On the basis of previous observations that: (1) both the nickel (Ni) concentration in ambient air fine particulate matter (PM2.5) and daily mortality rates in New York City (NYC) were much higher than in any other US city; and (2) that peaks in Ni concentration was strongly associated with cardiac function in a mouse model of atherosclerosis, we initiated a study of the spatial and seasonal distributions of Ni in NYC and vicinity to determine the feasibility of productive human population-based studies of the extent to which ambient fine particle Ni may account for cardiovascular health effects. Using available speciation data from previous studies at The New York University, Environmental Protection Agency's Speciation Trends Network; and the Interagency Monitoring of Protected Visual Environments network, we determined that Ni in NYC is on average 2.5 times higher in winter than in summer. This apparent seasonal gradient is absent, or much less pronounced, at NJ and CT speciation sites. Ni concentrations at a site on the east side of Manhattan and at two sites in the western portion of the Bronx were a factor of two higher than at a site on the west side of Manhattan, or at one at Queens College in eastern Queens County, indicating a strong spatial gradient within NYC. We conclude that the winter peaks of fine particle Ni indicate that space heating, which involves the widespread reliance on residual oil combustion in many older residential and commercial buildings in NYC, is a major source of ambient air Ni. Epidemiologic studies based on data generated by a network of speciation sites throughout NYC could effectively test the hypothesis that Ni could account for a significant portion of the excess mortality and morbidity that have been associated with elevated mass concentrations of PM2.5.
During the course of a 6-month series of 6 h/day, 5 days/week exposures of ApoE−/− mice to concentrated ambient air fine particulate matter in Tuxedo, NY (Lippmann et al., 2006), there were 14 days in which the mice exhibited highly significant increases in heart rate (HR) and decreases in HR variability. These 14 days were characterized as having much higher than average concentrations of nickel (Ni), chromium, and iron, but much lower than normal concentrations of fine particles (PM2.5), sulfur (S), aluminum (Al), and vanadium (V). The observed cardiovascular health effects were significantly associated with in vivo exposure to fine particle Ni. Back trajectory analyses for these 14 days led to the vicinity of the largest Ni smelter in North America at Sudbury, Ontario. In the same paper, Lippmann et al. (2006) regressed the daily average mortality coefficient against PM2.5 and its chemical component concentrations reported for 2000–2003 by the United States (US) Environmental Protection Agency (EPA) Speciation Trends Network (STN) for the 60 US cities with such data among the 90 cities in the National Mortality and Morbidity Study (NMMAPS; Dominici et al., 2003). In the Lippmann et al. (2006) analysis, only Ni and V were significantly associated with the significantly higher daily mortality in New York City (NYC) than in other US cities. They also noted that: (1) a study of an intervention in Hong Kong requiring the use of low S fuel in power plants on 1 July 1990 led to a prompt and sustained reduction in monthly mortality, and that the only measured pollutants that had coincident drops in airborne concentrations were S, Ni, and V (Hedley et al., 2002; Hedley et al., 2004), and (2) that the PM10 mortality coefficient for NYC in the NMMAPS study reanalysis was 3.8 times higher than the national average. The Ni was 9.5 times higher than in the average for 60 NMMAPS with speciation data for 2000–2003.
Dominici et al. (2007) extended the regression analyses of NMMAPS mortality and STN composition data out to 2005 for 69 US communities, and reported that their results were consistent with those of Lippmann et al. (2006), but that when the NYC data were excluded from their analysis, the overall associations of mortality coefficient with Ni and V were no longer statistically significant.
A variety of fuel oils are used in New York State for industrial, energy production, transportation, and space heating purposes. These fuels include both distillate and residual oils. Distillate fuel oils are distillation products of the refining process, and are typically viscous liquids that can be easily burned. Examples of distillate fuel oils include nos. 1 and 2 fuel oils, diesel fuel, and kerosene (EIA, 2007). Residual fuel oils are the residual byproducts of refined crude oil. Residual fuel oils, such as nos. 5 and 6 fuel oil (also known as bunker fuel or navy special), are generally less expensive than distillate fuels. Because they are highly viscous, residual oils usually require special equipment to heat the oil prior to combustion, or must be blended with distillate (resulting in a product that is defined as no. 4 oil), and thus are generally not suitable for use by individual consumers.
