Grantee Research Project Results
Final Report: The Impact of Aerosols, Clouds, and Ozone on Surface UV and Photochemistry in Houston, TX
EPA Grant Number: R833225Title: The Impact of Aerosols, Clouds, and Ozone on Surface UV and Photochemistry in Houston, TX
Investigators: Lefer, Barry , Slusser, James , Byun, Daewon , Rappenglueck, Bernhard , Chellam, Shankar
Institution: University of Houston , Colorado State University
EPA Project Officer: Chung, Serena
Project Period: March 15, 2007 through March 14, 2009 (Extended to March 14, 2011)
Project Amount: $292,310
RFA: Implications of Tropospheric Air Pollution for Surface UV Exposures (2005) RFA Text | Recipients Lists
Research Category: Climate Change , Air Quality and Air Toxics , Air
Objective:
Air quality in Eastern Texas, particularly the Houston and Dallas-Fort Worth metropolitan areas, suffers from high ozone levels. The problem is aggravated by the emissions of NOx (NO and NO2) from metropolitan traffic and power plants; distributions of Volatile Organic Compounds (VOCs) from chemical processing plants; and biogenic emissions of isoprene, a VOC species, from plants. In the presence of sunlight, VOCs and NOx react in complex ways to form ozone. To study the severity of such air pollution problems and to provide tools for the development of an emissions control strategy, comprehensive state-of-science atmospheric measurement efforts have provided a wealth of data that needs to be modeled and analyzed. One of the key challenges of such an effort is to establish a consistent research information infrastructure that combines various modeling systems. In many cases, new measurement and modeling tools need to be developed at achieve this goal. This project addresses the advancement of an integrated measurement and modeling efforts to understand the TexAQS-II episodes and to better characterize the regional and local air quality problems.
Summary/Accomplishments (Outputs/Outcomes):
One of the major findings of this research is that the accuracy of meteorological modeling in the Houston urban environment is significantly improved when the land Surface processes were accurately described by detailed land use (LU) and land cover (LC) data (Cheng and Byun, 2008). Not surprisingly, the improvements in meteorological modeling directly impacted CMAQ Air quality simulations near the Houston Ship Channel (HSC) where the updating the LULC from grass land to impervious "urban" land use enhanced mixing of the precursor species and resulted in a significantly better ozone prediction (Cheng et al., 2008). Previous studies of Houston air quality have identified that emissions from Houston’s industrial sources contribute significantly to elevated ozone concentrations and make Houston’s air composition quite unique in comparison to typical urban composition. To address this issue, source-oriented reactivities of individual organic compounds with regard to ozone formation were determine and then used to develop an extended version of SAPRC-99 mechanism for the CMAQ model. According to the reactivities weighted by VOC mixing ratios, ethene, propene and formaldehyde show the highest impact on ozone formation (Czader et al., 2008). The UH team also learned that the prediction of PM2.5 by CMAQ can be significantly improved by the initialization of the aerosol fields with the satellite-derived Aerosol Optical Depth (AOD), though further refinements of the vertical distribution of aerosols are critically needed (Lee et al., 2011).
By analyzing the synoptic flow patterns over eastern Texas and adjacent states during the 2005/06 Second Texas Air Quality Studies (TexAQS-II) and classifying then into six groups, the UH team was able to identify which synoptic weather patterns are conducive to creating high- and low0ozone events. Southerly synoptic flows and higher average wind speeds were related to low ozone levels while easterly and northerly flow had a higher probably to exceed the 8-h ozone standard. The dry and sunny postfrontal days with weak northerly or easterly weather patterns were often associated with ozone exceedances in the Houston-Galveston-Brazoria area during September 2006. Flow from the east, which brought polluted air from the Houston Ship Channel resulting in high ozone in the southwestern part of the metropolitan area (see Ngan and Byun (2011)). Because most 3-D chemical transport models over-estimate ozone mixing ratios in flow from the Gulf of Mexico, an effort to address this issue by modifying the dry deposition module in CMAQ such at hat iodide reacts with ozone in seawater. In addition, an attempt was made to incorporate iodide concentrations from the satellite-derived estimates of near-surface chlorophyll A concentrations into the CMAQ gridded fields. The resulting increase in ozone dry deposition amounts showed that this iodide-ozone interaction affects ozone mixing ratios in the inland coastal area (Oh et al., 2008).
