Global Chemical Transport Model Research Articles

Future Projection of Mortality From Exposure to PM2.5 and O3 Under the Carbon Neutral Pathway: Roles of Changing Emissions and Population Aging

AbstractA global chemical transport model GEOS‐Chem was applied to examine the concentrations of PM2.5 and O3 in China, related health burdens and the relative importance of changes in air pollutants and population aging over 2015–2060 under carbon neutral pathway (Shared Socioeconomic Pathway limiting end‐of‐century radiative forcing to 1.9 W m−2, SSP1‐1.9). Results showed synergistic reductions of 100.0%, 72.0%, and 24.4% in net CO2 emission, concentration of annual mean PM2.5, and the 90th maximum daily average 8‐hr (MDA8) O3 over China, respectively, during 2015–2060. Pollutants‐related deaths owing to changes in pollutants and population were simulated to increase by 38.1% over 2015–2060 because of population aging. Over 2015–2060, sensitivity studies showed that the decline in pollutants alone would mitigate deaths by 5,172.7 thousand, while the population aging alone would increase deaths by 2,633.3 thousand. Carbon neutrality will avoid 3,520.0 thousand deaths in 2060 relative to a higher‐carbon pathway (SSP5‐8.5).

Global nitrogen and sulfur deposition mapping using a measurement–model fusion approach

Abstract. Global reactive nitrogen (N) deposition has more than tripled since 1860 and is expected to remain high due to food production and fossil fuel consumption. Global sulfur emissions have been decreasing worldwide over the last 30 years, but many regions are still experiencing unhealthily high levels of deposition. We update the 2010 global deposition budget for reactive nitrogen and sulfur components with new regional wet deposition measurements from Asia, improving the ensemble results of 11 global chemistry transport models from the second phase of the United Nations Economic Commission for Europe's Task Force on Hemispheric Transport of Air Pollution (HTAP II). The observationally adjusted global N deposition budget is 114.5 Tg N, representing a minor increase of 1 % from the model-only derived values, and the adjusted global sulfur deposition budget is 88.9 Tg S, representing a 6.5 % increase from the modeled values, using an interpolation distance of 2.5∘. Regionally, deposition adjustments can be up to ∼ 73 % for nitrogen and 112 % for sulfur. Our study demonstrates that a global measurement–model fusion approach can improve N and S deposition model estimates at a regional scale, with sufficient availability of observations; however, in large parts of the world, alternative approaches need to be explored. The analysis presented here represents a step forward toward the World Meteorological Organization's goal of global fusion products for accurately mapping harmful air pollution deposition.

Direct gas-phase formation of formic acid through reaction of Criegee intermediates with formaldehyde

Ozonolysis of isoprene is considered to be an important source of formic acid (HCOOH), but its underlying reaction mechanisms related to HCOOH formation are poorly understood. Here, we report the kinetic and product studies of the reaction between the simplest Criegee intermediate (CH2OO) and formaldehyde (HCHO), both of which are the primary products formed in ozonolysis of isoprene. By utilizing time-resolved infrared laser spectrometry with the multifunctional dual-comb spectrometers, the rate coefficient kCH2OO+HCHO is determined to be (4.11 ± 0.25) × 10−12 cm3 molecule−1 s−1 at 296 K and a negative temperature dependence of the rate coefficient is observed and described by an Arrhenius expression with an activation energy of (–1.81 ± 0.04) kcal mol−1. Moreover, the branching ratios of the reaction products HCOOH + HCHO and CO + H2O + HCHO are explored. The yield of HCOOH is obtained to be 37–54% over the pressure (15–60 Torr) and temperature (283–313 K) ranges. The atmospheric implications of the reaction CH2OO + HCHO are also evaluated by incorporating these results into a global chemistry-transport model. In the upper troposphere, the percent loss of CH2OO by HCHO is found by up to 6% which can subsequently increase HCOOH mixing ratios by up to 2% during December-January-February months.

Response of Arctic Black Carbon Contamination and Climate Forcing to Global Supply Chain Relocation.