Many of the contaminants associated with crude oil are more likely to be found in lower concentrations in lighter fuel oil distillation products (e.g. nos. 1, 2, and 3 fuel oils). In contrast, the residual oil fractions (e.g. nos. 5 and 6) contain significantly more of the contaminants that were in the crude oil, and can include substantial amounts of trace metals and S. In a report by the National Research Council (NRC, 1985), no. 6 fuel oil was observed to have 89 parts per million (p.p.m.) of Ni and 73 p.p.m. of V. This contrasts with no. 2 fuel oil, which had just 0.5 p.p.m. of Ni and 1.5 p.p.m. of V. In an emissions factor study by the USEPA, residual oil combustion accounted for nearly 200 times greater Ni emission compared to distillate fuel combustion on a per unit energy basis (563 lbs Ni per 1012 Btu compared with 3 lbs Ni per 1012 Btu, respectively; USEPA, 1995). It should be noted that the confidence in these emissions factors are somewhat low, because there is some variability in contaminant concentrations due to different sources of crude oil, refinery techniques, and target levels of contaminant removal, facility used in distillation, and in storage and transportation. In any case, the absolute concentration for each fuel type is not as important as the fact that residual oils tend to have much higher contaminant loadings than distillate products. Historically, decreases in anthropogenic emissions have resulted in significant decreases in ambient Ni and V (USEPA, 1977). In the early 1970s, regulatory action reduced the S content of residual fuel oil in the NYC region, which also resulted in a ∼70% to 80% decrease in ambient V in NYC. A similar decrease was observed across the northeastern United States. Ambient Ni concentration in the northeastern US also decreased, but not as substantially as that for V.
Figure 1 shows the mean fraction of fuel consumption by sector for New York State and New Jersey from 1999 to 2006. New Jersey is comparable to New York State in that both have similar climates, large populations, active shipping ports, and commonly use fuel oils for space heating. Residual and distillate fuel oil (including no. 4 fuel oil) are presented separately in Figure 1.
Approximately 30% of residual oil (Figure 1a) in New York State is consumed by the commercial sector, which includes space heating for apartment buildings and other commercial facilities, such as office buildings and retail establishments. Using data from the Petroleum Infrastructure Study Final Report (NYSERDA, 2006), we estimate that NYC consumes at least 40% of the residual oil in New York State. In New Jersey (Figure 1b), commercial uses of residual oil are much lower than in New York, and much less is used for commercial heating. Residual oil is rarely used for heating by homeowners, and is thus not reported. Vessel bunkering constitutes the majority of residual oil consumption in New Jersey, presumably at the large shipping facilities at Port Elizabeth and Port Newark to the west of NYC. Thus, with the predominant winds into NYC coming from the west and southwest, the port facilities may represent an important source of airborne fine Ni and V throughout the year within NYC.
Residential consumption of distillate fuels for heating purposes comprises large fractions in both New York (Figure 1c) and New Jersey (Figure 1d). The largest fraction of distillate fuel use has been for highway purposes (e.g. on-road combustion of diesel fuel) in New Jersey, and may be linked to shipping and freight associated with the two major ports. The commercial sector accounts for just 8% of distillate fuel oil use in New Jersey, compared to nearly 21% of distillate fuel use in New York. This may indicate that commercial facilities (which include apartment buildings) in NYC use a significantly higher fraction of distillate fuel for heating.
As residual fuel oils are generally used only by facilities equipped with specialty burner systems, it is unlikely that most commercial apartment buildings can use unmodified residual fuels. One possibility that may account for the increased residual oil use by the commercial sector in NYC is the blending of residual oils with distillate oils into no. 4 fuel oil by local retailers and wholesalers. This enables apartment buildings and other commercial facilities to increase the consumption of both residual and distillate fuels in NYC, which is consistent with the data presented in Figure 1.
In this paper, we report on a preliminary examination of the extent of the elevated concentrations of Ni and V, and their spatial and seasonal variability, within the NYC region. Ni and V are co-emitted during combustion of fuel oils, and therefore, we discuss fine particle Ni concentration, as well as the ratio of Ni to V. As residual fuel combustion effluent from residential and commercial buildings is enriched with fine particle Ni (relative to V), it is suggested that the observed Ni is mainly a result of residual fuel combustion in such buildings. Thus, an increase in the Ni/V ratio provides evidence for residual fuel combustion aerosol. This evidence does not exclude the possibility of other point sources of Ni, though these point sources (if any) would have to be specific to NYC and would also have to be observed mainly in the winter heating season. These two metals are of particular interest because they are emitted in relatively high concentrations when residual oil is burned, and because residual oil fly ash has been used in toxicology studies as a particularly toxic particulate matter (PM) mixture (Ghio et al., 2002; Costa et al., 2006).