In this project we also assessed the impact of the downscale linkage of global chemistry model output on the simulated regional scale O3 concentration and its vertical and horizontal structure over the continental US. RAQMS simulation results were downscaled with a RAQMS-CMAQ linkage tool to provide dynamic lateral boundary conditions for regional air quality simulations to the EPA CMAQ model. The CMAQ simulations with the improved RAQMS-base lateral boundary condition showed improved diurnal variations and daily maxima of surface O3 concentrations and produced better agreement with the vertical structure of O3 measured in the middle and upper troposphere. Tracer mode simulations showed that, at the upper troposphere, more than 85% of the O3 concentration difference associated with the lateral BCs was caused by the transport and diffusion processes (Song et al., 2008).
The nocturnal boundary layer in Houston was studied using a tethersonde system showed that a weakly stable surface inversion averaging in depth between 145 and 200 m AGL formed at night, within 2-3 h after sunset (Day et al.,2010). A long-term study using a lidar ceilometer provided continuous diurnal PBL height also show nocturnal PBL heights range from 100 to 300 m throughout the year while the convective PBL ranges from 1100 m in the winter to 2000 m in the summer (Haman et al., 2012). On 11 days during TexAQS-II ozonesondes were launched both at dawn and in the afternoon, analysis of this data shows that morning residual layer (RL) ozone concentrations explained 60-70% of the variability in the afternoon mixed layer (ML). Furthermore, maximum RL [O3] is nearly identical to the mean ML [O3] from the previous afternoon (Morris et al., 2010).
During TexAQS-II, VOCs measured at the urban Moody Tower (MT) revealed that natural gas/crude oil contributed most of the VOC mass, followed by liquefied petroleum gas, vehicular exhaust, fuel evaporation, and aromatics. Petrochemical sources from ethylene and propylene also play an important role. A minor fraction can be attributed to biogenic sources (Leuchner and Rappenglueck, 2010). Similarly, HCHO levels at this site were dependent on the wind direction: southerly maritime winds (background levels) while airmasses from the HSC resulted in high HCHO. The HCHO levels at the MT site accounted for primary vehicular emissions (38.5 ± 12.3%), photochemically produced (24.1 ± 17.7%), and industrial emissions (8.9 ± 11.2%). Aside from traffic-related primary HCHO emissions, HCHO of industrial origin serves as an appreciable source for OH in the morning (Rappenglueck et al., 2010).
A comparison of five widely known chemical mechanisms (RACM, CB05, LaRC, SAPRC-99, SAPRC-07, and MCMv3.1) using TexAQS-II field data showed that measured OH and HO2 are greater than modeled for all mechanisms. Modeled and measured ratios of HO2/OH suggests that chemical mechanisms do better in high rather than low NOx environments (Chen et al., 2010). An examination of the effects of clouds and aerosols on photolysis rates determine that the combined effect of clouds and aerosols during the TexAQS II was to reduce j(NO2) photolysis frequencies by 17%, which translated in to a reduction in net ozone production of 8 ppbv per hr (Flynn et al.,2010). Several high-ozone episodes encountered at Moody Tower during the 2006 TexAQS-II campaign were preceded one to two days earlier by a cold front passage. In addition, it was determined that the 2006 TexAQS-II time period is more representative of typical Houston climatic conditions than the weather during TexAQS-2000 (Lefer et al., 2010). The lowest concentrations of all primary (CO, NO, NO2, SO2) and secondary species (HNO3, PAN, O3, NOz) were observed in marine air (southerly flow). SO2 concentrations were low, but increased dramatically in sporadic midday plumes advected from the HSC. CO/NOX emission ratios of 5.81 ± 0.94 were observed in the morning rush hour, while HNO3 and PANs comprised the dominant NOZ species. Overall, our findings confirm the impact of the HSC as a dominant source region within the HMA (Luke et al., 2010) .
