North Pole, Alaska, experiences severe wintertime air quality degradation driven by elevated residential biomass burning and persistent meteorological inversions. However, the comprehensive characterization and underlying drivers of fine particulate matter (PM2.5) in this region remain understudied. This study integrates data from four consecutive winter campaigns, combining pollutant measurements and meteorological variables to assess the key drivers of the PM2.5 and its carbonaceous components. Major factors influencing the PM2.5 threshold exceedances were identified using generalized ordered logit regression (GOLR) with an overall accuracy of 67.51 %. Colder temperatures, low absolute pressure, higher relative humidity (RH), elevated Absorption & Aring;ngstr & ouml;m Exponent (AAE), and zonal component of wind (east to west wind direction), fireworks, and specific temporal patterns (afternoon, evening, and night hours), along with their interactions, were associated with higher PM2.5 levels (>55.4 mu g/m(3)). Mean organic carbon to black carbon ratios (OC/BC) ranged from 8.25 to 10.83 across the four campaigns, consistent with influence from both biomass burning and secondary organic aerosol (SOA) formation. High mean and median OC/BC ratios, strong correlations (R-2 = 0.73-0.97) between PM2.5 and total carbon (TC), and weak to strong correlations (R-2 = 0.47-0.87) between PM2.5 and black carbon (BC), highlighted source influence and atmospheric processing. The larger variability in OC/BC, ranging from 0.84 to 70.95, indicates the mixing of different primary sources and considerable SOA formation or atmospheric aging. Inter-winter variability in PM2.5 concentrations was primarily driven by local emissions, meteorological conditions including temperature, winds, and planetary boundary layer height (PBLH), and pollutant dispersion patterns, with minimal influence from long-range transport. AAE consistently showed positive associations with elevated PM2.5 levels, indicating biomass burning was an important source during the campaigns.

Volatile chemical products (VCPs), including organic species emitted from pesticides, coatings, cleaning products, and personal care products, account for more than half of the urban VOC emissions in major North American and European cities. However, VCP emissions, spatial and temporal distributions, and impacts vary widely. Despite being the fourth largest U.S. city, Houston, Texas, lacks measured VCP concentration and emission data. This study presents the first spatial and temporal measurements of selected VCP tracers in Houston, Texas, using a Vocus 2R Chemical Ionization Mass Spectrometer on a mobile platform. Ambient measurements of five major VCP tracers, including D5-siloxane, monoterpenes, para-dichlorobenzene, para-chlorobenzotrifluoride (PCBTF), and 2,2,4-trimethyl-1,3-pentanediol isobutyrate (Texanol), were collected in winter and summer 2023. Several compounds exhibited significantly higher averaged concentrations, with pronounced spatial and seasonal variability, distinguishing Houston from urban areas in the temperate and cooler climate zone. A customized box model was employed to estimate seasonal emissions for the Greater Houston Area, showing that emissions of most VCPs were significantly higher during the summer. This study provides critical insights into the distribution and emission of VCPs in a subtropical metropolitan area, advancing methods for assessing VCP emissions and concentrations across cities and improving understandings of their impacts on air quality, climate, and public health.

Volatile chemical products (VCPs) in urban environments account for a significant portion of the volatile organic compounds (VOCs), enhancing the production of tropospheric ozone and secondary organic aerosols. Residential areas are an important source of VCPs in the urban environment, though few studies have examined the emission of VCPs in metropolitan areas from subtropical regions. To bridge the knowledge gap, this study aims to analyze the concentration and emission of D5-siloxane, a compound typically served as a tracer to characterize VCP emission from residential areas. The Texas A&M mobile laboratory, equipped with a Vocus 2R Chemical Ionization Mass Spectrometer (CIMS), and other gas and particle analyzers, continuously sampled the ambient gas phase concentration of D5-siloxane during a field deployment in a residential neighborhood near Houston, TX. A 0-D box model combining Planetary Boundary Layer Height (PBL) height, hourly D5-siloxane concentration, gas deposition velocities, and D5-siloxane reaction rate with hydroxyl radicals was constructed to represent emissions during our sampling period to derive the emission intensities of D5-siloxane. Monte Carlo statistical analysis was performed to gain insights into the emission profile of D5-siloxane, showing higher emission rates compared with other cities in North America but comparable to emissions of European cities. This study presents time-series concentrations and emissions of D5-siloxane in a subtropical residential area during the wintertime. The findings illustrate the temporal profile of D5-siloxane in a typical residential neighborhood in the Southeast United States and provide valuable data to enhance model parameterizations.