Speciation Data Resources
Data were collected from a number of sources, which included national regulatory network sites and sample sites operated by The New York University (NYU). Sample site information, including location, operational date ranges, and specific networks, is summarized in Table 1. The data are now further described.
Personal Exposure Study: NYU Personal Exposure Study measured PM mass and fine PM components outside of nine apartments in Manhattan, and at a Central Monitoring site on the eighth floor of the NYC Public Health Laboratory at E. 26th Street and First Avenue during 12 consecutive days in the winter and 12 days in the summer (2000–2001). This work was part of a doctoral dissertation by S.I Hsu (in preparation, 2008) Hsu (2008), a signatory coauthor of this work. Chemical composition of fine aerosol was measured at several locations, and included Ni and V mass fractions, and total fine particle mass. Ambient air was sampled with a diaphragm pump (Air Diagnostics and Engineering Inc., Harrison, ME, USA) that drew air at a mass-flow-controlled nominal rate of 10.0 l/min. Flow rate was verified daily using a rotometer. A Harvard Impactor (Air Diagnostics and Engineering Inc.) was installed inline to restrict collected aerosol to the fine particle fraction (less than 2.5 μm aerodynamic diameter). The particles were then collected on a 37 mm (Teflo, Gelman Sciences, Ann Arbor, MI, USA) polytetrafluoroethylene ringed filter, which was suspended in a conductive sampler cassette. Each sample was collected for 24 h. Prior to deployment, the filters were conditioned for at least 48 h at 22°C and relative humidity of ∼35%, and weighed using a calibrated mass balance (Mettler-Toledo, Model MT-5, Hightown, NJ, USA).
After the samples were collected, the filters were retrieved from the samplers and returned to the laboratory where they were again conditioned for at least 48 h at 22°C and relative humidity of ∼35%, and re-weighed for gravimetric analysis. The filters were then analyzed by X-ray emission Fluorescence (model EX-6600–AF; Jordan Valley, Austin, TX, USA) and processed with spectral software (XRF2000v3.1, USEPA and ManTech Environmental Technology Inc., Research Triangle Park, NC, USA) for ∼38 different transition metal elements, and included V and Ni. The method is consistent with that reported by Maciejczyk and Chen (2005).
Study of New York City and Upwind Air Quality: Daily 24-h measurements of PM mass and fine PM components were made for 3 years (2001–2003) on 37 mm Teflo filters collected on a second floor rooftop of the Hunter College School of Health Sciences at E. 25th Street and First Avenue, and simultaneously outside NYU's A.J. Lanza Laboratory in Sterling Forest, Tuxedo, NY, USA (Lall and Thurston, 2006; Lall, 2008). The samples were collected by a daily sequential sampler attachment to a TEOM Sampler with a fine particle inlet (Thermo Scientific, Model 1400ab, Raenssalear, NY, USA). The analyses of these filters were made using the same protocols described above for the filters used in the NYU Personal Exposure Study.
The Speciated Trends Network (STN) was established by the EPA as a companion to the mass-based Federal Reference Method (FRM). Data are used to establish a better understanding of chemical composition trends of fine particle aerosol. Sites (54) are located throughout urban regions of the United States, and the network has operated continuously since 1999.
Speciation Trends Network samples are 24-h integrated measurements, collected from midnight to midnight every third day (USEPA, 1997). Ambient air is sampled by a vacuum pump and aerosol is size-selected to collect particles with diameters less than 2.5 mm. This technique is comparable with the EPA FRM method. Sample is collected on two-stage filter pack that contains a 46.2 mm polytetrafluoroethylene (PFTE) and nylon filters. The nylon filter is used to capture semivolatile material that evaporates from the PFTE filter. The PFTE filter is analyzed for Ni and V (and other elements) by X-ray excitation fluorescence by EPA-approved contractors, and follows the method described in the Quality Assurance Project Plan for the field operations involved in the PM2.5 STN (USEPA, 1997).
The Interagency Monitoring of Protected Visual Environments (IMPROVE) is comprised of ∼150 sampling sites across the United States. The intent of the program is to understand how chemical composition of aerosol affects visibility in the environment, as mandated by the Clean Air Act (USEPA, 1990). Almost all IMPROVE sites are located in non-urban background locations, mostly in class I wilderness areas.