Similarities and differences in summertime atmospheric photochemical oxidation appear in the comparison of four field studies: TexAQS2000 (Houston, 2000), NYC2001 (New York City, 2001), MCMA2003 (Mexico City, 2003), and TRAMP2006 (Houston, 2006). In terms of photochemical activity, Houston is much more like Mexico City than New York City. In all four studies, the photolysis of HONO and HCHO are significant HOx sources. Photochemical indicators show particularly high photochemical activity in Houston and provide support for regulatory actions that aim to reduce reactive VOCs (Mao et al., 2010). During this study Ship Channel petrochemical flares were observed to produce plumes of apparent primary HCHO. Simulations with the CAMx model show that additional emissions of HCHO from industrial flares or mobile sources can increase peak ozone in Houston by up to 30 ppb. Results from this study also show that HONO may be formed heterogeneously on urban canopy or particulate matter surfaces and may be enhanced by organic aerosol of industrial or motor vehicular origin, such as through conversion of nitric acid (HNO3). Additional HONO sources may increase daytime ozone by more than 10 ppbv. (Olaguer et al., 2010).
The sensitivity of biogenic emission estimates and air quality model predictions to the characterization of LULC in southeastern Texas was examined using GloBEIS and CAMx. A LULC database was developed for the region based on satellite imagery and field data for land cover classification, species identification and quantification of biomass densities. Biogenic emissions estimated from the new LULC data set showed good general agreement in their spatial distribution, but were approximately 40% lower than emissions from the LULC data set used by the State of Texas. Predicted ozone mixing ratios using the biogenic emissions produced from the new LULC data set were as much as 26 ppb lower in some areas on some days, depending on meteorological conditions. (Feldman et al., 2010).
Assessment of fine particulate matter data from New York, NY; Baltimore, MD; Pittsburgh, PA; Atlanta, GA; Houston, TX; St. Louis, MO; and Fresno, CA, indicates that in virtually all of the regions, transport of aerosol over distances of 100-1000 km has a significant impact on urban particulate matter concentrations and a dominant role in determining rural particulate matter concentrations and is generally consistent with previous conceptual models of fine particulate matter formation and accumulation in these regions. The nature of the transported aerosol is largely sulfate in Eastern and Midwestern cities and nitrate in the Central Valley of California. Regional nucleation events have been reported in the East, Midwest, and in California. In some cases, these nucleation events have been correlated with availability of sulfur dioxide and, therefore, may be sulfate formation events (Allen and Turner, 2008). Secondary formation, which is often regional in nature, drives fine particulate matter mass and the relevant chemical components toward high intraurban spatial homogeneity. Particulate matter components that are dominated by primary emissions within the urban area tend to exhibit greater spatial heterogeneity (Turner and Allen, 2008).
The Chemical Mass Balance (CMB) receptor model is commonly used to evaluate the relationship between emissions of air pollutants and their concentration in the ambient air, however it is not clear that it can accurately achieve this goal when evaluating sources of reactive air pollutants such as non-methane hydrocarbons (NMHC). In many of the cases that result in a solution, CMB fails to identify or attribute the mass of a relevant source to within 30% of the true contribution, or identifies irrelevant sources and attributes more than 5% of the total mass to them. When composite aged profiles are made available to the model, inaccuracy is eliminated but many cases still do not result in a solution (Wittig and Allen, 2008).
