Research publications
Permanent URI for this collection
Browse
Browsing Research publications by Author "53dd5b430c50c6f3c3082cb83b87f8c4"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Open Access A Comparative Study of Ozone Production in 5 U.S. Metropolitan Areas(AGU, 2005) Kleinman, Lawerence I.; Daum, Peter H.; Lee, Yin-Nan; Nunnermacker, Linda J.; Springston, Stephen R.; Weinstein-Llyod, Judith; Rudolph, JochenWe present observations of O3 and O3 precursors measured at mid boundary layer altitude during field campaigns in Nashville, Tennessee (1995), New York City, New York (1996), Phoenix, Arizona (1998), Philadelphia, Pennsylvania (1999), and Houston, Texas (2000). Ozone production rates P(O3) and their sensitivity to NOx and volatile organic carbons (VOCs) are calculated using observed concentrations as inputs to a steady state box model. City to city comparisons are made to illustrate common features of urban photochemistry and features that are unique to specific cities. Ozone production rates vary from nearly zero to 155 ppb h−1. Differences in P(O3) depend on precursor concentrations, namely, radical sources, NOx and VOCs. Under conditions where P(O3) is greater than 25 ppb h−1, there is a potential to produce enough same‐day O3 to transform a typical regional background into a severe O3 episode. Six such cases were observed, in Nashville, Philadelphia, and Houston, with elevated O3 concentrations in the afternoon (130–211 ppb) following a morning in which P(O3) was 25–140 ppb h−1. High P(O3) occurs when NOx concentrations are 5–25 ppb and OH‐VOC reactivity is above 5 s−1. These conditions are infrequent, and aside from a common dependence on calm winds, reasons vary from city to city. In Nashville, high P(O3) was observed during a stagnation event over downtown and under the circumstance that an air mass with a high concentration of isoprene encountered a NOx source. In Houston, NOx and light olefins are coemitted from petrochemical facilities leading to the highest P(O3)s of the five cities studied. High values of P(O3) did not occur in Phoenix because of low radical production, caused mainly by a dry atmosphere, and a low VOC to NOx ratio. The sensitivity of P(O3) to its precursors varied from NOx limited in rural samples to VOC limited near emission sources. In Philadelphia, and especially Phoenix, the highest O3 production rates occurred under VOC‐limited conditions. In Nashville, New York City, and Houston the high‐P(O3) samples were near the ridge line where P(O3) responds somewhat to VOC reductions but is insensitive to NOx changes.Item Open Access Ozone production efficiency in an urban area(AGU, 2002) Kleinman, Lawerence I.; Daum, Peter H.; Lee, Yin-Nan; Nunnermacker, Linda J.; Springston, Stephen R.; Weinstein-Llyod, Judith; Rudolph, JochenOzone production efficiency can be defined as the number of molecules of oxidant (O3 + NO2) produced photochemically when a molecule of NOx (NO + NO2) is oxidized. It conveys information about the conditions under which O3 is formed and is an important parameter to consider when evaluating impacts from NOx emission sources. We present calculational and observational results on ozone production efficiency based on measurements made from aircraft flights in the Phoenix metropolitan area in May and June of 1998. Constrained steady state box model calculations are used to relate a ratio of O3 production rate to NOx consumption rate (i.e., P(O3)/P(NOz)) to a VOC to NO2 ratio of OH reactivity. Lagrangian calculations show how this ratio generally increases with time due to oxidation chemistry and plume dilution. City to city differences in ozone production efficiency can be attributed to corresponding differences in VOC to NO2 reactivity ratio which in turn reflect emission patterns. Ozone production efficiencies derived from aircraft measurements in 20 plumes show a dependence on NOx concentration similar to that calculated for P(O3)/P(NOz). Calculations are based on data from a single location but are believed to be applicable to a wide range of plumes from different areas.Item Open Access Photochemical age determinations in the Phoenix metropolitan area(AGU, 2003) Kleinman, Lawerence I.; Daum, Peter H.; Lee, Yin-Nan; Nunnermacker, Linda J.; Springston, Stephen R.; Weinstein-Llyod, Judith; Hyde, Peter; Doskey, Paul; Rudolph, J.; Fast, Jerome; Berkowitz, CarlAn extensive VOC data set was gathered as part of a photochemical oxidant field campaign conducted in the Phoenix air basin in the late spring of 1998. Sampling was done at the surface and by aircraft at midboundary layer height; in regions with emission sources and downwind in the urban plume. VOC concentration ratios were used to calculate photochemical age, defined as the time integrated exposure of an air mass to OH radical. Based on the VOC ratios of 15 compounds (with OH reactivity varying between acetylene and p, m-xylene), we present estimates for photochemical age and dilution factors for several regions within the air basin. Geographic trends are in agreement with the expectation that pollutants are transported in a generally eastward direction so that older and more dilute mixtures occur to the east of the city. Photochemical ages determined from aircraft samples agree with those determined at a downwind surface site. The bias in photochemical age that occurs because fresh pollutants are added to an aged mixture has been quantified by using a particle trajectory model. A combination of trajectory results (actual age of the pollutants in an air mass) and photochemical age yields an estimate of the average OH concentration experienced by the air parcel. OH obtained in this way is somewhat lower, but has the same trends as OH concentrations calculated using a photochemical box model that is constrained with observed concentrations coincident with the VOC samples.Item Open Access Sensitivity of ozone production rate to ozone precursors(AGU, 2001) Kleinman, Lawerence I.; Daum, Peter H.; Lee, Yin-Nan; Nunnermacker, Linda J.; Springston, Stephen R.; Weinstein-Lloyd, Judith; Rudolph, J.The photochemical equations describing O3 formation in the lower troposphere contain 2 major sink terms for free radicals; combination reactions and reactions with NOx. Knowing the fraction of radicals removed by reactions with NOx, termed LN/Q, allows one to predict the sensitivity of O3 production to NO and VOCs. We derive an analytic formula that gives LN/Q in terms of readily measured O3 precursors and test this formula using constrained steady state calculations based on field observations gathered in Phoenix, Arizona. The formula quantifies well‐known results regarding the effects of dilution, oxidation, and the production of oxidants on the transition from VOC to NOx sensitive behavior as an air parcel is advected away from an urban source.