. The reaction dynamics of the same reaction has also been investigated using ab initio molecular orbital theory. The rate constant for this reaction was found to be negatively dependent on temperature, with an Arrhenius expression of k1 = (1.58 +/- 0.07) x 10(-11) exp[(436 +/- 13)/T] cm3 molecule(-1) s(-1) (uncertainties taken as 2sigma), which was in good agreement with that reported by Atkinson et al. and Liu et al. at 299-424 K. Mass spectral evidences were found for the addition of OH to both the terminal and the internal carbons of 1,3-butadiene. Our computational results suggest that both addition of OH to 1,3-butadiene and the abstraction of hydrogen atom from 1,3-butadiene by the OH radical are exothermic processes and that the addition of OH to the terminal carbon of the 1,3-butadiene is predicted to have an activation energy of 0.7 kcal mol(-1), being the most energetically favored reaction pathway.

Tissue remodeling of rat pulmonary arteries in recovery from hypoxic hypertension.

The reversibility of tissue remodeling is of general interest to medicine. Pulmonary arterial tissue remodeling during hypertension induced by hypoxic breathing is well known, but little has been said about the recovery of the arterial wall when the blood pressure is lowered again. We hypothesize that tissue recovery is a function of the oxygen concentration, blood pressure, location on the vascular tree, and time. We measured the changes of blood pressure, vessel lumen, vessel wall thicknesses, and opening angle of each segment of the blood vessel at its zero-stress state after step changes of the oxygen concentration in the breathing gas. The zero-stress state of each vessel is emphasized because it is important to the analysis of stress and strain and in morphometry. Experimental results are presented as histories of tissue parameters after step changes of the oxygen level. Tissue characteristics are examined under the hypothesis that they are linearly related to changes in the local blood pressure. Under this linearity hypothesis, each aspect of the tissue change can be expressed as a convolution integral of the blood pressure history with a kernel called the indicial response function. It is shown the indicial response function for rising blood pressure is different from that for falling blood pressure. This difference represents a major nonlinearity of the tissue remodeling process of the blood vessels.

Changes of zero-bending-moment states and structures of rat arteries in response to a step lowering of the blood pressure.

There are many papers on tissue remodeling of blood vessels in hypertension, but there are few documents describing the tissue remodeling of the blood vessels following a step lowering of the blood pressure. The present article presents data on the opening angle, the vessel wall thickness, and the thicknesses of the intima-media and adventitia layers of the blood vessels of the lower body (the abdominal aorta, and the common iliac, femoral, saphenous branch, medial plantar, and plantar metatarsal arteries) of the rat after a step lowering of the blood pressure and flow by a controlled constriction of the aorta below both renal arteries. We found a pattern of changes that depend on space (location on the vascular tree), time (after the blood pressure change), and the intensity of disturbance. We model mathematically the dynamics shown by the experimental results by means of the indicial response functions, which are defined as the morphometric changes in response to a step decrease of blood pressure or blood flow. Under the hypothesis that there is a range of linearity between the degree of tissue remodeling and the amplitude of the pressure change, we can use the indicial functions to predict the remodeling of the vessel under an arbitrary history of decreasing blood pressure; and conversely, we can compute the indicial response functions from pertinent results of a single experiment. The totality of all our experiments is consistent with the linearity hypothesis within the range of the experiment. The mathematical analysis and the formulas are presented in the Appendix.