A tall tower flux measurement setup was established in metropolitan Houston, Texas, to measure trace gas fluxes from emission sources in the urban surface layer. A relaxed eddy accumulation (REA) system combined with a dual-channel GC-FID was used for VOC flux measurements, focusing on benzene, toluene, ethylbenzene and xylenes (BTEX). The measured values exhibited diurnal cycles with dominant morning and midday peaks during weekdays related to rush hour traffic and additional weekday daytime toluene and xylenes emissions. Local evaporative emissions, likely from solvent usage, significantly contributed to the measured fluxes. The measured emissions were upscaled to the county level and compared with EPA's National Emission Inventory (NEI) (Park et al., 2010). Measurements of the mixing ratios and fluxes of isoprene and its oxidation products, methacrolein (MACR) and methyl vinyl ketone (MVK) show that isoprene was affected dominantly by biogenic emission sources during daytime, but also that tail-pipe emission sources (alongside 2-pentenes) are contributing during the rush hours and at night. These results suggest that emission inventories used for ozone modeling may need to consider tailpipe isoprene (and MACR) emissions to properly account for urban concentrations, particularly higher morning abundances (Park et al., 2011).
Air quality measurements obtained at a park site southeast of College Station, TX, during the 2006 Texas Air Quality Study II (TexAQS) show that background ozone during exceedance days was as high as 80 ppb, whereas southerly air flows generally provided for an ozone background lower than 40 ppb. In light of these and other TexAQS findings, it appears that ozone air quality is affected throughout east Texas by both long-range and regional ozone transport, and that improvements therefore will require at least a regionally oriented instead of the current locally oriented ozone precursor reduction policies (Schade et al., 2011).
Speciated samples of PM2.5 were collected at the six sites in Southeastern Texas by US EPA (Environmental Protection Agency) from July 2003 to August 2005. These data sets were analyzed by positive matrix factorization (PMF) identified ten common source-related factors: sulphate-rich secondary aerosol I, sulphate-rich secondary aerosol II, cement/carbon-rich, wood smoke, motor vehicle/road dust, nitrate-rich secondary aerosol, metal processing, soil, sea salt, and chloride-depleted marine aerosol. The two sulphate-rich secondary aerosols account for about 40-0% of the PM2.5 mass concentration (Chiou et al., 2008, 2009ab).
Conclusions:
The process of attempting to learn more about air quality in eastern Texas in an integrative fashion, new measurement, modeling, and analysis tools were developed. In particular, we learned that improvements in meteorological modeling urban environments can be achieved when the land surface processes are more accurately described, which also results in better ozone forecasting. In addition, the prediction of PM2.5 by CMAQ can be improved by the initialization of aerosol fields with satellite-derived AODs. Similarly, CMAQ simulations with lateral boundary conditions from RAQMS improved diurnal O3 variations, daily maxima of surface O3, and the vertical structure of O3 in the middle and upper troposphere.
From analysis of observations it was determined that the TexAQS-II study, the O3 exceedance days characterized as dry and sunny postfrontal days with weak northerly or easterly weather patterns. In addition, PBL heights range from 100 - 300 m while the convective PBL is typically 2000 m in the summer. Ozonesonde data shows that morning residual layer (RL) ozone concentrations explained 60-70% of the variability in the afternoon mixed layer (ML) and the maximum RL [O3] is nearly identical to the mean ML [O3] from the previous afternoon. Box modeling studies show that chemical mechanisms do better in high rather than low NOx environments and that clouds and aerosols reduced net ozone production by 8 ppbv per hr during this campaign. Our assessment of fine particulate matter data indicates that in the transport of aerosol over distances of 100-1000 km has a significant impact on urban particulate matter concentrations and a dominant role in determining rural particulate matter concentrations.
A major finding was that the photolysis of HONO and HCHO are significant OH sources in Houston. While a significant fraction of the HCHO is from “primary” sources (both automobiles and flares), these studies revealed that HONO is likely formed heterogeneously on both the urban canopy and on aerosol surfaces. Similarly, our results suggest that emission inventories need to consider tailpipe isoprene (and MACR). While our findings confirm the impact of the HSC as a dominant source region within the HMA, air quality is affected throughout east Texas by both long-range and regional ozone transport, and that improvements therefore will require a regionally oriented instead of the current locally oriented ozone precursor reduction policies.