Black carbon (BC) plays a vital role in Arctic warming. Extensive investigations have been conducted to elucidate the source-receptor relationships of BC between the Arctic and mid-/high-latitude sources. However, it is unclear to what extent source relocation under globalization could disturb Arctic BC contamination and climate forcing from anthropogenic BC emissions. Here, we show that the global supply chain (GSC) relocation featured by the southward shift of industries from high-latitude developed countries to low-latitude developing countries markedly reduces the BC burden in the Arctic using a global chemical transport model (GEOS-Chem) and a multiregional input-output analysis (MRIO). We find that Arctic annual mean BC concentration associated with the GSC relocation drops by ∼15% from the case without the GSC relocation. The total net BC level declines 7% over the entire Arctic and 16% in the European Arctic. We also observed markedly declining BC deposition as well as direct and snow albedo radiative forcing in the Arctic. We show that the Arctic BC burden would be further reduced by decreasing BC emissions in China, attributable to its emission reduction and ongoing shift of the GSC from China to southern and southeastern Asia.

Parameterization of size of organic and secondary inorganic aerosol for efficient representation of global aerosol optical properties

Abstract. Accurate representation of aerosol optical properties is essential for the modeling and remote sensing of atmospheric aerosols. Although aerosol optical properties are strongly dependent upon the aerosol size distribution, the use of detailed aerosol microphysics schemes in global atmospheric models is inhibited by associated computational demands. Computationally efficient parameterizations for aerosol size are needed. In this study, airborne measurements over the United States (DISCOVER-AQ) and South Korea (KORUS-AQ) are interpreted with a global chemical transport model (GEOS-Chem) to investigate the variation in aerosol size when organic matter (OM) and sulfate–nitrate–ammonium (SNA) are the dominant aerosol components. The airborne measurements exhibit a strong correlation (r=0.83) between dry aerosol size and the sum of OM and SNA mass concentration (MSNAOM). A global microphysical simulation (GEOS-Chem-TOMAS) indicates that MSNAOM and the ratio between the two components (OM/SNA) are the major indicators for SNA and OM dry aerosol size. A parameterization of the dry effective radius (Reff) for SNA and OM aerosol is designed to represent the airborne measurements (R2=0.74; slope = 1.00) and the GEOS-Chem-TOMAS simulation (R2=0.72; slope = 0.81). When applied in the GEOS-Chem high-performance model, this parameterization improves the agreement between the simulated aerosol optical depth (AOD) and the ground-measured AOD from the Aerosol Robotic Network (AERONET; R2 from 0.68 to 0.73 and slope from 0.75 to 0.96). Thus, this parameterization offers a computationally efficient method to represent aerosol size dynamically.

Contamination of tea leaves by anthraquinone: The atmosphere as a possible source

The detection of anthraquinone in tea leaves has raised concerns due to a potential health risk associated with this species. This led the European Union to impose a maximum residue limit (MRL) of 0.02 mg/kg for anthraquinone in dried tea leaves. As atmospheric contamination has been identified as one of the possible sources of anthraquinone residue, this study investigates the contamination resulting from the deposition of atmospheric anthraquinone using a global chemical transport model that accounts for the emission, atmospheric transport, chemical transformation, and deposition of anthraquinone on the surface. The largest contribution to the global atmospheric budget of anthraquinone is from residential combustion followed by the secondary formation from oxidation of anthracene. Simulations suggest that atmospheric anthraquinone deposition could be a substantial source of the anthraquinone found on tea leaves in several tea-producing regions, especially near highly industrialized and populated areas of southern and eastern Asia. The high level of anthraquinone deposition in these areas may result in residues in tea products exceeding the EU MRL. Additional contamination could also result from local tea production operations.

Off‐setting climate change through formation flying of aircraft, a feasibility study reliant on high fidelity gas‐phase chemical kinetic data

