Table 1.

Recent Epidemiological Studies Investigating the Association of PD and Air Pollution

Author	Study Design	Population	Exposure Range	Length of Exposure/Lag time to Ds	OR	Strengths	Weaknesses
Kirrane 201514	Case-Control	301 cases in US	O3 (ppb):  • IA mean: 39.0, max: 41.5  • NC mean 40.6, max 46.5 PM2.5 (μg/m3):  • IA mean 8.9, max 11.5  • NC mean 12.6, max 17.7	4 years	O3: OR = 1.39 (.98-1.98) PM2.5: OR = 1.34 (.93–1.93)	Adjusted for multiple variables including pesticides	Short exposure time, small population
Ritz 2016 19	Case-Control	1696 PD cases in Denmark	NO2: 9.8-43.26 ug/m3 NOx: 13.46-181.55 ug/m3 CO: 0.36-2.34 mg/m3	31 years	NO2: 1.09 per 2.97 μg/m of exposure NOx: 1.06 per 7.10 ppb of exposure CO: 1.13 per 0.12 ppm of exposure	Large population, long exposure, adjusted for multiple variables	Low air pollution in Denmark
Lee 2016 15	Case-Control	11,117 incident PD cases in Taiwan	PM10: 29.3-86.8 ug/m3 NOx: 5.2-77.6 ppb O3: 19.0-39.2 ppb CO: 0.2-1.5 ppm	11 years	CO: OR = 1.37 (1.23–1.52) Multi-pollutant models: OR = 1.17 (1.07–1.27)	Large population, adjusted for age, year of Dx	Short exposure time, adjusted for only a few variables
Lee 2016 16	Case-Control	408 incident PD cases in Denmark (subset of Ritz 2016)	NO2: 9.8-43.26 ug/m3 NOx: 13.46-181.55 ug/m3 CO: 0.36-2.34 mg/m3	31 years	AA allele of the interleukin-1β) gene with high NO exposure: OR = 3.1	Long exposure, adjusted for multiple variables, gene interaction with air pollution	Small population, low air pollution in Denmark,
Liu 2016 17	Case-Control	1,556 cases in US	Quintiles PM2.5 (μg/m3):  • Q1:4.4- < 10.8  • Q2: 10.8- < 12.3  • Q3: 12.3- < 13.8  • Q4: 13.8- < 15.4  • Q5: 15.4–26.9 PM10  • Q1:4.3- < 22.9  • Q2: 22.9- < 25.1  • Q3: 25.1- < 27.9  • Q4: 27.9- < 33.8  • Q5: 33.8–65.4 NO2 (ppb):  • Q1: 1.0- < 7.7  • Q2: 7.7- < 10.4  • Q3: 10.4- < 13.1  • Q4: 13.1- < 16.6  • Q5: 16.6–34.2	Average of 1990 and 2000, very short to no lag to disease onset.	PM2.5: OR = 1.02 per 3.8 μg/m3 PM10: OR = 1.02 per 8.4 μg/m3 NO2: OR = 1.01 per 7.3 ppb of exposure Female: PM10: Q5 vs. Q1: OR = 1.65 Never smokers: PM2.5: Q5 vs. Q1: OR = 1.29	Adjusted for multiple variables, large population. Preplanned subgroup analysis	Short exposure time, little to no lag time
Palacios 2017 18	Prospective	N =50,352 550 PD cases in US	PM2.5: 3.1-29.2 ug/m3 PM10: 7.4-81.3 ug/m3	9 years	0.99 (0.96-1.01)	Prospective, Adjusted for age, tobacco	Short exposure time to disease.
Chen 2017 13	Case-Control	1060 incident PD cases in Taiwan	PM10 Tertiles (μg/m3):  • T1 ≤ 54  • 54 < T2 ≤ 65  • T3 > 65 SO2, O3, CO, NOx, NO, NO2, THC, CH4, and NMHC not specified.	1-18 years	PM10 T3 v T1: OR = 1.35 (1.12-1.62) Others increased only with comorbidity	Large population of incident cases. Considered comorbid conditions.	Variable exposure and lag time. Did not have data on PM2.5. Adjusted for age and gender only.
Shin 2018 21	Population-based cohort	38 745 incident cases in Ontario, Canada	PM2.5: 1.3-20.0 ug/m3 NO2: 2.2-53.2 ppb O3: 24.3-64.1 ppb	2, 5 and 10 year lag.	PM2.5: 4% increase risk per interquartile increment of 3.8 ug/m3 Similar results for NO2 and O3.	Large population, Considered comorbid conditions.	Relatively short exposure lag, did not adjust for smoking, physical activity or pesticide exposure.
Cerza 2018 12	Prospective cohort	13,104 cases in Rome, Italy	PM2.5: 9.8-31.4 ug/m3 PM10: 29.6-58.2 ug/m3 NO2: 13.2-84.9 ug/m3 NOx: 14.3-173.4 ug/m3 O3: 54.5-112.8 ug/m3	0-3 year lag	PM abs, NO2: HR = 0.97 per 10 μg/m3 increase NOx: HR = 0.97 per 20 μg/m3 increase O3: HR = 1.02 per 10 μg/m3 increase	Large prospective study. Adjusted for gender and age	Short to no lag time, Did not adjust for other exposures, occupation, limited adjustment for smoking.
Salimi 2019 20	Cross sectional	1,428 cases in New South Wales, Australia	PM2.5: 0.1-10.3 ug/m3 NO2: 4.21-71.2 ug/m3	0-2 year lag	PM2.5: OR = 1.01 per 1 ug/m3 NO2: OR = 1.03 (all) and 1.11 (past smokers) per 5 ug/m3	Adjusted for multiple potential confounds including smoking	Short to no lag time, Self-reported cases. Limited statistical power. Relatively low range PM2.5 range.
Yuchi 2020 22	Database Cohort	4,201 cases in Vancouver, Canada	PM2.5: 0.1-10.4 ug/m3 NO2: 12-57.7 ppb NO: 8.2-101.0 ppb	5-9 years	PM2.5: HR = 1.09 per interquartile range (IQR) NO2: HR = 1.12 per IQR NO: HR = 1.03 per IQR	Large number of cases. Multiple co-variants reported.	Relatively low range PM2.5 range. Did not adjust for smoking or other behavioral risks.
Jo 2021 10	Retrospective cohort study	338 newly diagnosed cases in South Korea	PM2.5: 18.0-44.4 ug/m3 PM10: 41.0-79.0 NO2: 0.026-0.045 ppm O3: 0.013-0.025 ppm SO2: 0.0036-0.0074 ppm CO: 0.40-0.82 ppm.	5 years	NO2: HR = 1.41 highest v lowest quartile. No significance for other measures	Measured several pollution components, Adjusted for multiple co-variants.	Low number of cases. Relatively low range PM2.5 and PM10 range. Short lag.