ACS ES&T Air最新文献

We investigated the light-absorption properties of brown carbon (BrC) as part of the Georgia Wildland-Fire Simulation Experiment. We constructed fuel beds representative of three ecoregions in the Southeastern U.S. and varied the fuel-bed moisture content to simulate either prescribed fires or drought-induced wildfires. Based on decreasing fire radiative energy normalized by fuel-bed mass loading (FRE_norm), the combustion conditions were grouped into wildfire (Wild), prescribed fire (Rx), and wildfire involving duff ignition (WildDuff). The emitted BrC ranged from weakly absorbing (WildDuff) to moderately absorbing (Rx and Wild) with the imaginary part of the refractive index (k) values that were well-correlated with FRE_norm. We apportioned the BrC into water-soluble (WSBrC) and water-insoluble (WIBrC). Approximately half of the WSBrC molecules detected using electrospray-ionization mass spectrometry were potential chromophores. Nevertheless, k of WSBrC was an order of magnitude smaller than k of WIBrC. Furthermore, k of WIBrC was well-correlated with FRE_norm while k of WSBrC was not, suggesting different formation pathways between WIBrC and WSBrC. Overall, the results signify the importance of combustion conditions in determining BrC light-absorption properties and indicate that variables in wildland fires, such as moisture content and fuel-bed composition, impact BrC light-absorption properties to the extent that they influence combustion conditions.

This study reports that the difference in intensity between prescribed fires and drought-induced wildfires leads to differences in optical properties of light-absorbing organic aerosol in the emissions.

We aim to understand how changes in ambient fine particulate matter (PM_2.5) over the last two decades have influenced PM_2.5-attributable mortality in a Canadian population experiencing both growth and changing baseline health status. We conducted a health impact analysis using dynamic estimates of population, baseline mortality rates, and satellite-based PM_2.5 concentrations to estimate mortality attributable to long-term PM_2.5 exposure every five years between 2001 and 2021, applying risk estimates from the 2006 Canadian Census Health and Environment Cohort (CanCHEC) to the population aged 25 and older. We conducted a decomposition analysis to examine the influences of population exposure, size, and health status on trends in PM_2.5-attributable mortality. Between 2001 and 2021, population-weighted exposure to PM_2.5 declined by 18% in Canada, with improvements occurring in most urban areas. In recent years, these changes have led to 4,400 (95% CI: 3,700–5,000) to 4,700 (95% CI: 4,100–5,400) fewer PM_2.5-attributable deaths annually based on log–linear and log–log shapes of concentration–response. However, a growing population alongside higher baseline mortality risks in several regions, likely due to aging, has led to a small net increase in total PM_2.5-attributable deaths between 2001 and 2021. These findings suggest that the Canadian population has benefitted broadly from air quality management strategies implemented in North America over recent decades.

Limited research exists on the health benefits of air quality improvements achieved in recent years in Canada. This study finds that improvements in fine particulate matter (PM_2.5) exposure have led to thousands of fewer PM_2.5-attributable deaths annually in recent years.