AbstractApplication of formation flights to civil aviation is gaining interest, primarily due to the fuel burn reduction achieved by flying through another aircraft's wake. However, it is emerging that there are additional, less‐recognized climate benefits via reduction in ozone and contrail warming through this concept. The NOx threshold level is defined as when the loss rate for OH by reaction with NO2 is equal to the loss rates for OH with CO and CH4, beyond which level, ozone formation will decrease. In this study, The NOx threshold level was calculated at different altitudes and found that at cruise altitude (∼10 km), the amount of NO2 required for parity in OH loss with loss due to reaction with CO and CH4 is around 2 ppb. The spatial and temporal NOx threshold levels were estimated by STOCHEM‐Common Representative Intermediate (CRI) global chemical transport model and In‐service Aircraft for Global Observing System (IAGOS) measurement data and found that northern midlatitudes of the atmosphere are the most favorable region existing with the smallest NOx thresholds (0.5 ppb) needed before reduction in ozone formation is likely to occur at cruise altitude of aircraft. Incorporating the major air traffic corridors into the coarse spatial resolution of the chemical transport model overestimated the NOx compensation point, that is, increased photochemical ozone production. Thus, a simple one‐dimensional (1D) aircraft plume dispersion model was developed with higher spatial and temporal resolution for considering aircraft plumes and its chemistry more accurately. The model run shows that the impact of formation flying aircraft emissions on spatially averaged ozone could be halved if the aircraft could maintain separations inside 4 km relative to well separated flights of 10 km or more.

Analysis of new particle formation events and comparisons to simulations of particle number concentrations based on GEOS-Chem–advanced particle microphysics in Beijing, China

Abstract. Aerosol particles play important roles in air quality and global climate change. In this study, we analyze the measurements of particle size distribution from 12 March to 6 April 2016 in Beijing to characterize new particle formation (NPF) using the observational data of sulfuric acid, meteorological parameters, solar radiation, and the mass concentration of fine particles (PM2.5, particulate matter with diameters less than 2.5 µm). During this 26 d campaign, 11 new particle formation events are identified with obvious bursts of sub-3 nm particle number concentrations and subsequent growth of these nucleated particles. It is found that sulfuric acid concentration in Beijing does not have a significant difference between NPF event and non-event days. Low relative humidity (RH) and high daily total solar radiation appear to be favorable for the occurrence of NPF events, which is quite obvious in this campaign. The simulations using four nucleation schemes, i.e., H2SO4–H2O binary homogeneous nucleation (BHN), H2SO4–H2O–NH3 ternary homogeneous nucleation (THN), H2SO4–H2O–ion binary ion-mediated nucleation (BIMN), and H2SO4–H2O–NH3–ion ternary ion-mediated nucleation (TIMN), based on a global chemistry transport model (GEOS-Chem) coupled with an advanced particle microphysics (APM) model, are conducted to study the particle number concentrations and new particle formation process. Our comparisons between measurements and simulations indicate that the BHN scheme and BIMN scheme significantly underestimate the observed particle number concentrations, and the THN scheme captures the total particle number concentration on most NPF event days well but fails to capture the noticeable increase in particle number concentrations on 18 March and 1 April. The TIMN scheme has obvious improvement in terms of total and sub-3 nm particle number concentrations and nucleation rates. This study provides a basis for further understanding of the nucleation mechanism in Beijing.

Impacts of different biomass burning emission inventories: Simulations of atmospheric CO2 concentrations based on GEOS-Chem

Biomass burning has substantial spatiotemporal variabilities. It contributes significantly to the dynamics of global CO2 distributions and variances. Quantifying the impacts of biomass burning emissions on atmospheric CO2 concentrations is essential for global and regional carbon cycles and budgets. In this study, we performed several numerical experiments by switching and replacing inventories to estimate the impacts of four biomass burning emission inventories on atmospheric CO2 concentration simulations in 2006–2010 based on the global chemical transport model, GEOS-Chem. The results highlighted similarities and differences in the annual and seasonal variability of biomass burning emissions and simulated CO2 concentrations at global and regional scales. Based on four different biomass burning emission inventories, we found that biomass burning emissions could lead to a global CO2 concentration increase of 2.4 ppm annually. Africa contributed the largest global CO2 emissions among all continental regions, where the maximum CO2 concentration increase could reach 7.9–13.0 ppm in summer. Model evaluation results showed that simulation using the Quick Fire Emissions Database (QFED) as the model priori biomass burning emission inventory had the best performance compared with the satellite and surface observations. The sensitivity of simulated CO2 concentrations to the uncertainties in different biomass burning emission inventories was high in southern South America and most areas of the Eurasian continent, and low in central Africa and Southeast Asia. This study furthers our understanding of the critical role of biomass burning in atmospheric CO2 and indicates an urgent need to improve the accuracy of biomass burning emission estimates in CO2 simulations.