Journal Articles on this Report : 29 Displayed | Download in RIS Format
| Other project views: | All 38 publications | 33 publications in selected types | All 33 journal articles |
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Chen S, Ren X, Mao J, Chen Z, Brune WH, Lefer B, Rappengluck B, Flynn J, Olson J, Crawford JH. A comparison of chemical mechanisms based on TRAMP-2006 field data. Atmospheric Environment 2010;44(33):4116-4125. |
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Flynn J, Lefer B, Rappengluck B, Leuchner M, Perna R, Dibb J, Ziemba L, Anderson C, Stutz J, Brune W, Ren X, Mao J, Luke W, Olson J, Chen G, Crawford J. Impact of clouds and aerosols on ozone production in Southeast Texas. Atmospheric Environment 2010;44(33):4126-4133. |
R833225 (2007) R833225 (2008) R833225 (Final) |
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Lefer B, Rappenglück B, Flynn J, Haman C. Photochemical and meteorlogical relationships during the Texas-II Radical and Aerosol Measurement Project (TRAMP). Atmospheric Environment 2010;44(33):4005-4013. |
R833225 (2007) R833225 (Final) |
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Luke WT, Kelley P, Lefer BL, Flynn J, Rappengluck B, Leuchner M, Dibb JE, Ziemba LD, Anderson CH, Buhr M. Measurements of primary trace gases and NOY composition in Houston, Texas. Atmospheric Environment 2010;44(33):4068-4080. |
R833225 (2008) R833225 (Final) |
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Mao J, Ren X, Chen S, Brune WH, Chen Z, Martinez M, Harder H, Lefer B, Rappengluck B, Flynn J, Leuchner M. Atmospheric oxidation capacity in the summer of Houston 2006: comparison with summer measurements in other metropolitan studies. Atmospheric Environment 2010;44(33):4107-4115. |
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Morris GA, Ford B, Rappengluck B, Thompson AM, Mefferd A, Ngan F, Lefer B. An evaluation of the interaction of morning residual layer and afternoon mixed layer ozone in Houston using ozonesonde data. Atmospheric Environment 2010;44(33):4024-4034. |
R833225 (2008) R833225 (Final) |
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Olaguer EP, Rappengluck B, Lefer B, Stutz J, Dibb J, Griffin R, Brune WH, Shauck M, Buhr M, Jeffries H, Vizuete W, Pinto JP. Deciphering the role of radical precursors during the Second Texas Air Quality Study. Journal of the Air & Waste Management Association 2009;59(11):1258-1277. |
R833225 (2008) R833225 (Final) |
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Czader BH, Byun DW, Kim ST, Carter WP. A study of VOC reactivity in the Houston-Galveston air mixture utilizing an extended version of SAPRC-99 chemical mechanism. Atmospheric Environment 2008;42(23):5733-5742. |
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Cheng FY, Byun DW. Application of high resolution land use and land cover data for atmospheric modeling in the Houston–Galveston metropolitan area, Part I:Meteorological simulation results. Atmospheric Environment 2008;42(33):7795-7811. |
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Chiou P, Tang W, Lin CJ, Chu HW, Tadmor R, Ho TC. Atmospheric aerosols over two sites in a southeastern region of Texas. The Canadian Journal of Chemical Engineering 2008;86(3):421-435. |
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Song CK, Byun DW, Pierce RB, Alsaadi JA, Schaack TK, Vukovich F. Downscale linkage of global model output for regional chemical transport modeling: method and general performance. Journal of Geophysical Research: Atmospheres 2008;113(D8). |
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Clements CB, Zhong S, Bian X, Heilman WE, Byun DW. First observations of turbulence generated by grass fires. Journal of Geophysical Research:Atmospheres 2008;113(D22). |
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Wittig AE, Allen DT. Improvement of the Chemical Mass Balance model for apportioning—sources of non-methane hydrocarbons using composite aged source profiles. Atmospheric Environment 2008;42(6):1319-1337. |
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Oh IB, Byun DW, Kim HC, Kim S, Cameron B. Modeling the effect of iodide distribution on ozone deposition to seawater surface. Atmospheric Environment 2008;42(19):4453-4466. |
