1 Particulate matter emitted through incomplete combustion of fossil fuels and biomass, known as combustion-
2 emitted particulate matter (CE-PM), has emerged as a critical public health and climate change issue in the
3 United States (US) and world-wide. Despite the implementation of The Clean Air Act in the 1970s, which led to
4 a persistent reduction in ambient PM2.5 levels in the US, racial-ethnic disparities in PM exposure remain
5 significant. People of color (POC), on average, experience disproportionate exposure to ambient PM2.5, with
6 Black Americans experiencing the highest levels of PM2.5 exposure both nation-wide (by 34% higher than White
7 Americans) and in most states. Moreover, the majority (>75%) of PM2.5 that POC breathe is from emission
8 sources disproportionately affecting POC. This pattern is consistent across exposure levels, even in POC with
9 optimal social determinants of health status (SDOH). The literature also reports that Black Americans reside
10 near emission sources such as traffic and industry due to a legacy of racist housing policies, and thus may be
11 exposed to more toxic PM, i.e., fresh combustion particles. A significant knowledge gap remains regarding
12 whether racial-ethnic disparity in ambient PM2.5 exposure can translate to higher lung deposition dose of black
13 carbon in Black versus White Americans and whether Black Americans are exposed to PM with stronger pro-
14 inflammatory potency than White Americans. We hypothesized that not only do Black Americans have higher
15 PM exposure, but that they are also exposed to more toxic PM due to the proximity of their neighborhoods to
16 traffic and industry. Macrophage carbon load (MaCL) is a novel sputum cytology-based method that quantifies
17 black carbon particles engulfed by the macrophages and reflects the lung dose of total CE-PM exposure at an
18 individual level over the past several months. We have successfully developed an innovative Machine-Learning
19 algorithm for Engulfed cArbon Particles (MacLEAP) that automates the scoring process of MaCL assay, and is
20 validated, high-throughput, and scorer-independent. This application will utilize biospecimens (sputum and blood)
21 from the Subpopulations and Intermediate Markers in COPD Study (SPIROMICS), a NHLBI-funded
22 observational study, which enrolled a geographically diverse cohort consisting predominantly of Black and White
23 Americans. We have identified 139 Black and White Americans each that are frequency-matched by age (± 10
24 years), sex (male and female), and stratum (non-smokers, smokers without airflow obstruction, smokers with
25 mild/moderate COPD, and smokers with severe COPD). Specific Aim 1 will assess whether Black Americans
26 have higher lung deposition dose of black carbon compared to White Americans using MaCL assay. Specific
27 Aim 2 will compare pro-inflammatory potency of PM exposures between Black and White Americans based on
28 slopes of the dose-response relationship between MaCL and pulmonary and systemic inflammation. Successful
29 completion of this study will greatly advance our understanding of racial-ethnic disparities in PM exposure and
30 toxicity, which is critical for identifying drivers of racial-ethnic disparities in PM induced health effects.