No abstract

The unequal spatial distribution of ambient nitrogen dioxide (NO2), an air pollutant related to traffic, leads to higher exposure for minority and low socioeconomic status communities. We exploit the unprecedented drop in urban activity during the COVID-19 pandemic and use high-resolution, remotely sensed NO2 observations to investigate disparities in NO2 levels across different demographic subgroups in the United States. We show that, prior to the pandemic, satellite-observed NO2 levels in the least White census tracts of the United States were nearly triple the NO2 levels in the most White tracts. During the pandemic, the largest lockdown-related NO2 reductions occurred in urban neighborhoods that have 2.0 times more non-White residents and 2.1 times more Hispanic residents than neighborhoods with the smallest reductions. NO2 reductions were likely driven by the greater density of highways and interstates in these racially and ethnically diverse areas. Although the largest reductions occurred in marginalized areas, the effect of lockdowns on racial, ethnic, and socioeconomic NO2 disparities was mixed and, for many cities, nonsignificant. For example, the least White tracts still experienced ∼1.5 times higher NO2 levels during the lockdowns than the most White tracts experienced prior to the pandemic. Future policies aimed at eliminating pollution disparities will need to look beyond reducing emissions from only passenger traffic and also consider other collocated sources of emissions such as heavy-duty vehicles.

Meteorological variables, such as the ambient temperature and humidity, play a well-established role in the seasonal transmission of respiratory viruses and influenza in temperate climates. Since the onset of the novel coronavirus disease 2019 (COVID-19) pandemic, a growing body of literature has attempted to characterize the sensitivity of COVID-19 to meteorological factors and thus understand how changes in the weather and seasonality may impede COVID-19 transmission. Here we select a subset of this literature, summarize the diversity in these studies' scopes and methodologies, and show the lack of consensus in their conclusions on the roles of temperature, humidity, and other meteorological factors on COVID-19 transmission dynamics. We discuss how several aspects of studies' methodologies may challenge direct comparisons across studies and inflate the importance of meteorological factors on COVID-19 transmission. We further comment on outstanding challenges for this area of research and how future studies might overcome them by carefully considering robust modeling approaches, adjusting for mediating and covariate effects, and choosing appropriate scales of analysis.

Observing the spatial heterogeneities of NO 2 air pollution is an important first step in quantifying NO X emissions and exposures. This study investigates the capabilities of the Tropospheric Monitoring Instrument (TROPOMI) in observing the spatial and temporal patterns of NO 2 pollution in the continental United States. The unprecedented sensitivity of the sensor can differentiate the fine‐scale spatial heterogeneities in urban areas, such as emissions related to airport/shipping operations and high traffic, and the relatively small emission sources in rural areas, such as power plants and mining operations. We then examine NO 2 columns by day‐of‐the‐week and find that Saturday and Sunday concentrations are 16% and 24% lower respectively, than during weekdays. We also analyze the correlation of daily maximum 2‐m temperatures and NO 2 column amounts and find that NO 2 is larger on the hottest days (>32°C) as compared to warm days (26°C–32°C), which is in contrast to a general decrease in NO 2 with increasing temperature at moderate temperatures. Finally, we demonstrate that a linear regression fit of 2019 annual TROPOMI NO 2 data to annual surface‐level concentrations yields relatively strong correlation ( R 2 = 0.66). These new developments make TROPOMI NO 2 satellite data advantageous for policymakers and public health officials, who request information at high spatial resolution and short timescales, in order to assess, devise, and evaluate regulations.

Summertime surface‐level ozone (O3) is known to vary with temperature, but the relative roles of different processes responsible for causing the O3‐temperature relationship are not well quantified. In this study we use simulations of NASA's Global Modeling Initiative chemical transport model to isolate and assess the relative impact of atmospheric transport, chemistry, and emissions on large‐scale O3 variability, events, and and the covariance of O3 with temperature. Using observations from the Clean Air Status and Trends Network in the contiguous United States, we show that the Global Modeling Initiative chemical transport model reproduces the spatiotemporal variability of O3 and its relationship with temperature during the summer. We use the change in O3 given a change in temperature (dO3/dT) along with other metrics to understand differences between our simulations. In regions with moderate to strong positive correlations between temperature and O3 such as the northeast, Great Lakes, and Great Plains, temperature's association with transport yields a majority of the total O3‐temperature relationship (∼60%), while temperature‐dependent chemistry and anthropogenic NO emissions play smaller roles (∼30% and ∼10%, respectively). There are regions, however, with insignificant correlations between temperature and O3, and our findings suggest that transport is still an important driver of O3 variability in these regions, albeit not correlated with temperature. Transport is not directly dependent on temperature but rather is linked through an indirect association, and it is therefore important to understand the exact mechanisms that link transport to O3 and how these mechanisms will change in a warming world.

