Investigating the Urban Air Quality Effects of Cool Walls and Cool Roofs in Southern California.

Solar reflective cool roofs and walls can be used to mitigate the urban heat island effect. While many past studies have investigated the climate impacts of adopting cool surfaces, few studies have investigated their effects on air pollution, especially on particulate matter (PM). This research for the first time investigates the influence of widespread deployment of cool walls on urban air pollutant concentrations, and systematically compares cool wall to cool roof effects. Simulations using a coupled meteorology-chemistry model (WRF-Chem) for a representative summertime period show that cool walls and roofs can reduce urban air temperatures, wind speeds, and planetary boundary heights in the Los Angeles Basin. Consequently, increasing wall (roof) albedo by 0.80, an upper bound scenario, leads to maximum daily 8-h average ozone concentration reductions of 0.35 (0.83) ppbv in Los Angeles County. However, cool walls (roofs) increase daily average PM2.5 concentrations by 0.62 (0.85) µg m-3. We investigate the competing processes driving changes in concentrations of speciated PM2.5. Increases in primary PM (elemental carbon and primary organic aerosols) concentrations can be attributed to reductions in ventilation of the Los Angeles Basin. Increases in concentrations of semivolatile species (e.g., nitrate) are mainly driven by increases in gas-to-particle conversion due to reduced atmospheric temperatures.

Systematic Comparison of the Influence of Cool Wall versus Cool Roof Adoption on Urban Climate in the Los Angeles Basin.

This study for the first time assesses the influence of employing solar reflective "cool" walls on the urban energy budget and summertime climate of the Los Angeles basin. We systematically compare the effects of cool walls to cool roofs, a heat mitigation strategy that has been widely studied and employed, using a consistent modeling framework (the Weather Research and Forecasting model). Adoption of cool walls leads to increases in urban grid cell albedo that peak in the early morning and late afternoon, when the ratio of solar radiation onto vertical walls versus horizontal surfaces is at a maximum. In Los Angeles County, daily average increase in grid cell reflected solar radiation from increasing wall albedo by 0.80 is 9.1 W m-2, 43% of that for increasing roof albedo. Cool walls reduce canyon air temperatures in Los Angeles by 0.43 K (daily average), with the peak reduction (0.64 K) occurring at 09:00 LST and a secondary peak (0.53 K) at 18:00 LST. Per 0.10 wall (roof) albedo increase, cool walls (roofs) can reduce summertime daily average canyon air temperature by 0.05 K (0.06 K). Results reported here can be used to inform policies on urban heat island mitigation or climate change adaptation.

Unified real-time environmental-epidemiological data for multiscale modeling of the COVID-19 pandemic.

An impressive number of COVID-19 data catalogs exist. However, none are fully optimized for data science applications. Inconsistent naming and data conventions, uneven quality control, and lack of alignment between disease data and potential predictors pose barriers to robust modeling and analysis. To address this gap, we generated a unified dataset that integrates and implements quality checks of the data from numerous leading sources of COVID-19 epidemiological and environmental data. We use a globally consistent hierarchy of administrative units to facilitate analysis within and across countries. The dataset applies this unified hierarchy to align COVID-19 epidemiological data with a number of other data types relevant to understanding and predicting COVID-19 risk, including hydrometeorological data, air quality, information on COVID-19 control policies, vaccine data, and key demographic characteristics.

Long-term trends in urban NO2 concentrations and associated paediatric asthma incidence: estimates from global datasets.

BACKGROUND: Combustion-related nitrogen dioxide (NO2) air pollution is associated with paediatric asthma incidence. We aimed to estimate global surface NO2 concentrations consistent with the Global Burden of Disease study for 1990-2019 at a 1 km resolution, and the concentrations and attributable paediatric asthma incidence trends in 13 189 cities from 2000 to 2019. METHODS: We scaled an existing annual average NO2 concentration dataset for 2010-12 from a land use regression model (based on 5220 NO2 monitors in 58 countries and land use variables) to other years using NO2 column densities from satellite and reanalysis datasets. We applied these concentrations in an epidemiologically derived concentration-response function with population and baseline asthma rates to estimate NO2-attributable paediatric asthma incidence. FINDINGS: We estimated that 1·85 million (95% uncertainty interval [UI] 0·93-2·80 million) new paediatric asthma cases were attributable to NO2 globally in 2019, two thirds of which occurred in urban areas (1·22 million cases; 95% UI 0·60-1·8 million). The proportion of paediatric asthma incidence that is attributable to NO2 in urban areas declined from 19·8% (1·22 million attributable cases of 6·14 million total cases) in 2000 to 16·0% (1·24 million attributable cases of 7·73 million total cases) in 2019. Urban attributable fractions dropped in high-income countries (-41%), Latin America and the Caribbean (-16%), central Europe, eastern Europe, and central Asia (-13%), and southeast Asia, east Asia, and Oceania (-6%), and rose in south Asia (+23%), sub-Saharan Africa (+11%), and north Africa and the Middle East (+5%). The contribution of NO2 concentrations, paediatric population size, and asthma incidence rates to the change in NO2-attributable paediatric asthma incidence differed regionally. INTERPRETATION: Despite improvements in some regions, combustion-related NO2 pollution continues to be an important contributor to paediatric asthma incidence globally, particularly in cities. Mitigating air pollution should be a crucial element of public health strategies for children. FUNDING: Health Effects Institute, NASA.