This study investigated the impacts of the 2023 haze episode on air quality and respiratory health in the Delhi- National Capital Region (Delhi-NCR), India. Monitoring data for PM2.5, PM10, NO2, NH3, SO2, O3, and CO were collected at four representative sites (Delhi, Gurugram, Greater Noida, and Ghaziabad) and analyzed for spatiotemporal variations. Fire hotspot analysis, meteorological data, and backward trajectory analysis modeling revealed the elevated pollution levels during the haze episode were attributable to increased local emissions coupled with the transport of pollutants from biomass burning in neighboring states. To assess health risks, the International Commission on Radiological Protection (ICRP) modeling was used to estimate respiratory deposition dose (RDD) of PM 2.5 and PM10 in the head airway (HA), tracheobronchial (TB), and alveolar (AL) regions for both males and females under three modes of metabolic activities of seated, walking and exercise. The results indicated a substantial increase in the total RDD (sum of HA, TB, and AL regions) across all sites, genders, and activity levels. For instance, PM 2.5 RDD in Delhi increased from 1.03 to 2.44 mu g/min during the haze period for males under seated activity and from 0.72 to 1.69 mu g/min for females. Overall, the study estimated a 130 % increase in health risk during the haze period across all activity levels and genders.

The central goal of this work is to improve our understanding of the distinctive and unusual chemistry of aerosol particles released from firework displays and their potential health risks due to inhalation exposure. The chemical composition of fine particles (PM2.5) released from three commonly used sparklers (low smoke sparklers (LSS), whistling sparklers (WS) and colored sparklers (CS)) was investigated. In particular, total and water soluble elemental fractions (22 elements) and 13 polycyclic aromatic hydrocarbons (PAHs) in PM2.5 were quantified. The particulate emissions from LSS had relatively lower particulate-bound metals and less water-soluble fractions in them compared to those from WS and CS. However, PAHs were found to be relatively higher in LSS compared to those from WS and CS. Health risk due to inhalation of PM2.5 emitted from all the three types of sparklers was estimated for various dilution conditions including the case with little or no dispersion of particles. It was observed that WS had the highest carcinogenic risk (25 × 10 for adults and 75 × 10 6 for children) followed by CS (2.6 × 10 for adults and 7.9 × 10 for children) and LSS (7.6 × 10 for adults and 2.6 × 10 for children) for the worst case scenario of no dilution of emitted particles during inhalation. This carcinogenic risk is pronounced only when there is no or very low dilution (~10) of emitted particles during inhalation. The health risk estimates for all sparkler types are below acceptable limits for dilution factors above 80 and thus exposure to PM2.5 in sparkler emissions is unlikely to have serious health effects. The water soluble fraction of metals (bioavailable metals) made a major contribution to the carcinogenic health risk due to inhalation of PM2.5 released from WS (~100%) and CS (~96%) while PAHs played a major role in the carcinogenic risk associated with PM2.5 from LSS (~66%).

This study has investigated the chemical association among acidic gases, ammonia and secondary inorganic aerosols based on hourly measurements in a tropical urban atmosphere. The 24 hr average concentrations of SO2, NH3, HONO, HNO3 and HCl were 21.77, 2.47, 1.73, 3.00 and 0.08 μg/m3, respectively while those of SO42−, NO3−, Cl−, Na+, K+, NH4+, Ca2+ and Mg2+ in PM2.5 were 4.41, 1.29, 0.28, 0.30, 0.32, 1.76, 0.14 and 0.07 μg/m3, respectively. The results of this study for SO2, NH3, HONO, HCl, SO42− and Cl− showed significant diurnal variations, whereas there was a lack of significant diurnal variations for HNO3, NO3−, Na+, NH4+, Ca2+ and Mg2+. Analysis of the charge balance of ionic species indicated that sufficient NH3 was present most of the time to neutralize both H2SO4 and HNO3 to form (NH4)2SO4 and NH4NO3. The conversion of SO2 into SO42− and HNO3 into NO3− was observed to be sensitive to changes in temperature and relative humidity, respectively. The study area experienced ambient relative humidity, which was higher than the estimated deliquescence relative humidity of NH4NO3 most of the time during the measurement period. As a result, the NH4NO3 formation was thermodynamically favorable during both daytime and nighttime. However, NH4Cl formation was not favored under ammonia-poor conditions. It was observed that biomass burning could trigger nitrate and chloride formation in the ambient air.

