Particulate matter air pollution and diesel engine exhaust have been classified as carcinogenic for lung cancer, yet few studies have explored associations with liver cancer. We used six European adult cohorts which were recruited between 1985 and 2005, pooled within the "Effects of low-level air pollution: A study in Europe" (ELAPSE) project, and followed for the incidence of liver cancer until 2011 to 2015.The annual average exposure to nitrogen dioxide (NO 2 ), particulate matter with diameter <2.5 μm (PM 2.5 ), black carbon (BC), warm-season ozone (O 3 ), and eight elemental components of PM 2.5 (copper, iron, zinc, sulfur, nickel, vanadium, silicon, and potassium) were estimated by European-wide hybrid land-use regression models at participants' residential addresses. We analyzed the association between air pollution and liver cancer incidence by Cox proportional hazards models adjusting for potential confounders. Of 330 064 cancer-free adults at baseline, 512 developed liver cancer during a mean follow-up of 18.1 years. We observed positive linear associations between NO 2 (hazard ratio, 95% confidence interval: 1.17, 1.02-1.35 per 10 μg/m 3 ), PM 2.5 (1.12, 0.92-1.36 per 5 μg/m 3 ), and BC (1.15, 1.00-1.33 per 0.5 10 À5 /m) and liver cancer incidence. Associations with NO 2 and BC persisted in two-pollutant models with PM 2.5 . Most components of PM 2.5 were associated with the risk of liver 1888 SO ET AL.
The COVID-19 containment response policies (CRPs) had
a major impact
on air quality (AQ). These CRPs have been time-varying and location-specific.
So far, despite having numerous studies on the effect of COVID-19
lockdown on AQ, a knowledge gap remains on the association between
stringency of CRPs and AQ changes across the world, regions, nations,
and cities. Here, we show that globally across 1851 cities (each more
than 300 000 people) in 149 countries, after controlling for
the impacts of relevant covariates (e.g., meteorology), Sentinel-5P
satellite-observed nitrogen dioxide (NO
2
) levels decreased
by 4.9% (95% CI: 2.2, 7.6%) during lockdowns following stringent CRPs
compared to pre-CRPs. The NO
2
levels did not change significantly
during moderate CRPs and even increased during mild CRPs by 2.3% (95%
CI: 0.7, 4.0%), which was 6.8% (95% CI: 2.0, 12.0%) across Europe
and Central Asia, possibly due to population avoidance of public transportation
in favor of private transportation. Among 1768 cities implementing
stringent CRPs, we observed the most NO
2
reduction in more
populated and polluted cities. Our results demonstrate that AQ improved
when and where stringent COVID-19 CRPs were implemented, changed less
under moderate CRPs, and even deteriorated under mild CRPs. These
changes were location-, region-, and CRP-specific.
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