Global agricultural ammonia emissions simulated with the ORCHIDEE land surface model

Abstract. Ammonia (NH3) is an important atmospheric constituent. It plays a role in air quality and climate through the formation of ammonium sulfate and ammonium nitrate particles. It has also an impact on ecosystems through deposition processes. About 85 % of NH3 global anthropogenic emissions are related to food and feed production and, in particular, to the use of mineral fertilizers and manure management. Most global chemistry transport models (CTMs) rely on bottom-up emission inventories, which are subject to significant uncertainties. In this study, we estimate emissions from livestock by developing a new module to calculate ammonia emissions from the whole agricultural sector (from housing and storage to grazing and fertilizer application) within the ORCHIDEE (Organising Carbon and Hydrology In Dynamic Ecosystems) global land surface model. We detail the approach used for quantifying livestock feed management, manure application, and indoor and soil emissions and subsequently evaluate the model performance. Our results reflect China, India, Africa, Latin America, the USA, and Europe as the main contributors to global NH3 emissions, accounting for 80 % of the total budget. The global calculated emissions reach 44 Tg N yr−1 over the 2005–2015 period, which is within the range estimated by previous work. Key parameters (e.g., the pH of the manure, timing of N application, and atmospheric NH3 surface concentration) that drive the soil emissions have also been tested in order to assess the sensitivity of our model. Manure pH is the parameter to which modeled emissions are the most sensitive, with a 10 % change in emissions per percent change in pH. Even though we found an underestimation in our emissions over Europe (−26 %) and an overestimation in the USA (+56 %) compared with previous work, other hot spot regions are consistent. The calculated emission seasonality is in very good agreement with satellite-based emissions. These encouraging results prove the potential of coupling ORCHIDEE land-based emissions to CTMs, which are currently forced by bottom-up anthropogenic-centered inventories such as the CEDS (Community Emissions Data System).

Isoprene and monoterpene simulations using the chemistry–climate model EMAC (v2.55) with interactive vegetation from LPJ-GUESS (v4.0)

Abstract. Earth system models (ESMs) integrate previously separate models of the ocean, atmosphere and vegetation into one comprehensive modelling system enabling the investigation of interactions between different components of the Earth system. Global isoprene and monoterpene emissions from terrestrial vegetation, which represent the most important source of volatile organic compounds (VOCs) in the Earth system, need to be included in global and regional chemical transport models given their major chemical impacts on the atmosphere. Due to the feedback of vegetation activity involving interactions with weather and climate, a coupled modelling system between vegetation and atmospheric chemistry is recommended to address the fate of biogenic volatile organic compounds (BVOCs). In this work, further development in linking LPJ-GUESS, a global dynamic vegetation model, to the atmospheric-chemistry-enabled atmosphere–ocean general circulation model EMAC is presented. New parameterisations are included to calculate the foliar density and leaf area density (LAD) distribution from LPJ-GUESS information. The new vegetation parameters are combined with existing LPJ-GUESS output (i.e. leaf area index and cover fractions) and used in empirically based BVOC modules in EMAC. Estimates of terrestrial BVOC emissions from EMAC's submodels ONEMIS and MEGAN are evaluated using (1) prescribed climatological vegetation boundary conditions at the land–atmosphere interface and (2) dynamic vegetation states calculated in LPJ-GUESS (replacing the “offline” vegetation inputs). LPJ-GUESS-driven global emission estimates for isoprene and monoterpenes from the submodel ONEMIS were 546 and 102 Tg yr−1, respectively. MEGAN determines 657 and 55 Tg of isoprene and monoterpene emissions annually. The new vegetation-sensitive BVOC fluxes in EMAC are in good agreement with emissions from the semi-process-based module in LPJ-GUESS. The new coupled system is used to evaluate the temperature and vegetation sensitivity of BVOC fluxes in doubling CO2 scenarios. This work provides evidence that the new coupled model yields suitable estimates for global BVOC emissions that are responsive to vegetation dynamics. It is concluded that the proposed model set-up is useful for studying land–biosphere–atmosphere interactions in the Earth system.