The IMPROVE sampling methods are somewhat similar to the STN measurements. Ambient air is passed through a sharp-cut cyclone that selects particle size to less than 2.5 μm. The sample is collected in a filter stack, which includes an array of nylon, quartz, and Teflon filter media. Samples are collected every third day. Filters are analyzed by an EPA-approved laboratory. The Teflon filter is analyzed by X-ray fluorescence for fine particle Ni and by particle-induced X-ray emission for fine particle V. Sample collection and analytical methods follow the published standard operating procedure (USEPA, 1997) and available online at http://vista.cira.colostate.edu/improve/publications/SOPs/ucdsop.asp.
Data Processing and Presentation
Spatial and Seasonal Distributions of Ni and V in NYC and Vicinity
The sites in NYC and vicinity for which we had access to PM2.5 speciation data are depicted in Figure 2.
Concentration data were assembled for Ni and V that we measured at the Hunter College site on First Avenue in Manhattan and at our laboratory in Sterling Forest (Tuxedo, NY, USA). We also acquired measurements made at EPA's STN sites within NYC and adjacent areas, as well as comparable data from the IMPROVE network that is focused on non-urban sites. Figure 3 shows summary data for Hunter College, and those for the CMS and for outdoors of the apartments in the Personal Exposure Study, as well as the STN sites in NYC. Figure 4 shows comparable data for sites to the west of NYC. Figure 5 shows comparable data for sites to the east of NYC. A distinct seasonal profile of Ni aerosol concentration was observed across all monitors located within NYC boundaries, as shown in Figure 3. It is notable that the measurements made on filters collected across First Avenue from the CMS at Hunter College (a second floor rooftop of Hunter College School of Health Sciences at E. 25th Street and First Avenue in Manhattan) in the period beginning as the Personal Exposure Study (cited above) were ending and were qualitatively similar. During the heating season (shaded regions), smoothed Ni FPM is significantly enhanced compared with the non-heating season. The winter season is defined at 1st October–31st March of each year, and the summer season consists of 1st April–30th September of each year. This roughly coincides with NYC housing regulations that mandate the availability of residential space heating under certain weather conditions from 1st October–31st May. The magnitudes and seasonal patterns of the Ni concentration measurements made at Hunter College, and at IS no. 52 and the Bronx botanical garden in the Bronx, were also similar, whereas those measured at Queens College and at Canal Street on the lower west side, were considerably smaller. Also, for all of these sites, the Ni/V ratios were much higher than 1.
In comparison to the findings from NYC, it can also be seen that the magnitudes and seasonal patterns of all of the measurements made to the west of NYC in Sterling Forest and in NJ were much lower, with the Ni concentrations being considerably lower, and the Ni/V ratios all being near 1 (Figure 4). The highest Ni concentrations in this region were in Elizabeth, which is close to NYC and to the Port of New York facilities, in Trenton and Camden, which are close to Philadelphia, and in Sterling Forest. The most pronounced peaks in Sterling Forest may have been due to long-range transport from the Sudbury, Ontario Ni smelter, as reported in our previous paper (Lippmann et al., 2006). Furthermore, FPM Ni concentrations were lowest at regional background sites (Chester in northwest NJ, and at Brigantine, a seaside resort town in southeast NJ) and provides additional evidence for relatively localized sources of Ni and V aerosol in NYC.
It should be noted that even in the non-heating season, ambient concentration of FPM Ni in NYC is consistently higher than surrounding regions. Mean summer concentrations at NYC sites range from ∼7 to 17 ng/m3 at NYC sites, which are compared with ∼1 to 8 ng/m3 at the CT and NJ sites (see Table 2). There are a number of possible explanations for this finding, but is most likely caused by a combination of upwind vessel bunkering emissions from the two large shipping ports in New Jersey and possibly some contribution from commercial/residential residual fuel combustion. Apartment buildings in NYC typically produce domestic hot water using the large boilers used for winter space heating. As domestic hot water use probably does not have a seasonal profile, residual oil combustion occurs, therefore, throughout the year. To a lesser extent, transient ship traffic in the nearby Hudson and East Rivers may also contribute some fraction to the observed ambient FPM Ni.
Finally, as depicted in Figure 5, the magnitudes and seasonal pattern in Ni concentration measurements made in Mohawk Mountain in northwestern CT were much lower than those in NYC (∼1 ng/m3), with the Ni/V ratios were near 1. At the Westport and New Haven locations, which are frequently downwind of NYC, the Ni concentrations were higher, with some slight peaking in the heating season. However, the seasonal variability that was observed in NYC was less in these downwind locations.
