United States wildfire smoke polution and associated health impacts
Wildfire smoke distribution and health impacts
Smoke from increasingly frequent and intense wildfires has become a leading cause of air quality exceedances and a growing public health concern in the U.S. (Xie et al., Geophysical Research Letters, 2020; Xie et al, Proceedings of the National Academy of Science, 2022). These increasing smoke concentrations have offset decades of progress achieved by the Clean Air Act’s successful control of anthropogenic emissions of air pollutants. Following my invited conversation with Nature Communications on concerns about the role of increasing wildfire smoke on air quality in the U.S. (Mauzerall et al., Nature Communications, 2021), my group has investigated how increasing fire smoke affects our ability to meet air quality standards over the United States. Our results show that wildfire smoke is becoming an important, and in some counties, a dominant source of fine particulate (PM2.5) pollution. However, under the EPA’s Exceptional Events framework, these smoke impacts can be excluded from nonattainment designations in most counties with annual PM2.5 above the standard, leaving millions of residents chronically exposed to PM2.5 pollution that exceeds the federal standard (Xie et al. in revision). We also estimate smoke-related premature mortalities based on fire-specific concentration response functions and account for changing sociodemographic patterns across U.S. counties over the past decades (Xie et al., in revision) and in a warming climate (Xie et al., in prep). These findings are visualized through a web-based interface designed to help decision-makers identify wildfire contributions to total observed PM2.5, support nonattainment designations, and provide county-level assessments of health impacts and their key drivers over the past three decades (https://usfirepollution.mauzerall.scholar.princeton.edu/ ).
Indian air pollution and associated health impacts
PM2.5 Air Pollution Dashboard for India
India’s air pollution is among the worst in the world, with severe consequences for public health and agricultural productivity. In response, the Indian government implemented the National Clean Air Programme (NCAP) to reduce particulate matter (both PM10 and PM2.5 – particulate matter with diameter less than 10 μm and 2.5μm, respectively) pollution and protect public health. We have published some of the first papers that use the expanding surface continuous monitoring network operated by the national government (Sharma and Mauzerall, Aerosol and Air Quality Research, 2022) to evaluate pollution trends, how meteorological factors influence those trends, and to assess the implications of meteorology on evaluating the effectiveness of the NCAP and seasonal predictability of pollution (Xie et al., Nature Sustainability, 2024, Xie et al., Science Advances, accepted). We also examine how climate change and feedback from changing aerosol emissions affect meteorological patterns and future air pollution management (Zhou et al., Nature Communications, 2024). We highlight the importance of integrating short‑term meteorological variability and long‑term climate change into air quality management strategies to enable more targeted and adaptive policy interventions. To support air pollution management, we have also conducted detailed source apportionment studies using the WRF-Chem atmospheric chemistry model (Zhou et al., Atmospheric Chemistry Physics, accepted), and our ongoing work is examining city-level pollution trends, control policies and mitigation strategies across Indian cities (Xie et al., in preparation) as well as identifying key power sector emission controls to minimize health impacts (Zhou et al., in prep). To support outreach to Indian policymakers, we have developed a web‑based interface that allows users to explore air pollution in various cities including the number and location of monitoring stations, pollution trends across annual, seasonal, and daily timescales, pollution sources to which PM2.5 concentrations can be attributed (source apportionment), and associated health impacts. (https://indiaairpollution.mauzerall.scholar.princeton.edu/)
MOZART-2
Animations of MOZART-2 results -- long-range transport
We have helped develop a global three-dimensional chemical transport model called Model of Ozone and Related Chemical racers, version 2 (MOZART-2). Horowitz et al. (2003) includes a description and evaluation of MOZART-2. This model is built on the framework of the National Center for Atmospheric Research (NCAR) Model of Atmospheric Transport and Chemistry (MATCH). The animations of chemical tracer transport shown here use the standard configuration of the model, which is driven by meteorological inputs every 3 hours from the middle atmosphere version of the NCAR Community Climate Model (MACCM3). The simulations use a 20-min time step and a horizontal resolution of 2.8° latitude by 2.8°longitude with 34 vertical levels extending up to approximately 40 km. MOZART-2 includes a detailed chemistry scheme for tropospheric ozone, nitrogen oxides, and hydrocarbon chemistry, with 63 chemical species. Tracer advection is performed using a flux-form semi-Lagrangian scheme with a pressure fixer with the inclusion of subgrid-scale convective and boundary layer parameterizations. Surface emissions include sources from fossil fuel combustion, biofuel and biomass burning, biogenic and soil emissions, and oceanic emissions. Parameterizations of dry and wet deposition are included. Stratospheric concentrations of several long-lived species (including ozone) are constrained by relaxation toward climatological values.
Animations are based on 1990 emissions and projected 2020 emissions. To simulate the concentration of chemical species in 2020 we used the 2001 Intergovernmental Panel on Climate Change (IPCC) B2-Message scenario to scale the spatially and temporally varying 1990 anthropogenic emissions used in MOZART-2. The IPCC developed emission scenarios following story lines. The B2 scenario family is intended to represent one where there is moderate population growth, intermediate levels of economic development, increased concern for environmental and social sustainability. Hence, it is not a “worst-case” scenario.
Both the 1990 and 2020 animations include the global distributions of total O3, CO, PAN, HNO3 and NOx. In addition, for each region (North America, Europe, East Asia, Former Soviet Union, Tropical Asia, Africa, and South America), and emission type (fossil fuel combustion and biomass burning) we have conducted “tagged” simulations. In these tagged simulations, the emissions of CO and NOx (including its oxidation species HNO3 and PAN) from one region of the world are separately identified and tracked through their chemical transformations and global transport. The distribution of tagged tracers are shown in two panels – the top panel shows, at any given location, the percentage of the chemical species that originated from the particular region as a fraction of the global total, and the bottom panel shows the actual concentration of the tracer.