Air pollution mitigation in North China through flexible heating policies

Central heating in North China produces severe air pollution, although the need for heating may be reduced by rising temperatures associated with climate change. The regional trend of mean heating length (HL) for North China was −0.32 d per year during 1961–2019. Compared with the 2010–2015 mean values, the start and end dates for central heating in the North China Plain (NCP) during 2050–2055 will delayed by 9 d and advanced by 12 d, respectively, under the Shared Socioeconomic Pathway 5–8.5 (SSP5-85), and by 5 and 8 d under the carbon-neutral (CN) scenario, based on Coupled Model Intercomparison Project phase 6 model simulations. Here we propose a flexible heating policy (FHP), such that HL is determined strictly by temperature, and the associated air pollution benefit of shortening HL are examined by a global 3D chemical transport model GEOS-Chem. The study focused on the year 2019 with the current goal of elimination of severe PM2.5 pollution, and with the minimum HL estimated to provide up to a 24% reduction in severe PM2.5 pollution (daily mean PM2.5 > 150 μg m−3) over the NCP during periods of FHP implementation. For future CN policies, the NCP can achieve great air quality improvements by 2050, with more than 60% of days throughout the heating season with daily PM2.5 concentrations of <10 μg m−3, and 95% with <35 μg m−3. Although the SSP5-85 scenario may lead to reduced HLs, pollutant emissions are likely much higher than under CN scenarios, with pollution days of PM2.5> 100 μg m−3 still occurring frequently by 2050. Our results highlight that FHPs may effectively reduce severe PM2.5 pollution, and China’s carbon neutrality goals will play critical roles in mitigating air pollution and prolonged heating welfare during future heating season.

Composited analyses of the chemical and physical characteristics of co-polluted days by ozone and PM2.5 over 2013–2020 in the Beijing–Tianjin–Hebei region

Abstract. The co-polluted days by ozone (O3) and PM2.5 (particulate matter with an aerodynamic equivalent diameter of 2.5 µm or less) (O3–PM2.5PDs) were frequently observed in the Beijing–Tianjin–Hebei (BTH) region in warm seasons (April–October) of 2013–2020. We applied the 3-D global chemical transport model (GEOS-Chem) to investigate the chemical and physical characteristics of O3–PM2.5PDs by composited analyses of such days that were captured by both the observations and the model. Model results showed that, when O3–PM2.5PDs occurred, the concentrations of hydroxyl radical and total oxidant, sulfur oxidation ratio, and nitrogen oxidation ratio were all high, and the concentrations of sulfate at the surface were the highest among all pollution types. We also found unique features in vertical distributions of aerosols during O3–PM2.5PDs; concentrations of PM2.5 decreased with altitude near the surface but remained stable at 975–819 hPa. Process analyses showed that secondary aerosols (nitrate, ammonium, and sulfate) had strong chemical productions at 913–819 hPa, which were then transported downward, resulting in the quite uniform vertical profiles at 975–819 hPa on O3–PM2.5PDs. The weather patterns for O3–PM2.5PDs were characterized by anomalous high-pressure system at 500 hPa as well as strong southerlies and high RH at 850 hPa. The latter resulted in the strong chemical productions around 850 hPa on O3–PM2.5PDs. The physical and chemical characteristics of O3–PM2.5PDs are quite different from those of polluted days by either O3 alone or PM2.5 alone and have important implications for air quality management.

Impact of lowering fine particulate matter from major emission sources on mortality in Canada: A nationwide causal analysis

Emissions of fine particulate matter (PM2.5) from human activities have been linked to substantial disease burdens, but evidence regarding how reducing PM2.5 at its sources would improve public health is sparse. We followed a population-based cohort of 2.7 million adults across Canada from 2007 through 2016. For each participant, we estimated annual mean concentrations of PM2.5 and the fractional contributions to PM2.5 from the five leading anthropogenic sources at their residential address using satellite observations in combination with a global atmospheric chemistry transport model. For each source, we estimated the causal effects of six hypothetical interventions on 10-y nonaccidental mortality risk using the parametric g-formula, a structural causal model. We conducted stratified analyses by age, sex, and income. This cohort would have experienced tangible health gains had contributions to PM2.5 from any of the five sources been reduced. Compared with no intervention, a 10% annual reduction in PM2.5 contributions from transportation and power generation, Canada's largest and fifth-largest anthropogenic sources, would have prevented approximately 175 (95%CI: 123-226) and 90 (95%CI: 63-117) deaths per million by 2016, respectively. A more intensive 50% reduction per year in PM2.5 contributions from the two sources would have averted 360 and 185 deaths per million, respectively, by 2016. The potential health benefits were greater among men, older adults, and low-income earners. In Canada, where PM2.5 levels are among the lowest worldwide, reducing PM2.5 contributions from anthropogenic sources by as little as 10% annually would yield meaningful health gains.