Air pollution from residential wood heating (RWH) presents challenges at the intersection of climate and public health. With a revised National Ambient Air Quality Standard (NAAQS, at 9 μg/m³) for particulate matter (PM) in the United States (U.S.), the Environmental Protection Agency (EPA) will likely classify new non-attainment areas due primarily to emissions from RWH. Agencies will use emissions factors (EFs) to develop attainment strategies. Many will rely on EPA modeling platforms based on data from the National Emissions Inventory (NEI). The NEI uses RWH EFs based on data from mid-1990's in-situ studies and a speciation profile from a 2001 study of fireplace emissions. The NEI does not include greenhouse gas (GHG) emissions for this sector, which plays a key role when assessing climate reduction strategies for the buildings sector. Here, we tested seven wood stoves to determine EFs, representing various vintages and control technologies, using a novel test method that reflects in-use operational settings called the Integrated Duty Cycle. The study measured multiple pollutants concurrently: criteria pollutants (particulate matter [PM], CO, and NOx), nonmethane total hydrocarbons (NMTHCs), GHGs, black carbon (eBC), brown carbon (BrC), and multiple hazardous air pollutants (HAPs). We found no significant difference in PM EFs between uncertified and non-catalytic stove technologies. RWH EF results from this study exceeded 2020 NEI RWH EFs for NMTHC and multiple HAPs. Applying our study's EFs to the 2020 NEI suggests that RWH, compared to all other sources, ranks as the 2nd largest source category of formaldehyde; the 3rd largest of benzene, 1,3-butadiene, and acrolein; and the 4th largest of Pb emissions. RWH also emits more methane compared to natural gas or oil residential heating, raising questions about substitution of wood as a climate neutral heating fuel. However, compared to uncertified stoves, pellet stove EFs (except toxic metals) were significantly lower (p < 0.01). In summary, RWH appears to be an underestimated source of PM (non-catalytic technology), methane, NMTHC, toxic metals, and other HAPs, which has important implications for climate and public health policy in the U.S. and globally.

Air pollution from residential wood heating (RWH) presents challenges at the intersection of climate and public health. With a revised National Ambient Air Quality Standard (NAAQS, at 9 μg/m³) for particulate matter (PM) in the United States (U.S.), the Environmental Protection Agency (EPA) will likely classify new non-attainment areas due primarily to emissions from RWH. Agencies will use emissions factors (EFs) to develop attainment strategies. Many will rely on EPA modeling platforms based on data from the National Emissions Inventory (NEI). The NEI uses RWH EFs based on data from mid-1990’s in-situ studies and a speciation profile from a 2001 study of fireplace emissions. The NEI does not include greenhouse gas (GHG) emissions for this sector, which plays a key role when assessing climate reduction strategies for the buildings sector. Here, we tested seven wood stoves to determine EFs, representing various vintages and control technologies, using a novel test method that reflects in-use operational settings called the Integrated Duty Cycle. The study measured multiple pollutants concurrently: criteria pollutants (particulate matter [PM], CO, and NOx), nonmethane total hydrocarbons (NMTHCs), GHGs, black carbon (eBC), brown carbon (BrC), and multiple hazardous air pollutants (HAPs). We found no significant difference in PM EFs between uncertified and non-catalytic stove technologies. RWH EF results from this study exceeded 2020 NEI RWH EFs for NMTHC and multiple HAPs. Applying our study’s EFs to the 2020 NEI suggests that RWH, compared to all other sources, ranks as the 2nd largest source category of formaldehyde; the 3rd largest of benzene, 1,3-butadiene, and acrolein; and the 4th largest of Pb emissions. RWH also emits more methane compared to natural gas or oil residential heating, raising questions about substitution of wood as a climate neutral heating fuel. However, compared to uncertified stoves, pellet stove EFs (except toxic metals) were significantly lower (p < 0.01). In summary, RWH appears to be an underestimated source of PM (non-catalytic technology), methane, NMTHC, toxic metals, and other HAPs, which has important implications for climate and public health policy in the U.S. and globally.

This research utilized a novel stove operation and fueling test method to update decades-old pollutant emissions factors with new data from U.S. EPA-certified woodstoves. Compared to other categories of home heating, RWH is a substantial source of particulate matter, methane, lead, and multiple hazardous air pollutants, with implications for public health and climate in the U.S. and globally.