The authors regret that inadvertent errors occurred in the estimation of excess lifetime cancer risk (ELCR) in the abovereferenced paper due to an oversight. Specifically, the slope factor of nickel (Ni) we used in the ELCR calculation should have been 8.4 × 10–1 (mg/kg/day)–1 instead of 8.4 × 101 (mg/kg/day)–1. Further, to be consistent with other publications where we assumed the measured chromium (Cr) to exist entirely as hexavalent chromium (Cr(VI)) in airborne particulate matter, we revised the slope factor of Cr to the USEPA recommended value of 42 and recalculated the ELCR accordingly. These revised slope factors do not affect, or influence our overall qualitative conclusion made earlier in the published paper in that whistling sparklers have higher carcinogenic risk compared to low smoke and colored sparklers. The revised ELCR estimates are given below in Tables 2, 3 and 4.

The hybrid systems of steel frames can offer more flexibility and enhance the seismic performance of mid-rise structures. The cold-formed steel (CFS) and hot-rolled steel (HRS) wall system is one such hybrid solution to achieve desired seismic performance level. This study focuses on the numerical analysis of curved steel dampers in the hybrid wall panel (HWP) consisting of cold-formed and hot-rolled squared hollow section (SHS) frames to improve energy dissipation, stiffness, and frame strength during cyclic loading. We evaluated several combinations of damper thicknesses (10 and 13 mm), depths (30, 40, and 50 mm), and angles (30 degrees , 45 degrees , 55 degrees , 60 degrees , 65 degrees , and 75 degrees ) to determine the most efficient damper geometry on seismic performance of the HWP frame. The results show that the energy dissipation, frame strength, and elastic stiffness are optimal when using (a) a 75 degrees damper with 10 mm thickness and 40 mm depth or (b) a 55 degrees damper with 13 mm thickness and 40 mm depth at the top of the hot-rolled section.

A comprehensive year-round field campaign was conducted in the coastal city of Ningbo, China to examine the driving factors of oxidative potential (OP) of PM2.5 and hence its potential health impacts. Using dithiothreitol (DTT) cell-free assay, OP of water-soluble (OPws) and methanol-soluble components (OPmeth) of PM2.5-based samples were measured. Volume-normalised OP (OPvws and OPvmeth) were higher in heating seasons, and mass -normalised OP (OPmws and OPmmeth) peaked in summer. Five sources were identified to be DTT active in OPvws, with road dust (RD) being dominant, while four sources contributed to OPvmeth, with industrial emission (IE) as the largest contributor. Water extracted more toxic components from RD while toxic components in IE and vehicle emission (VE) were more soluble in methanol. We further compared OP values between PM2.5 of similar concentrations and observed that OPvws prevailed in PM2.5 toxicity during clean days (PM2.5 concentration < 38.5 mu g m? 3), while OPvmeth became dominant when PM2.5 concentration was larger than 69.1 mu gm(-3), implying the need to extract whole PM2.5 using both solvents to develop the mitigation strategy for reducing the overall PM2.5 toxicity. Efforts should be devoted to controlling the emissions from dominant sources of both OP in-dicators in specific episode.

Residential areas are being increasingly impacted by wildfire smoke that causes hazardous local ambient air quality conditions. Poor outdoor air quality also exacerbates the quality of indoor air as smoke particles penetrate the building envelope or the heating, ventilation, and air-conditioning (HVAC) filtration systems. In this work, we investigate the impact of wildfire-affected poor ambient air quality on indoor air particulate matter during a wildfire episode in June 2015 in interior Alaska. We measured size-resolved (0.3–10 μm) particle number counts (PNC; numbers/cm3) and calculated particle mass concentrations (PMC; μg/m3) outside and inside of three buildings in Fairbanks, Alaska, during this summer wildfire event. For comparison, the measurements were repeated during a no-wildfire period in summer 2017. Our results show that the fire episode increased the total PNC by factors of 189.4–244 in the outdoor air and by 19.5–150 in the indoor air compared to the total PNC measured during a non-fire season. The PNC was primarily dominated by particles in the size range 0.3–1 μm (> 99%) at all locations during the fire season, whereas the PMC was dominated by particles in the size range from 2.5 to 10 μm (40–67%). The indoor to outdoor ratio (I/O) of PNC during the fire season was significantly lower for an unventilated building (I/O = 0.13 ± 0.001) as compared to those with active (filtered) ventilation (I/O = 0.76 ± 0.11 and 0.62 ± 0.02), suggesting that lower efficiency filters (< Minimum Efficiency Reporting Value or MERV rating 11) often used in residential and public buildings may not control the infiltration of smaller smoke particles during a wildfire event. Although this study had a small sample size, the limited data collected here indicates that sheltering in a closed, non-ventilated building may be an effective strategy to reduce exposure to particulate matter during wildfires, given that there are no significant indoor source(s) of particulates and that the air leakage is insignificant. Finally, this study also shows that particulate mass concentrations (μg/m3) may not fully describe the relative differences between indoor and outdoor air quality especially during wildfire episodes.

