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Response to Comment on “Tracking Petroleum Refinery Emission Events Using Lanthanum and Lanthanides as Elemental Markers for PM2.5” Hendler’s comments do not contest the central theme of our paper (1) that detailed chemical composition of lanthanides can be used to track FCC emissions but rather questions clearly documented assumptions in our original paper that were necessary because information from local industrial sources was neither readily available nor forthcoming, even upon our repeated requests.
REE Enrichment during Episode Cannot Be Attributed to Saharan Dust Table 1 in the Supporting Information summarizes La to light rare earth element (REE) ratios from various natural and anthropogenic sources. All ratios closely matched for FCC catalysts and ambient PM measured in Channelview, which is consistent with earlier measurements in Philadelphia. In contrast, the same ratios are significantly different (by a factor between 4.6 and 7.8 using the mean values) between ambient PM at Channelview and Saharan dust. Elevated La/V ratios also demonstrate that primary emissions of catalyst dominated ambient PM levels. We performed source apportionment with EPA’s CMB8 model (in addition to eq 1 of the original paper) to separately attribute elevated PM mass to refinery emissions and Saharan dust. Ambient data from Channelview during the episode and the best available source profiles for Saharan dust (2) and FCC catalyst material (3) were used. CMB calculations for the ambient data collected in Channelview using markers (La, Ce, Pr, Nd, Sm) with both Saharan dust and FCC catalyst sources lead to colinearity and lack of convergence. However, running CMB with only a single source separately for FCC catalyst and Saharan dust yielded good performance for the single FCC catalyst source (r2 ) 0.97, Chi2 ) 15) while the model failed to converge for the single source model run with only Saharan dust. This justifies our original use of a simplified source attribution model. Hence, the dominant cause of REE enrichment in Channelview is confirmed to be FCC emissions rather than the transport of Saharan dust into the region.
Spatial Uniformity of PM during Episode We believe that our data shows that the relative contributions of FCC emissions during the episode and transported regional haze were different at each of the four sites during the same time frame resulting in relatively uniform PM levels. Our original manuscript acknowledged the apparent lack of increase in ambient PM2.5 mass at Channelview compared to the other sites despite the elevated FCC contribution, and noted that the poor temporal resolution for the TEOM filter samples (where collected PM is aggregated over numerous days) may be partly responsible. As suggested by Hendler, reintrainment of material may extend the period of influence beyond the reported emission period leading to lower peak contribution over an extended period. To overcome this, we are currently undertaking an 18 month sampling campaign using daily filter collection to better characterize the contribution of transient emissions caused by nonroutine operation of local industrial sources. Further, we stressed in our paper that detailed quantification of unique tracers that can be used to isolate contributions of a single source is exactly the type of measurement needed to understand the roles of multiple sources during regional haze episodes. 2990
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CMB calculations reported in our paper (1) attributed 12% of PM mass even during the extended duration (240 h) of TEOM sampling to the FCC source. As mentioned therein, a higher FCC contribution to PM2.5 mass would be expected during the short duration emission event. Importantly, concentrations of several marker elements representing nonFCC sources decreased at Channelview during the event as compared to concentrations measured at East Houston, Clinton, and Kingwood, indicating that other sources had less of an impact at Channelview during the episode (Supporting Information Table 2). In summary, we believe the question regarding spatially uniform PM levels is a valid concern. However, our measurements are accurate and with several corroborations stated above, we simply cannot ignore high FCC contribution at Channelview. This formed the initial basis for our original conclusion that at Channelview, regional haze had lesser impact during the same time frame.
Lanthanum Content of FCC Catalysts and Related Source Contribution Calculations It is purported by Mr. Hendler (without any details of analytical protocols) that the La content in the actual catalyst released during the emission event was 2.5 times higher than the value used in our work (3). Our ICP-MS technique has been cross validated using ICP-OES and neutron activation and subjected to peer-review (4) thereby constituting a scientifically defendable data set of the elemental composition of FCC catalysts. If Hendler’s undocumented information is correct, the episodic contribution would reduce to 7.5 µg/m3 from 15.9 µg/m3. In the future, we hope that industry will respond to our requests for catalyst samples specific to the refining processes employed in individual petrochemical plants so that we can accurately and cooperatively establish the impact from different facilities to local PM levels. A closer collaboration between industry and academia would resolve such differences in numerical estimates of the industrial impacts on the environment. We look forward to a fruitful partnership with petroleum refiners in order to meet serious air quality problems in the greater Houston area, fully acknowledging their positive economic impacts.
Supporting Information Available Summary of La to light REE ratios from Saharan dust, ambient PM and FCC catalyts. This material is available free of charge via the Internet at http://pubs.acs.org.
Literature Cited (1) Kulkarni, P.; Chellam, S.; Fraser, M. P. Tracking petroleum refinery emission events using lanthanum and lanthanides as elemental markers for PM2.5. Environ. Sci. Technol. 2007, 41 (19), 6748–6754. (2) Moreno, T.; Querol, X.; Castillo, A.; Alastuey, A.; Cuevas, E.; Herrmann, L.; Mounkaila, M.; Elvira, J.; Gibbons, W. Geochemical variations in aeolian mineral particles from the SaharaSahel dust corridor. Chemosphere 2006, 65, 261–270. (3) Kulkarni, P.; Chellam, S.; Fraser, M. P. Lanthanum and lanthanides in atmospheric fine particles and their apportionment to refinery and petrochemical operations in Houston, TX. Atmos. Environ. 2006, 40, 508–520. (4) Kulkarni, P.; Chellam, S.; Mittlefehldt, D. W. Microwave assisted extraction of rare earth elements from petroleum refining catalysts and ambient fine aerosols prior to inductively coupled plasma -mass spectrometry. Anal. Chim. Acta 2007, 581 (2), 247–259. 10.1021/es900273s CCC: $40.75
2009 American Chemical Society
Published on Web 03/17/2009
Pranav Kulkarni Trinity Consultants, 1001 West Loop South Suite 640, Houston Texas 77027
Shankararaman Chellam Department of Civil and Environmental Engineering, University of Houston, Houston, Texas 77402-4003
Matthew P. Fraser Associate Professor, School of Sustainability, Associate Director for Research Development, Global Institute of Sustainability, Arizona State University ES900273S
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