Table 2.

Association between single air pollutant and incident rheumatoid arthritis (RA) among UK Biobank participants ($N=$342,973; $n=$2,034 incident RA cases).

Air pollutantsa	Case/$n$	HR (95% CI) of incident RAb	$p_{\text{Trend}}$
${\mathrm{PM}}_{2.5}$
Per IQR increment	—	1.07 (1.01, 1.13)
Q1	467/86,448	Ref	0.000043
Q2	480/86,172	0.97 (0.86, 1.11)
Q3	504/84,731	1.00 (0.88, 1.14)
Q4	583/85,622	1.12 (1.00, 1.26)
${\mathrm{PM}}_{10}$
Per IQR increment	—	1.01 (0.96, 1.07)
Q1	486/86,006	Ref	0.13
Q2	511/85,457	0.99 (0.88, 1.13)
Q3	516/85,870	0.98 (0.87, 1.11)
Q4	521/85,640	1.05 (0.92, 1.19)
${\mathrm{PM}}_{2.5–10}$
Per IQR increment	—	1.00 (0.96, 1.04)
Q1	498/86,570	Ref	0.12
Q2	504/85,471	1.00 (0.88, 1.13)
Q3	499/85,500	1.00 (0.88, 1.13)
Q4	533/85,432	1.05 (0.93, 1.19)
${\mathrm{NO}}_2$
Per IQR increment	—	1.03 (0.98, 1.09)
Q1	442/85,746	Ref	0.00042
Q2	512/85,758	1.06 (0.93, 1.20)
Q3	536/85,722	1.08 (0.95, 1.23)
Q4	544/85,747	1.14 (1.00, 1.30)
${\mathrm{NO}}_{\mathrm{x}}$
Per IQR increment	—	1.07 (1.02, 1.12)
Q1	442/85,750	Ref	0.000011
Q2	498/85,758	1.05 (0.92, 1.19)
Q3	518/85,740	1.05 (0.93, 1.20)
Q4	576/85,725	1.17 (1.03, 1.33)

Note: —, not applicable; CI, confidence interval; HR, hazard ratio; IQR, interquartile range; ${\mathrm{NO}}_2$, nitrogen dioxide; ${\mathrm{NO}}_{\mathrm{x}}$, nitrogen oxides; ${\mathrm{PM}}_{2.5}$, particulate matter with aerodynamic diameter $\le 2.5\mathrm{\mu }\mathrm{m}$; ${\mathrm{PM}}_{2.5–10}$, particulate matter with an aerodynamic diameter between 2.5 and $10\mathrm{mm}$; ${\mathrm{PM}}_{10}$, particulate matter with an aerodynamic diameter $\le 10\mathrm{\mu }\mathrm{m}$; Q, quartile.

^a ${\mathrm{PM}}_{2.5}$ ranges: quartile 1: $\left(8.17–9.23\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$, quartile 2: $\left(9.24–9.88\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$, quartile 3: $\left(9.89–10.49\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$, and quartile 4: $\left(10.50–21.31\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$ and IQR is $1.26{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$; ${\mathrm{PM}}_{10}$ ranges: quartile 1: $\left(25.73–35.89\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$, quartile 2: $\left(35.90–38.01\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$, quartile 3: $\left(38.02–40.33\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$, and quartile 4: $\left(40.34–60.16\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$ and IQR is $4.44{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$; ${\mathrm{PM}}_{2.5–10}$ ranges: quartile 1: $\left(5.57–5.83\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$, quartile 2: $\left(5.84–6.08\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$, quartile 3: $\left(6.09–6.59\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$, and quartile 4: $\left(6.60–12.82\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$ and IQR is $1.26{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$; ${\mathrm{NO}}_2$ ranges: quartile 1: $\left(8.86–22.40\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$, quartile 2: $\left(22.41–27.30\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$, quartile 3: $\left(27.31–32.62\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$, and quartile 4: $\left(32.63–125.12\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$ and IQR is $10.22{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$; ${\mathrm{NO}}_{\mathrm{x}}$ ranges: quartile 1: $\left(19.74–33.38\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$, quartile 2: $\left(33.39–41.27\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$, quartile 3: $\left(41.28–49.48\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$, and quartile 4: $\left(49.49–265.94\right){\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$ and IQR is $16.10{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$.

^b Adjusted for age, sex, UK Biobank assessment center, household income, education level, smoking status, body mass index, alcohol consumption, sedentary time, physical activity duration, and healthy diet score.