Ozone production rates as a function of NO_x abundances and HO_x production rates in the Nashville urban plume

Abstract

[1] Tropospheric O 3 concentrations are functions of the chain lengths of NO x (NO x NO + NO 2 ) and HO x (HO x OH + HO 2 + RO 2 ) radical catalytic cycles. For a fixed HO x source at low NO x concentrations, kinetic models indicate the rate of O 3 production increases linearly with increases in NO x concentrations (NO x limited). At higher NO x concentrations, kinetic models predict ozone production rates decrease with increasing NO x (NO x saturated). We present observations of NO, NO 2 , O 3 , OH, HO 2 , H 2 CO, actinic flux, and temperature obtained during the 1999 Southern Oxidant Study from June 15 to July 15, 1999, at Cornelia Fort Airpark, Nashville, Tennessee. The observations are used to evaluate the instantaneous ozone production rate (P O3 ) as a function of NO abundances and the primary HO x production rate (P HOx ). These observations provide quantitative evidence for the response of P O3 to NO x . For high P HOx (0.5 < P HOx < 0.7 ppt/s), O 3 production at this site increases linearly with NO to $500 ppt. P O3 levels out in the range 500-1000 ppt NO and decreases for NO above 1000 ppt. An analysis along chemical coordinates indicates that models of chemistry controlling peroxy radical abundances, and consequently P O3 , have a large error in the rate or product yield of the RO 2 + HO 2 reaction for the classes of RO 2 that predominate in Nashville. Photochemical models and our measurements can be forced into agreement if the product of the branching ratio and rate constant for organic peroxide formation, via RO 2 + HO 2 ! ROOH + O 2 , is reduced by a factor of 3-12. Alternatively, these peroxides could be rapidly photolyzed under atmospheric conditions making them at best a temporary HO x reservoir. This result implies that O 3 production in or near urban areas with similar hydrocarbon reactivity and HO x production rates may be NO x saturated more often than current models suggest.

Peroxy radical chemistry and OH radical production during the NO&lt;sub&gt;3&lt;/sub&gt;-initiated oxidation of isoprene

“…Recent field studies suggest that the radical propagating channels of RO 2 + HO 2 reactions must be significant to explain observations (Thornton et al, 2002;Lelieveld et al, 2008). Previous studies of nighttime chemistry have only considered alkene ozonolysis and HO 2 + NO, HO 2 + O 3 , and NO 3 + HO 2 reactions as sources of OH (Bey et al, 1997(Bey et al, , 2001aHarrison et al, 1998;Faloona et al, 2001;Golz et al, 2001;Geyer et al, 2003b;Ren et al, 2003;Geyer and Stutz, 2004;Vaughan et al, 2006).…”

Isoprene in poplar emissions: effects on new particle formation and OH concentrations

“…Observations of atmospheric OH concentrations indicate that under low NO x conditions isoprene may be involved in a so far unidentified recycling mechanism that converts HO 2 into OH 1022 A. Kiendler-Scharr et al: Effects on new particle formation and OH concentrations without involving ozone formation (Tan et al, 2001;Thornton et al, 2002;Ren et al, 2008;Lelieveld et al, 2008;Hofzumahaus et al, 2009;Whalley et al, 2011;Lu et al, 2011). Contrary, suppression of new particle formation by isoprene was ascribed to its suppression of OH concentrations (Kiendler-Scharr et al, 2009b).…”

Analyses of the Ozone Weekend Effect in Tokyo, Japan: Regime of Oxidant (O3 + NO2) Production

“…In order to discuss ozone production rates more specifically, the use of the VOC reactivity, that is, the reactivity of VOCs with OH radicals, is more appropriate than the VOC concentration (Sillman, 1999). In addition, the critical NMHCs/NO x ratio separating the two regimes can vary with the primary RO x production rate (P ROx ) (Thornton et al, 2002). The variation of the boundary area with P ROx , and the composition of NMHCs might cause the present result in summertime.…”