Remote Aerosol Simulated During the Atmospheric Tomography (ATom) Campaign and Implications for Aerosol Lifetime.

We investigate and assess how well a global chemical transport model (GEOS-Chem) simulates submicron aerosol mass concentrations in the remote troposphere. The simulated speciated aerosol (organic aerosol (OA), black carbon, sulfate, nitrate, and ammonium) mass concentrations are evaluated against airborne observations made during all four seasons of the NASA Atmospheric Tomography Mission (ATom) deployments over the remote Pacific and Atlantic Oceans. Such measurements over pristine environments offer fresh insights into the spatial (Northern [NH] and Southern Hemispheres [SH], Atlantic, and Pacific Oceans) and temporal (all seasons) variability in aerosol composition and lifetime, away from continental sources. The model captures the dominance of fine OA and sulfate aerosol mass concentrations in all seasons. There is a high bias across all species in the ATom-2 (NH winter) simulations; implementing recent updates to the wet scavenging parameterization improves our simulations, eliminating the large ATom-2 (NH winter) bias, improving the ATom-1 (NH summer) and ATom-3 (NH fall) simulations, but producing a model underestimate in aerosol mass concentrations for the ATom-4 (NH spring) simulations. Following the wet scavenging updates, simulated global annual mean aerosol lifetimes vary from 1.9 to 4.0days, depending on species. Aerosol lifetimes in each hemisphere vary by season, and are longest for carbonaceous aerosol during the southern hemispheric fire season. The updated wet scavenging parameterization brings simulated concentrations closer to observations and reduces global aerosol lifetime for all species, indicating the sensitivity of global aerosol lifetime and burden to wet removal processes.

Satellite-derived constraints on the effect of drought stress on biogenic isoprene emissions in the southeastern US

Abstract. While substantial progress has been made to improve our understanding of biogenic isoprene emissions under unstressed conditions, large uncertainties remain with respect to isoprene emissions under stressed conditions. Here, we use the US Drought Monitor (USDM) as a weekly drought severity index and tropospheric columns of formaldehyde (HCHO), the key product of isoprene oxidation, retrieved from the Ozone Monitoring Instrument (OMI) to derive top-down constraints on the response of summertime isoprene emissions to drought stress in the southeastern United States (SE US), a region of high isoprene emissions that is also prone to drought. OMI HCHO column density is found to be 6.7 % (mild drought) to 23.3 % (severe drought) higher than that under non-drought conditions. A global chemical transport model, GEOS-Chem, with version 2.1 of the Model of Emissions of Gases and Aerosols from Nature (MEGAN2.1) emission algorithm can simulate this direction of change, but the simulated increases at the corresponding drought levels are 1.1–1.5 times that of OMI HCHO, suggesting the need for a drought-stress algorithm in the model. By minimizing the model–OMI differences in HCHO to temperature sensitivity under different drought levels, we derived a top-down drought stress factor (γd_OMI) in GEOS-Chem that parameterizes using water stress and temperature. The algorithm led to an 8.6 % (mild drought) to 20.7 % (severe drought) reduction in isoprene emissions in the SE US relative to the simulation without it. With γd_OMI the model predicts a nonlinear increasing trend in isoprene emissions with drought severity that is consistent with OMI HCHO and a single site's isoprene flux measurements. Compared with a previous drought stress algorithm derived from the latter, the satellite-based drought stress factor performs better with respect to capturing the regional-scale drought–isoprene responses, as indicated by the near-zero mean bias between OMI and simulated HCHO columns under different drought conditions. The drought stress algorithm also reduces the model's high bias in organic aerosol (OA) simulations by 6.60 % (mild drought) to 11.71 % (severe drought) over the SE US compared to the no-stress simulation. The simulated ozone response to the drought stress factor displays a spatial disparity due to the isoprene-suppressing effect on oxidants, with an &lt;1 ppb increase in O3 in high-isoprene regions and a 1–3 ppbv decrease in O3 in low-isoprene regions. This study demonstrates the unique value of exploiting long-term satellite observations to develop empirical stress algorithms on biogenic emissions where in situ flux measurements are limited.