The body of literature on ambient air pollution suggests that atmospheric stagnation events trigger high levels of air pollution. In this paper we use fifteen years (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014) of summertime in situ air quality measurements together with meteorological reanalysis data to examine the temporal correlation of pollutants with the Air Stagnation Index (ASI) on daily timescales. We find that while the direction of the relationship between the ASI and summertime PM 2.5 and O 3 ranges from near-zero to positive throughout regions comprising the contiguous United States (US), the strength of the relationship is very weak (e.g. in the Northeast the correlation coefficient between the ASI and PM 2.5 is 0.09). Moreover, similar to our analysis of the correlation of day-to-day variations of the ASI and pollutants, the percentage of co-occurring extreme pollution and stagnation events is small (e.g. days with a high coverage of stagnation only co-occur with extreme pollution events about one-third of the time in the Northeast). The southern US is an exception to our overall findings as the strength of the relationship between the ASI and pollution is stronger and the percentage of co-occurring events is higher compared with other regions. The results of this study suggest a reevaluation of the ASI as an index to assess meteorological and climatic impacts to air quality.

Ambient nitrogen dioxide (NO2) and fine particulate matter (PM2.5) pollution threaten public health in the United States (U.S.), and systemic racism has led to modern-day disparities in the distribution and associated health impacts of these pollutants. Many studies on environmental injustices related to ambient air pollution focus only on disparities in pollutant concentrations or provide only an assessment of pollution or health disparities at a snapshot in time. In this study we aim to document changing disparities in pollution-attributable health burdens over time and, for the first time, disparities in NO2attributable health impacts across the entire U.S. We show that, despite overall decreases in the public health damages associated with NO2 and PM2.5, ethnoracial relative disparities in NO2-attributable pediatric asthma and PM2.5-attributable premature mortality in the U.S. have widened during the last decade. Racial disparities in PM2.5 attributable premature mortality and NO2-attributable pediatric asthma have increased by 19% and 16%, respectively, between 2010 and 2019. Similarly, ethnic disparities in PM2.5-attributable premature mortality have increased by 40% and NO2-attributable pediatric asthma by 10%. These widening trends in air pollution disparities are reversed when more stringent air quality standard levels are met for both pollutants. Our methods provide a semi-observational approach to tracking changes in disparities in air pollution and associated health burdens across the U.S.

We investigate the relationships among summertime ozone (O 3), temperature, and humidity on daily timescales across the Northern Hemisphere using observations and model simulations. Temperature and humidity are significantly positively correlated with O 3 across continental regions in the midlatitudes (∼35-60 • N). Over the oceans, the relationships are consistently negative. For continental regions outside the midlatitudes, the O 3-meteorology correlations are mixed in strength and sign but generally weak. Over some high latitude, low latitude, and marine regions, temperature and humidity are significantly anticorrelated with O 3. Daily variations in transport patterns linked to the position and meridional movement of the jet stream drive the relationships among O 3 , temperature, and humidity. Within the latitudinal range of the jet, there is an increase (decrease) in O 3 , temperature, and humidity over land with poleward (equatorward) movement of the jet, while over the oceans poleward movement of the jet results in decreases of these fields. Beyond the latitudes where the jet traverses, the meridional movement of the jet stream has variable or negligible effects on surface-level O 3 , temperature, and humidity. The O 3-meteorology relationships are largely the product of the jet-induced changes in the surface-level meridional flow acting on the background meridional O 3 gradient. Our results underscore the importance of considering the role of the jet stream and surface-level flow for the O 3-meteorology relationships, especially in light of expected changes to these features under climate change. Plain Language Summary The relationship of ozone (O 3) with meteorological variables such as temperature and humidity at the Earth's surface varies in strength and sign. Some regions, such as continental parts of the midlatitudes, experience increases in O 3 as the temperature or humidity rises. However, this is not the case over the entire Northern Hemisphere. We use detailed computer simulations of atmospheric chemistry to show that these relationships are primarily the result of changes in meteorology, not changes in emissions or chemistry. The relationship between O 3 and meteorological variables is related to the north-south movement of the jet stream, powerful eastward-flowing air currents located near the tropopause that can encircle the hemisphere. Specifically, we find that the jet stream influences the O 3-meteorology relationships due to its effect on the northward and southward advection of O 3 , temperature, and humidity and not due to cyclones and the associated frontal activity, as has been previously suggested. Our results are relevant for understanding the present-day O 3-meteorology relationships and how climate change may impact O 3 pollution.