Ozone production and its sensitivity to NO<sub><i>x</i></sub> and VOCs: results from the DISCOVER-AQ field experiment, Houston 2013

Abstract

Abstract. An observation-constrained box model based on the Carbon Bond mechanism, version 5 (CB05), was used to study photochemical processes along the NASA P-3B flight track and spirals over eight surface sites during the September 2013 Houston, Texas deployment of the NASA Deriving Information on Surface Conditions from COlumn and VERtically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) campaign. Data from this campaign provided an opportunity to examine and improve our understanding of atmospheric photochemical oxidation processes related to the formation of secondary air pollutants such as ozone (O3). O3 production and its sensitivity to NOx and volatile organic compounds (VOCs) were calculated at different locations and times of day. Ozone production efficiency (OPE), defined as the ratio of the ozone production rate to the NOx oxidation rate, was calculated using the observations and the simulation results of the box and Community Multiscale Air Quality (CMAQ) models. Correlations of these results with other parameters, such as radical sources and NOx mixing ratio, were also evaluated. It was generally found that O3 production tends to be more VOC-sensitive in the morning along with high ozone production rates, suggesting that control of VOCs may be an effective way to control O3 in Houston. In the afternoon, O3 production was found to be mainly NOx-sensitive with some exceptions. O3 production near major emissions sources such as Deer Park was mostly VOC-sensitive for the entire day, other urban areas near Moody Tower and Channelview were VOC-sensitive or in the transition regime, and areas farther from downtown Houston such as Smith Point and Conroe were mostly NOx-sensitive for the entire day. It was also found that the control of NOx emissions has reduced O3 concentrations over Houston but has led to larger OPE values. The results from this work strengthen our understanding of O3 production; they indicate that controlling NOx emissions will provide air quality benefits over the greater Houston metropolitan area in the long run, but in selected areas controlling VOC emissions will also be beneficial.

Observed and Model-Derived Ozone Production Efficiency over Urban and Rural New York State

“…These model-derived and observed OPEs are consistent with OPEs found in other urban locations (e.g., [4,5,10]). In contrast, CMAQ-predicted and observed OPEs at QC when only NYS DEC data was used to determine observed OPEs were in poor agreement, with CMAQ-predicted OPEs of approximately 4-7 and observed OPEs of approximately 11-25 during the study period.…”

“…This table indicates that the model-predicted and observed OPEs at QC were in good agreement, differing by no more than approximately 2 during the study period. In addition, the August and September observed OPEs of 7.70 and 6.16 are comparable to OPEs observed in other urban areas (e.g., [4,5,10] Table 3. These results show that (1) the model-predicted and observed background [O 3 ] concentrations at QC differed by approximately 1-2 ppb in August and 8-10 ppb in September, and (2) model-predicted and observed O x and NO z were well-correlated, with model-derived and observed R 2 values greater than 0.50 for both months.…”

“…Although defining the OPE as ∆O x /∆NO z has the advantage of only focusing on photochemical O 3 production by VOC oxidation, instead of O 3 variations caused by NO titration [5], there are some potential limitations associated with this definition. Namely, if there is considerable dry depositional loss of HNO 3 , the OPE is biased high due to the reduction in the [NO z ] concentration [4,9,27,28]. In addition, not only does the specification of the OPE as ∆O x /∆NO z exclude the effect of dry deposition, it also does not account for mixing and fresh emissions [10].…”

The Uncertain Role of Biogenic VOC for Boundary-Layer Ozone Concentration: Example Investigation of Emissions from Two Forest Types with a Box Model

“…Because of several stresses herbivorous plants have adopted several defense mechanisms, which enable them to tolerate different stresses at different intensities, for example different temperatures or ozone levels [8]. One of these mechanisms seems to work by using the and climate models but also for air quality and pollution forecasts [28][29][30]. A reliable match between simulation and observation is therefore key for predicting health issues and ecosystem damage.…”

“…On the contrary, wind speed acts as a reductive, as less dilution of precursor gases occurs and so more time is available to locally produce ozone. and pollution forecasts [28][29][30]. A reliable match between simulation and observation is therefore key for predicting health issues and ecosystem damage.…”