We report measurements of the absorption Ångström exponent (AAE) and single scattering albedo (SSA) of biomass burning aerosol from the combustion of fuel beds representing three eco-regions of the Southeast U.S. (Piedmont, Coastal Plain, and Blue Ridge Mountains) with moisture content representative of wildfires and prescribed fires. We find a strong correlation between the AAE and SSA for both simulated wildfires (low fuel moisture) and prescribed fires (higher fuel moisture). For wildfires, the AAE and SSA are strongly dependent on the eco-region of the fuel bed and span a much wider range (AAE = 1.3–4.2, SSA = 0.75–0.97) than they do for prescribed fires (AAE = 2.4–3.1, SSA = 0.88–0.96). The AAE and SSA are also found to be correlated with the fraction of total carbon that is elemental carbon (f_EC) for both wildfires and prescribed fires, but the range of f_EC observed (0.02–0.14) from the fuel beds is much smaller than that reported previously from laboratory studies using individual fuels. The observations from the present study suggest that fuel-bed composition and moisture content are significant factors in determining the relative amount of organic material in biomass burning aerosols and, consequentially, their optical properties.

This work investigates how fuel-bed composition and moisture content influence combustion conditions and the corresponding optical properties of the biomass burning aerosols generated.

Multifunctional organic nitrates derived from biogenic volatile organic compounds are important for understanding ozone and secondary organic aerosol production from oxidation reactions in the presence of nitrogen oxides. Their measurement is challenging, in part because the quantification of these compounds is difficult and time consuming due to the techniques required to synthesize and purify authentic standards. We describe a novel online synthesis and separation technique and demonstrate its use for calibration of a chemical ionization mass spectrometer using iodide reagent ions (I^– CIMS) to measure four isomers of isoprene hydroxy nitrate (IHN; C₅H₉NO₄), two isomers of methyl vinyl ketone hydroxy nitrate (MVKHN; C₄H₇NO₅), and four isomers of monoterpene hydroxy nitrate (MTHN; C₁₀H₁₇NO₄). We further apply our separation technique to an isoprene + NO₃ + HO₂ online reactor to calibrate for six isomers of isoprene hydroperoxide nitrate (C₅H₉NO₅). We find a large range of detection sensitivities and ion molecule reactor (IMR) temperature dependencies among the reported analytes measured as iodide (I^–) clusters. We report a wide range of normalized sensitivities (normalized Hz pptv^–1; nHz pptv^–1) normalized by the [I·H₂O]⁻ reagent ion signal for this class of analytes (0.2–82 nHz pptv^–1). The (4,3)-MVKHN isomer is exceptional for its high sensitivity with this ion chemistry (82 ± 5 nHz pptv^–1), which can lead to an inaccurate representation of the organic nitrate budget if a moderate sensitivity is assumed. The I^– CIMS demonstrates a much smaller range of sensitivities to IHNs (10–34 nHz pptv^–1), with the two most abundant isomers having similar sensitivities ((1,2): 24 ± 3 nHz pptv^–1; (4,3): 30 ± 4 nHz pptv^–1). These calibrations reveal a significantly different distribution of organic nitrates than would be determined assuming uniform sensitivity for measurements with an I^– CIMS at a ground site in Pasadena, CA, during the summer of 2021. A comparison with another calibrated CIMS (using CF₃O^– reagent ions) for select compounds showed good agreement for IHN and MVKHN.

The photooxidation of five anthropogenic volatile organic compounds (propane, propene, isopentane, n-hexane, trans-2-hexene) at different levels of nitric oxide (NO) was investigated in the atmospheric simulation chamber SAPHIR, Forschungszentrum Jülich. Measured time series of trace gases and radical concentrations are compared to zero-dimensional box model calculations, based on the Master Chemical Mechanism (agreement within 30%) and complemented by state-of-the-art structure–activity relationships (SAR). Including RO₂ isomerization reactions from SAR, validated with theoretical calculations, improves particularly the model–measurement agreement by ∼20% for n-hexane. The photooxidation of the chosen compounds generates different types of peroxy radicals (RO₂) which produce HO₂ after one or multiple RO₂+NO reaction steps, depending on the formed alkoxy radical (RO). Measurements show that the HO₂/RO₂ ratio is up to ∼40% lower and the number of odd oxygen (O_x = O₃+NO₂) formed per OH+VOC reaction $\left({P\left(O_x\right)}_{VOC}\right)$ is up to ∼30% higher if RO regenerates RO₂ instead of forming HO₂ directly. Though, the formation of organic nitrates nearly completely compensates for the ozone production from the second NO reaction step for nitrate yields higher than 20%. Measured and modelled HO₂/RO₂ ratios agree well as does $P{\left(O_x\right)}_{VOC}$, derived from measured/modelled radical concentrations and calculated from measured O_x.