Here we report the ice nucleating temperatures of marine aerosols sampled in the subarctic Atlantic Ocean during a phytoplankton bloom. Ice nucleation measurements were conducted on primary aerosol samples and phytoplankton isolated from seawater samples. Primary marine aerosol samples produced by a specialized aerosol generator (the Sea Sweep) catalyzed droplet freezing at temperatures between −33.4 °C and − 24.5 °C, with a mean freezing temperature of −28.5 °C, which was significantly warmer than the homogeneous freezing temperature of pure water in the atmosphere (−36 °C). Following a storm‐induced deep mixing event, ice nucleation activity was enhanced by two metrics: (1) the fraction of aerosols acting as ice nucleating particles (INPs) and (2) the nucleating temperatures, which were the warmest observed throughout the project. Seawater samples were collected from the ocean's surface and phytoplankton groups, including Synechococcus, picoeukaryotes, and nanoeukaryotes, were isolated into sodium chloride sheath fluid solution using a cell‐sorting flow cytometer. Marine aerosol containing Synechococcus, picoeukaryotes, and nanoeukaryotes serves as INP at temperatures significantly warmer than the homogeneous freezing temperature of pure water in the atmosphere. Samples containing whole organisms in 30 g L−1 NaCl had freezing temperatures between −33.8 and − 31.1 °C. Dilution of samples to representative atmospheric aerosol salt concentrations (as low as 3.75 g L−1 NaCl) raised freezing temperatures to as high as −22.1 °C. It follows that marine aerosols containing phytoplankton may have widespread influence on marine ice nucleation events by facilitating ice nucleation.

Observations from a wintertime and summertime field campaign are used to assess the relationship between black and brown carbon (BC and BrC, respectively) optical properties and particle composition and coating state. The wintertime campaign, in Fresno, CA, was impacted by primary emissions from residential wood burning, secondary organic and inorganic particle formation, and BC from motor vehicles. Two major types of BrC were observed in wintertime. One occurred primarily at night—the result of primary biomass burning emissions. The second was enhanced in daytime and strongly associated with particulate nitrate and the occurrence of fog. The biomass‐burning‐derived BrC absorbed more strongly than the nitrate‐associated BrC but had a weaker wavelength dependence. The wintertime BC‐specific mass absorption coefficient (MACBC) exhibited limited dependence on the ensemble‐average coating‐to‐BC mass ratio (Rcoat‐rBC) at all wavelengths, even up to Rcoat‐rBC of ~5. For the summertime campaign, in Fontana, CA, BC dominated the light absorption, with negligible BrC contribution even after substantial photochemical processing. The summertime MACBC exhibited limited dependence on Rcoat‐rBC, even up to ratios of >10. Based on the four classes of BC‐containing particles identified by Lee et al. (2017, https://doi.org/10.5194/acp‐17‐15055‐2017) for the summertime measurements, the general lack of an absorption enhancement can be partly—although not entirely—attributed to an unequal distribution of coating materials between the BC‐containing particle types. These observations demonstrate that in relatively near‐source environments, even those impacted by strong secondary aerosol production, the ensemble‐average, mixing‐induced absorption enhancement for BC due to coatings can be quite small.

The mixing state of black carbon (BC) affects its environmental fate and impacts. This work investigates particle diversity and mixing state for refractory BC (rBC) containing particles in an urban environment. The chemical compositions of individual rBC-containing particles were measured, from which a mixing state index and particle diversity were determined. The mixing state index (χ) varied between 26% and 69% with the average of 48% in this study and was slightly enhanced with the photochemical age of air masses, indicating that most of the rBC-containing particles cannot be simply explained by fully externally and internally mixed model. Clustering of single particle measurements was used to investigate the potential effects of different primary emissions and atmospheric processes on rBC-containing particle diversity and mixing state. The average particle species diversity and the bulk population species diversity both increased with primary traffic emissions and elevated nitrate concentrations in the morning but gradually decreased with secondary organic aerosol (SOA) formation in the afternoon. The single particle clustering results illustrate that primary traffic emissions and entrainment of nitrate-containing rBC particles from the residual layer to the surface could lead to more heterogeneous aerosol compositions, whereas substantial fresh SOA formation near vehicular emissions made the rBC-containing particles more homogeneous. This work highlights the importance of considering particle diversity and mixing state for investigating the chemical evolution of rBC-containing particles and the potential effects of coating on BC absorption enhancement.