A tool for air pollution scenarios (TAPS v1.0) to enable global, long-term, and flexible study of climate and air quality policies

Abstract. Air pollution is a major sustainability challenge – and future anthropogenic precursor and greenhouse gas (GHG) emissions will greatly affect human well-being. While mitigating climate change can reduce air pollution both directly and indirectly, distinct policy levers can affect these two interconnected sustainability issues across a wide range of scenarios. We help to assess such issues by presenting a public Tool for Air Pollution Scenarios (TAPS) that can flexibly assess pollutant emissions from a variety of climate and air quality actions, through the tool's coupling with socioeconomic modeling of climate change mitigation. In this study, we develop and implement TAPS with three components: recent global and fuel-specific anthropogenic emissions inventories, scenarios of emitting activities to 2100 from the MIT Economic Projection and Policy Analysis (EPPA) model, and emissions intensity trends based on recent scenario data from the Greenhouse Gas–Air Pollution Interactions and Synergies (GAINS) model. An initial application shows that in scenarios with less climate and pollution policy ambition, near-term air quality improvements from existing policies are eclipsed by long-term emissions increases – particularly from industrial processes that combine sharp production growth with less stringent pollution controls in developing regions. Additional climate actions would substantially reduce air pollutant emissions related to fossil fuel (such as sulfur and nitrogen oxides), while further pollution controls would lead to larger reductions for ammonia and organic carbon (OC). Future applications of TAPS could explore diverse regional and global policies that affect these emissions, using pollutant emissions results to drive global atmospheric chemical transport models to study the scenarios' health impacts.

Multi-axis differential optical absorption spectroscopy (MAX-DOAS) observations of formaldehyde and nitrogen dioxide at three sites in Asia and comparison with the global chemistry transport model CHASER

Abstract. Formaldehyde (HCHO) and nitrogen dioxide (NO2) concentrations and profiles were retrieved from ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) observations during January 2017–December 2018 at three sites in Asia: (1) Phimai (15.18∘ N, 102.5∘ E), Thailand; (2) Pantnagar (29∘ N, 78.90∘ E) in the Indo-Gangetic Plain (IGP), India; and (3) Chiba (35.62∘ N, 140.10∘ E), Japan. Retrievals were performed using the Japanese MAX-DOAS profile retrieval algorithm ver. 2 (JM2). The observations were used to evaluate the NO2 and HCHO partial columns and profiles (0–4 km) simulated using the global chemistry transport model (CTM) CHASER (Chemical Atmospheric General Circulation Model for Study of Atmospheric Environment and Radiative Forcing). The NO2 and HCHO concentrations at all three sites showed consistent seasonal variation throughout the investigated period. Biomass burning affected the HCHO and NO2 variations at Phimai during the dry season and at Pantnagar during spring (March–May) and post-monsoon (September–November). Results found for the HCHO-to-NO2 ratio (RFN), an indicator of high ozone sensitivity, indicate that the transition region (i.e., 1 &lt; RFN &lt; 2) changes regionally, echoing the recent finding for RFN effectiveness. Moreover, reasonable estimates of transition regions can be derived, accounting for the NO2–HCHO chemical feedback. The model was evaluated against global NO2 and HCHO columns data retrieved from Ozone Monitoring Instrument (OMI) observations before comparison with ground-based datasets. Despite underestimation, the model well simulated the satellite-observed global spatial distribution of NO2 and HCHO, with respective spatial correlations (r) of 0.73 and 0.74. CHASER demonstrated good performance, reproducing the MAX-DOAS-retrieved HCHO and NO2 abundances at Phimai, mainly above 500 m from the surface. Model results agree with the measured variations within the 1-sigma (1σ) standard deviation of the observations. Simulations at higher resolution improved the modeled NO2 estimates for Chiba, reducing the mean bias error (MBE) for the 0–2 km height by 35 %, but resolution-based improvements were limited to surface layers. Sensitivity studies show that at Phimai, pyrogenic emissions contribute up to 50 % and 35 % to HCHO and NO2 concentrations, respectively.

