The spatial relationship between traffic-generated air pollution and noise in 2 US cities

Abstract

Traffic-generated air pollution and noise have both been linked to cardiovascular morbidity. Since traffic is a shared source, there is potential for correlated exposures that may lead to confounding in epidemiologic studies. As part of the Multi-Ethnic Study of Atherosclerosis and Air Pollution (MESA Air), 2-week NO and NO2 concentrations were measured at up to 105 locations, selected primarily to characterize gradients near major roads, in each of 9 US communities. We measured 5-min A-weighted equivalent continuous sound pressure levels (Leq) and ultrafine particle (UFP) counts at a subset of these NO/NO2 monitoring locations in Chicago, IL (N = 69 in December 2006; N = 36 in April 2007) and Riverside County, CA (N = 46 in April 2007). Leq and UFP were measured during non-“rush hour” periods (10:00–16:00) to maximize comparability between measurements. We evaluated roadway proximity exposure surrogates in relation to the measured levels, estimated noise–air pollution correlation coefficients, and evaluated the impact of regional-scale pollution gradients, wind direction, and roadway proximity on the correlations. Five-minute Leq measurements in December 2006 and April 2007 were highly correlated (r = 0.84), and measurements made at different times of day were similar (coefficients of variation: 0.5–13%), indicating that 5-min measurements are representative of long-term Leq. Binary and continuous roadway proximity metrics characterized Leq as well or better than NO or NO2. We found strong regional-scale gradients in NO and NO2, particularly in Chicago, but only weak regional-scale gradients in Leq and UFP. Leq was most consistently correlated with NO, but the correlations were moderate (0.20–0.60). After removing the influence of regional-scale gradients the correlations generally increased (Leq–NO: r = 0.49–0.62), and correlations downwind of major roads (Leq–NO: r = 0.53–0.74) were consistently higher than those upwind (0.35–0.65). There was not a consistent effect of roadway proximity on the correlations. In conclusion, roadway proximity variables are not unique exposure surrogates in studies of endpoints hypothesized to be related to both air pollution and noise. Moderate correlations between traffic-generated air pollution and noise suggest the possibility of confounding, which might be minimized by considering regional pollution gradients and/or prevailing wind direction(s) in epidemiologic studies.

Spatial Variation in Environmental Noise and Air Pollution in New York City

“…In a study in Chicago, IL and Riverside, CA, researchers reported moderate correlations (r=0.2-0.6, depending on location and time period) between short-term L eq (5 min) and 2-week average pollutant levels. 16 Similarly, correlations between 5-min L eq and 2-week average NO 2 were reported at 0.53 in Vancouver, BC while reported correlations between average 24-h noise and monthly NO 2 levels in Spain were 0.62. 18,19 In our study, we observed that noise NO/NO 2 correlations were more consistent with those found by Forester et al (2010), possibly due to the longer sampling time applied to characterize average noise levels.…”

“…Total kernel-weighted traffic density was the best predictor of average noise levels, followed by road density, truck traffic, and bus traffic. While prior studies have examined relationships of noise and traffic density using metrics such as inverse distance to roadways, 16 traffic density at the monitoring site, 19 or through land-use regression modeling of roadway lengths in buffers, 43 we evaluated associations with traffic intensity in varying buffer sizes to demonstrate the spatial scale of impacts, showing decreasing correlations with larger buffer sizes. We found relatively lower correlations of average noise levels with built space density, although in future multivariate models, this indicator may be useful in capturing spatial variation due to non-traffic-related noise.…”

“…15 Road traffic is a source of noise and air pollution, raising the possibility that associations between traffic exposures and cardiovascular endpoints involve possible confounding and/or synergism between noise and air pollution and their effects on health. [16][17][18][19][20] Despite the recognized need to consider noise and stress as potential confounders of air pollution effects, 15 relatively few studies of traffic impacts on health have considered noise in risk models. 17,21 Urban air pollution monitoring studies in New York City (NYC) have indicated significant spatial variation in traffic-related air pollutants, 22,23 but less data is available to characterize intraurban spatial variation in noise.…”

Metrics in Urban Health: Current Developments and Future Prospects

“…This upward trend has been facilitated by innovative new methodologies for data collection and analysis. Spatial data and mapping were the most commonly used data collection methods (2,7,11,20,24,41,53). Another major source of data has been large-scale household surveys (28,42,91).…”

Correlating transportation noise frequencies with ultrafine particulate emissions by source: Implications for environmental health studies

“…Only a few recent epidemiologic studies have controlled for both variables (Beelen et Given the presence of simultaneous exposure it is difficult to separate PM and noise-related health effects. Epidemiological studies have linked both noise and air pollution to common adverse health outcomes such as increased blood pressure and myocardial infarction, with some evidence of pulmonary function also compromised by the combined effects of air pollution and noise stress (Allen et al, 2009). In urban settings, noise and air pollution share important sources, most notably for this paper -road and rail traffic.…”