Biogenic sources contribute to cloud condensation nuclei (CCN) in the clean marine atmosphere, but few measurements exist to constrain climate model simulations of their importance. The chemical composition of individual atmospheric aerosol particles showed two types of sulfate-containing particles in clean marine air masses in addition to mass-based Estimated Salt particles. Both types of sulfate particles lack combustion tracers and correlate, for some conditions, to atmospheric or seawater dimethyl sulfide (DMS) concentrations, which means their source was largely biogenic. The first type is identified as New Sulfate because their large sulfate mass fraction (63% sulfate) and association with entrainment conditions means they could have formed by nucleation in the free troposphere. The second type is Added Sulfate particles (38% sulfate), because they are preexisting particles onto which additional sulfate condensed. New Sulfate particles accounted for 31% (7 cm −3 ) and 33% (36 cm −3 ) CCN at 0.1% supersaturation in late-autumn and late-spring, respectively, whereas sea spray provided 55% (13 cm −3 ) in late-autumn but only 4% (4 cm −3 ) in late-spring. Our results show a clear seasonal difference in the marine CCN budget, which illustrates how important phytoplankton-produced DMS emissions are for CCN in the North Atlantic.

Organic aerosol mass (OM) components were investigated at Fresno in winter and at Fontana in summer by positive matrix factorization of high-resolution time-of-flight aerosol mass spectra and of Fourier Transform infrared spectra, as well as by k-means clustering of light-scattering (LS) aerosol single-particle spectra. The results were comparable for all three methods at both sites, showing different contributions of primary and secondary organic aerosol sources to PM1. At Fresno biomass burning organic aerosol contributed 27% of OM on low-fog days, and nitrate-related oxidized OA (NOOA) accounted for 47% of OM on high-fog days, whereas at Fontana very oxygenated organic aerosol (VOOA) components contributed 58-69% of OM. Amine and organosulfate fragment concentrations were between 2 and 3 times higher on high-fog days than on low-fog days at Fresno, indicating increased formation from fog-related processes. NOOA and biomass burning organic aerosol components were largely on different particles than the VOOA components in Fresno, but in Fontana both NOOA and VOOA components were distributed on most particle types, consistent with a longer time for and a larger contribution from gas-phase photochemical secondary organic aerosol formation in summer Fontana than winter Fresno. Uncommon trace organic fragments, elevated inorganic, and alcohol group submicron mass concentrations persisted at Fontana for more than 5days after 4 July fireworks. These unique aerosol chemical compositions at Fresno and Fontana show substantial and extended air-quality impacts from residential burning and fireworks.

Size-resolved composition of atmospheric aerosol particles during winter (19 December 2014 to 13 January 2015) in the San Joaquin Valley at Fresno and during summer (4 to 28 July 2015) in the Southern California Air Basin at Fontana were measured by aerosol mass spectrometer, Fourier transform infrared spectrometer, single particle soot photometer, and scanning electrical mobility sizer. The Fresno study had low-fog and high-fog winter conditions, and residential burning was a frequent contributor to evening emissions. Fireworks during Fourth of July celebrations characterized the start of the Fontana study; the remaining days were categorized as nonfirework days and were mostly affected by traffic emissions. Fresno had particle distributions with number mode diameters of 70-150 nm, and Fontana had 30-50-nm diameters. The nonrefractory organic mass mode diameters were also larger at Fresno (250-380 nm in dry mobility diameter) than at Fontana (130-150 nm, 280 nm in dry mobility diameter) as were refractory black carbon particles (Fresno: 80-180 nm; Fontana: 80-100 nm in dry volume equivalent diameter). The size dependence of organic contributions to particle mass indicated that condensation or other surface-limited processes contributed oxidized organic fractions to aerosol mass in Fontana but that volume-limited aqueous reactions produced organic mass on both low-fog and high-fog days in Fresno. Linear regression analysis of organic aerosol sources with size-resolved particle volume at different times of day also showed that residential burning-related particles increased from 70-160 nm in the evening (18:00 to 23:59) to 150-260 nm at night (00:00 to 05:59) on low-fog days.