An improved representation of fire non-methane organic gases (NMOGs) in models: emissions to reactivity

Abstract. Fires emit a substantial amount of non-methane organic gases (NMOGs), the atmospheric oxidation of which can contribute to ozone and secondary particulate matter formation. However, the abundance and reactivity of these fire NMOGs are uncertain and historically not well constrained. In this work, we expand the representation of fire NMOGs in a global chemical transport model, GEOS-Chem. We update emission factors to Andreae (2019) and the chemical mechanism to include recent aromatic and ethene and ethyne model improvements (Bates et al., 2021; Kwon et al., 2021). We expand the representation of NMOGs by adding lumped furans to the model (including their fire emission and oxidation chemistry) and by adding fire emissions of nine species already included in the model, prioritized for their reactivity using data from the Fire Influence on Regional to Global Environments (FIREX) laboratory studies. Based on quantified emissions factors, we estimate that our improved representation captures 72 % of emitted, identified NMOG carbon mass and 49 % of OH reactivity from savanna and temperate forest fires, a substantial increase from the standard model (49 % of mass, 28 % of OH reactivity). We evaluate fire NMOGs in our model with observations from the Amazon Tall Tower Observatory (ATTO) in Brazil, Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) and DC3 in the US, and Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) in boreal Canada. We show that NMOGs, including furan, are well simulated in the eastern US with some underestimates in the western US and that adding fire emissions improves our ability to simulate ethene in boreal Canada. We estimate that fires provide 15 % of annual mean simulated surface OH reactivity globally, as well as more than 75 % over fire source regions. Over continental regions about half of this simulated fire reactivity comes from NMOG species. We find that furans and ethene are important globally for reactivity, while phenol is more important at a local level in the boreal regions. This is the first global estimate of the impact of fire on atmospheric reactivity.

Socioeconomic disparities in aerosol pollutant exposure may be amplified by ultrafine particles despite declining PM2.5

BACKGROUND AND AIM: No study has investigated the spatiotemporal race-ethnicity and income disparities in ultrafine particles (UFP; &amp;#x2264;0.1µm) exposure, which is increasingly identified as a key subcomponent of PM₂.₅-related health effects. This study aims to establish the importance of distinguishing UFP from PM₂.₅ and quantify their race-ethnicity and income disparities in New York State (NYS). METHODS: Exposure disparities among seven race-ethnicity groups (Hispanics of any race, non-Hispanic Asian, Black, Native, Pacific&amp;#x26; White alone, and Other/Mixed) and by household income across spatial scales (state, county, county subdivision, NCHS urban levels) during the period 2013–2020 for UFP and PM₂.₅, were quantified using Census data. A global three-dimensional chemical transport model with state-of-the-science aerosol microphysical processes were used to estimate UFP/PM₂.₅ that have been validated extensively with observations. RESULTS: The average New Yorker was exposed to 5171#·cm⁻³ UFP and 8.2µg·m⁻³ PM₂.₅ in 2013–2020. Minority race-ethnicity groups were invariably exposed to greater daily aerosol pollution in NYS (+51–104% UFP &amp;#x26; +1.9–32% PM₂.₅). Race-ethnicity exposure disparities for PM₂.₅ exposure have declined over time; by −6% from 2013–2017 and plateauing thereafter despite increasing PM₂.₅. Crucially and in contrast, these disparities have persisted (+10%) for UFP exposure and even widened in periods of declining UFP. Economic status (median household income) by itself does not reveal significant exposure disparities. However, in tandem with race-ethnicity it uncovers these disparities as disproportionately magnified for socioeconomically disadvantaged subgroups. CONCLUSIONS: PM₂.₅ decline was associated with decline in race-ethnicity exposure disparities. which continued despite a post-2018 reversal in PM₂.₅ trends. However, race-ethnicity UFP exposure disparities were much larger, more disproportionate, and increased or remained constant across various income strata and levels of urbanicity. The need to distinguish ultrafine (UFP) from fine (PM₂.₅) aerosols is established through microphysical, geostatistical, and exposure assessment perspectives. KEYWORDS: air pollution, ultrafine particles, particulate matter, environmental justice, socioeconomic status