Background In recent years, research about effects of gaseous air pollutants on population health has continued to make progress, but evidence for the impacts on peripheral hematology is still limited.

Objective This study is designed to investigate the effects of exposures to main gaseous air pollutantscarbon monoxide (CO), nitrogen dioxide (NO₂), ozone (O₃), and sulfur dioxide (SO₂) on blood routine indicators of elderly residents.

Methods From January 2018 to September 2019, blood routine tests, basic information surveys, and environmental exposure data collection were performed on 427 people aged 50 to 78 years in a community of Beijing. Univariate linear regression models were used to explore the potential risk factors of blood routine indicators. Single-pollutant multivariate linear regression models were established to analyze the effects of gaseous pollutants on blood routine indicators. Effect modification models and two-pollutant multivariate linear regression models were conducted to explore the robustness of the results from the single-pollutant models.

Results The mediansinterquartile ranges (IQR) of white blood cells, red blood cells, and platelets of the study subjects were 5.7×10⁹(1.7×10⁹), 4.6×10¹²(0.5×10¹²), and 217.0×10⁹(63.5×10⁹) L^-1, respectively. Along with the increases in SO₂, neutrophils percentage showed significant decreases (P < 0.05), while lymphocytes percentage showed significant increases (P < 0.05). Red blood cells counts, mean corpuscular hemoglobin and its concentration showed significant decreases (P < 0.05), whereas mean corpuscular volume and red cell distribution width standard deviation showed significant increases (P < 0.05) along with increases of the four pollutants. An IQR increment in CO (0.4 mg·m^-3), NO₂ (24.4 μg·m^-3), O₃ (67.1 μg·m^-3), and SO₂ (3.4 μg·m^-3) at 90-d moving average was significantly associated with percent changes of -2.6% (95% CI:-3.7%--1.4%), -2.6% (95% CI:-4.0%--1.2%), -3.2% (95% CI:-4.8%--1.5%), and -2.9% (95% CI:-3.9%--1.9%) (all P < 0.01) in mean corpuscular hemoglobin concentration, respectively. Along with the increases in CO, NO₂, and SO₂, platelet count, mean platelet volume, and platelet hematocrit showed decreasing trends (P < 0.05), while platelet distribution width showed an increasing trend (P < 0.05). An IQR increment in CO, NO₂, and SO₂ at 90-d moving average was significantly associated with percent changes of -21.2% (95% CI:-29.3%--12.2%), -19.7% (95% CI:-29.3%--8.8%), and -15.6% (95% CI:-23.2%--7.2%) (all P < 0.01) in platelet hematocrit, respectively. No significant effect modification was observed when the data were stratified by cold, passive smoking, chronic diseases such as hypertension and diabetes, and medication use (P ≥ 0.10). The results of the two-pollutant models controlling for other gaseous air pollutants and fine particulate matters at the same time window were generally consistent with those of the single-pollutant models.

Conclusion Exposure to gaseous air pollutants may lead to quantitative and morphological changes in white blood cells, red blood cells, and platelets.