A large model−measurement discrepancy of ozone production rates was observed, especially in urban environments. This study highlights that VOCs forming HO₂ after several RO₂+NO reaction steps unlikely explain the model−measurement disagreement of the ozone production, observed in field campaigns.

In Houston, Texas, nitrogen dioxide (NO₂) air pollution disproportionately affects Black, Latinx, and Asian communities, and high ozone (O₃) days are frequent. There is limited knowledge of how NO₂ inequalities vary in urban air quality contexts, in part from the lack of time-varying neighborhood-level NO₂ measurements. First, we demonstrate that daily TROPOspheric Monitoring Instrument (TROPOMI) NO₂ tropospheric vertical column densities (TVCDs) resolve a major portion of census tract-scale NO₂ inequalities in Houston, comparing NO₂ inequalities based on TROPOMI TVCDs and spatiotemporally coincident airborne remote sensing (250 m × 560 m) from the NASA TRacking Aerosol Convection ExpeRiment-Air Quality (TRACER-AQ). We further evaluate the application of daily TROPOMI TVCDs to census tract-scale NO₂ inequalities (May 2018-November 2022). This includes explaining differences between mean daily NO₂ inequalities and those based on TVCDs oversampled to 0.01° × 0.01° and showing daily NO₂ column-surface relationships weaken as a function of observation separation distance. Second, census tract-scale NO₂ inequalities, city-wide high O₃, and mesoscale airflows are found to covary using principal component and cluster analysis. A generalized additive model of O₃ mixing ratios versus NO₂ inequalities reproduces established nonlinear relationships between O₃ production and NO₂ concentrations, providing observational evidence that neighborhood-level NO₂ inequalities and O₃ are coupled. Consequently, emissions controls specifically in Black, Latinx, and Asian communities will have co-benefits, reducing both NO₂ disparities and high O₃ days city wide.

In Houston, Texas, nitrogen dioxide (NO₂) air pollution disproportionately affects Black, Latinx, and Asian communities, and high ozone (O₃) days are frequent. There is limited knowledge of how NO₂ inequalities vary in urban air quality contexts, in part from the lack of time-varying neighborhood-level NO₂ measurements. First, we demonstrate that daily TROPOspheric Monitoring Instrument (TROPOMI) NO₂ tropospheric vertical column densities (TVCDs) resolve a major portion of census tract-scale NO₂ inequalities in Houston, comparing NO₂ inequalities based on TROPOMI TVCDs and spatiotemporally coincident airborne remote sensing (250 m × 560 m) from the NASA TRacking Aerosol Convection ExpeRiment–Air Quality (TRACER-AQ). We further evaluate the application of daily TROPOMI TVCDs to census tract-scale NO₂ inequalities (May 2018–November 2022). This includes explaining differences between mean daily NO₂ inequalities and those based on TVCDs oversampled to 0.01° × 0.01° and showing daily NO₂ column-surface relationships weaken as a function of observation separation distance. Second, census tract-scale NO₂ inequalities, city-wide high O₃, and mesoscale airflows are found to covary using principal component and cluster analysis. A generalized additive model of O₃ mixing ratios versus NO₂ inequalities reproduces established nonlinear relationships between O₃ production and NO₂ concentrations, providing observational evidence that neighborhood-level NO₂ inequalities and O₃ are coupled. Consequently, emissions controls specifically in Black, Latinx, and Asian communities will have co-benefits, reducing both NO₂ disparities and high O₃ days city wide.

Most neighborhood-level NO₂ inequalities can be observed with daily TROPOspheric Monitoring Instrument (TROPOMI) observations; the unequal NO₂ distribution affects O₃ chemistry in Houston, Texas.