The results plotted in Figures 3, 4 and 5 are summarized in Table 2. It can be seen that the heating season increment in Ni concentration at the speciation sites in Manhattan, Bronx and Queens range from ∼10 to 30 ng/m3, whereas those at sites outside of NYC are below 1 ng/m3, except for Camden, NJ, at 1.3, and New Haven, CT, at 2.3 ng/m3. These two sites, as well as those at Elizabeth and Brigantine NJ, were the only ones where the average V concentrations were higher than those of Ni.
Ni concentrations on the east side of Manhattan (Hunter College, NYU central Monitor, and NYU Home Study) and at the two Bronx STN sites (IS52 and Bronx botanical gardens) were, on average, a factor of two higher than those at the STN sites at Queens College and Canal Street (on the western edge of Manhattan), which in turn were much higher than those in adjacent areas outside of NYC. The higher Ni concentrations on the east side of Manhattan and in the Bronx during the heating season appear to be attributable to large commercial and residential space heating sources burning residual fuel oil. Also, as shown in Table 2, there are higher Ni/V ratios in the heating season, suggesting that fuel oil used for space heating contains much more Ni than V. By contrast, the power plant and shipboard combustion sources that are dominant outside the areas of those parts of NYC with numerous high-rise buildings appear to produce a lower and more uniform regional concentration background with Ni/V ratios closer to one. Thus, combustion of residual oil for space heating in large commercial and residential buildings appears to cause large spatial gradients in Ni concentrations within NYC during the heating season.
Correlation coefficients were calculated for measured fine particle Ni at each location used in this study and are presented in a correlation coefficient matrix in Table 3. Very poor agreement of fine particle Ni concentration was observed across most of the locations with just ∼8% of sites having r-values (absolute value) >0.500. This suggests considerable spatial variability of fine particle Ni in the NYC metropolitan area. The sites in closest agreement were the two sites located in the Bronx (IS52); however, this was expected as they are colocated. Queens College and Bronx botanical garden were also in agreement with one another (r=0.535). Three background locations—Westport and Mohawk Mountain, and Westport and Chester, NJ—were correlated with one another (Table 3), and may indicate a regional background signal of fine particle Ni. Interestingly, the New Haven STN location (but not the IMPROVE colocated measurements) were in agreement with the Bronx STN location (IS52), and Queens Community College—both locations in NYC (∼100 km to the southwest). The correlation was not observed with the colocated IMPROVE measurements in New Haven that operated at the same location before the STN site was functional (prior to February 2004). This relationship is unclear and warrants further investigation.
Large spatial and seasonal variations of fine particle Ni are observed through the NYC metropolitan region. It has also been shown that there is large spatial and seasonal variability within NYC itself, which is suggested by observations at the three NYC speciation monitors. However, the absence of data from Kings County (Brooklyn), Richmond County (Staten Island), and the eastern portions of the Bronx and Queens Counties prevents a quantitative evaluation of the extent of the variations within NYC, especially for the more than half of the NYC population in these uncharacterized areas. Given the very large population in NYC (∼8.2 million), and the extensive spatial and seasonal variations in airborne NYC Ni, definitive studies of the health consequences of the inhalation of ambient air Ni should be possible and practical as soon as measurement data on ambient air levels at representative sites within the five NYC Boroughs become available. The hypothesis that no. 4 fuel oil, which is widely used in large commercial and residential buildings, has a much higher Ni/V ratio needs further examination.
Ni concentrations on the east side of Manhattan and at the two Bronx sites were much higher than those at Queens College and those at Canal Street on the western edge of Manhattan, which in turn were much higher than those in adjacent areas outside of NYC. The higher Ni concentrations in Manhattan and Bronx during the heating season appear to be attributable to space heating sources. Also, as shown in Table 2, there are higher Ni/V ratios in the heating season, suggesting that residual fuel oil used for space heating contains much more Ni than V. By contrast, the power plant and shipboard combustion sources that are dominant outside the areas of those parts of NYC with numerous high-rise buildings appear to produce a lower and more uniform regional concentration background with Ni/V ratios closer to one. Thus, combustion of residual oil in residential and commercial buildings may cause large spatial gradients in Ni concentrations within NYC during the heating season.
This research was supported, in part, by a Cooperative Agreement from the USEPA (CR 827164), by a Center grant from the USEPA (R 827351), by a post-doctoral training grant for Dr. Peltier from NIEHS (ES 007324), by research grants from the New York State Energy and Research Development Authority (NYSERDA) and the Health Effects Institute (HEI), and utilized support services from an NIEHS Center Grant (ES 00260).
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Monitoring intraurban spatial patterns of multiple combustion air pollutants in New York City: Design and implementation
Journal of Exposure Science & Environmental Epidemiology (2013)