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Turner JR, Allen DT. Transport of atmospheric fine particulate matter:part 2—findings from recent field programs on the intraurban variability in fine particulate matter. Journal of the Air & Waste Management Association 2008;58(2):196-215. |
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Chiou P, Tang W, Lin CJ, Chu HW, Ho TC. Atmospheric aerosol over a southeastern region of Texas:chemical composition and possible sources. Environmental Modeling & Assessment 2009;14:333-350. |
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Chiou P, Tang W, Lin CJ, Chu HW, Ho TC. Comparison of atmospheric aerosols between two sites over golden triangle of Texas. Environmental Research 2009;3:253-270. |
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Feldman MS, Howard T, McDonald-Buller E, Mullins G, Allen DT, Hansel A, Wisthaler A. Applications of satellite remote sensing data for estimating biogenic emissions in southeastern Texas. Atmospheric Environment 2010;44(7):917-929. |
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Park C, Schade GW, Boedeker I. Flux measurements of volatile organic compounds by the relaxed eddy accumulation method combined with a GC-FID system in urban Houston, Texas. Atmospheric Environment 2010;44(21-22):2605-2614. |
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Rappenglück B, Dasgupta PK, Leuchner M, Li Q, Luke W. Formaldehyde and its relation to CO, PAN, and SO 2 in the Houston-Galveston airshed. Atmospheric Chemistry and Physics 2010;10(5):2413-2424. |
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Day BM, Rappenglück B, Clements CB, Tucker SC, Brewer WA. Nocturnal boundary layer characteristics and land breeze development in Houston, Texas during TexAQS II. Atmospheric Environment 2010;44(33):4014-4023. |
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Stutz J, Oh HJ, Whitlow SI, Anderson C, Dibb JE, Flynn JH, Rappenglück B, Lefer B. Simultaneous DOAS and mist-chamber IC measurements of HONO in Houston, TX. Atmospheric Environment 2010;44(33):4090-4098. |
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Leuchner M, Rappenglück B. VOC source–receptor relationships in Houston during TexAQS-II. Atmospheric Environment 2010;44(33):4056-4067. |
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Park C, Schade GW, Boedeker I. Characteristics of the flux of isoprene and its oxidation products in an urban area. Journal of Geophysical Research:Atmospheres 2011;116(D21). |
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Ngan F, Byun D. Classification of weather patterns and associated trajectories of high-ozone episodes in the Houston–Galveston–Brazoria area during the 2005/06 TexAQS-II. Journal of Applied Meteorology and Climatology 2011;50(3):485-499. |
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Lee D, Byun DW, Kim H, Ngan F, Kim S, Lee C, Cho C. Improved CMAQ predictions of particulate matter utilizing the satellite-derived aerosol optical depth. Atmospheric Environment 2011;45(22):3730-3741. |
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Schade GW, Khan S, Park C, Boedeker I. Rural southeast texas air quality measurements during the 2006 texas air quality study. Journal of the Air & Waste Management Association 2011;61(10):1070-1081. |
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Wong KW, Tsai C, Lefer B, Haman C, Grossberg N, Brune WH, Ren X, Luke W, Stutz J. Daytime HONO vertical gradients during SHARP 2009 in Houston, TX. Atmospheric Chemistry and Physics 2012;12(2):635-652.. |
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Haman CL, Lefer B, Morris GA. Seasonal variability in the diurnal evolution of the boundary layer in a near-coastal urban environment. Journal of Atmospheric and Oceanic Technology 2012;29(5):697-710. |
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Supplemental Keywords:
atmospheric monitoring, atmospheric modeling, planetary boundary layer, Air quality forecasting, VOC, PMF, data assimilation, PM, aerosol composition, secondary organics, aerosol aging, urban flux projectProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.