Global urban temporal trends in fine particulate matter (PM2·5) and attributable health burdens: estimates from global datasets.

BACKGROUND: With much of the world's population residing in urban areas, an understanding of air pollution exposures at the city level can inform mitigation approaches. Previous studies of global urban air pollution have not considered trends in air pollutant concentrations nor corresponding attributable mortality burdens. We aimed to estimate trends in fine particulate matter (PM2·5) concentrations and associated mortality for cities globally. METHODS: We use high-resolution annual average PM2·5 concentrations, epidemiologically derived concentration response functions, and country-level baseline disease rates to estimate population-weighted PM2·5 concentrations and attributable cause-specific mortality in 13 160 urban centres between the years 2000 and 2019. FINDINGS: Although regional averages of urban PM2·5 concentrations decreased between the years 2000 and 2019, we found considerable heterogeneity in trends of PM2·5 concentrations between urban areas. Approximately 86% (2·5 billion inhabitants) of urban inhabitants lived in urban areas that exceeded WHO's 2005 guideline annual average PM2·5 (10 µg/m3), resulting in an excess of 1·8 million (95% CI 1·34 million-2·3 million) deaths in 2019. Regional averages of PM2·5-attributable deaths increased in all regions except for Europe and the Americas, driven by changes in population numbers, age structures, and disease rates. In some cities, PM2·5-attributable mortality increased despite decreases in PM2·5 concentrations, resulting from shifting age distributions and rates of non-communicable disease. INTERPRETATION: Our study showed that, between the years 2000 and 2019, most of the world's urban population lived in areas with unhealthy levels of PM2·5, leading to substantial contributions to non-communicable disease burdens. Our results highlight that avoiding the large public health burden from urban PM2·5 will require strategies that reduce exposure through emissions mitigation, as well as strategies that reduce vulnerability to PM2·5 by improving overall public health. FUNDING: NASA, Wellcome Trust.

TROPOMI NO2 in the United States: A Detailed Look at the Annual Averages, Weekly Cycles, Effects of Temperature, and Correlation With Surface NO2 Concentrations.

Observing the spatial heterogeneities of NO2 air pollution is an important first step in quantifying NOX emissions and exposures. This study investigates the capabilities of the Tropospheric Monitoring Instrument (TROPOMI) in observing the spatial and temporal patterns of NO2 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 NO2 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 NO2 column amounts and find that NO2 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 NO2 with increasing temperature at moderate temperatures. Finally, we demonstrate that a linear regression fit of 2019 annual TROPOMI NO2 data to annual surface-level concentrations yields relatively strong correlation (R 2 = 0.66). These new developments make TROPOMI NO2 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.

Air pollution in a microclimate; the impact of different green barriers on the dispersion.

This paper studies the impact of different green barriers on the dispersion of air pollution in a neighbourhood. The study was performed with reference to air quality conditions in Manchester, UK. Manchester experiences a high level of NO2. Measured results showed that the average annual concentration level in 2018 was very close to the limit defined by European Union legislation. Maximum and minimum NO2 concentrations occurred during the winter and summer, respectively. Simulations of the dispersion of air pollution in a hypothetical neighbourhood showed that NO2 level was decreased by the increase of air temperature during the simulated day. In four perturbation scenarios, hedges and trees with different heights were added to the neighbourhood as green barriers. Hedges increased the pollution level near the street at the pedestrian level as a result of the reduced wind speed. The simulations demonstrated that using the trees facilitated the dispersion of pollution.

Using Satellites to Track Indicators of Global Air Pollution and Climate Change Impacts: Lessons Learned From a NASA-Supported Science-Stakeholder Collaborative.

The 2018 NASA Health and Air Quality Applied Science Team (HAQAST) "Indicators" Tiger Team collaboration between NASA-supported scientists and civil society stakeholders aimed to develop satellite-derived global air pollution and climate indicators. This Commentary shares our experience and lessons learned. Together, the team developed methods to track wildfires, dust storms, pollen counts, urban green space, nitrogen dioxide concentrations and asthma burdens, tropospheric ozone concentrations, and urban particulate matter mortality. Participatory knowledge production can lead to more actionable information but requires time, flexibility, and continuous engagement. Ground measurements are still needed for ground truthing, and sustained collaboration over time remains a challenge.