Impact of updated traffic emissions on HONO mixing ratios simulated for urban site in Houston, Texas

Abstract

Abstract. Recent measurements in Houston show that HONO traffic emissions are 1.7 % of NO x emissions, which is about twice the previously estimated value of 0.8 % based on tunnel measurements in 2001. The 0.8 % value is widely used to estimate mobile emissions of HONO for air quality modeling applications. This study applies the newly estimated HONO / NO x ratio in the WRF-SMOKE-CMAQ modeling system and estimates the impact of higher HONO traffic emissions on its mixing ratios. Since applied emission inventory resulted in overestimates of NO x mixing ratios and because HONO emissions and chemical formation depend on the magnitude of NO x , thus, before proceeding with HONO emission modifications emissions of NO x were adjusted to reflect current emission trends. The modeled mixing ratios of NO x were evaluated against measured data from a number of sites in the Houston area. Overall, the NO x mean value dropped from 11.11 ppbv in the base case to 7.59 ppbv in the NO x -adjusted case becoming much closer to the observed mean of 7.76 ppbv. The index of agreement (IOA) is improved in the reduced NO x case (0.71 vs. 0.75) and the absolute mean error (AME) is lowered from 6.76 to 4.94. The modeled mixing ratios of HONO were evaluated against the actual observed values attained at the Moody Tower in Houston. The model could not reproduce the morning HONO peaks when the low HONO / NO x ratio of 0.008 was used to estimate HONO emissions. Doubling HONO emissions from mobile sources resulted in higher mixing ratios, and the mean value increased from 0.30 to 0.41 ppbv becoming closer to the observed mean concentrations of 0.69 but still low; AME was slightly reduced from 0.46 to 0.43. IOA for simulation that used the 2001 emission values is 0.63 while for simulation with higher HONO emission it increased to 0.70. Increased HONO emissions from mobile sources resulted in a 14 % increase in OH during morning time at the location of the Moody Tower and 3 % when averaged over an urban area. The increase calculated for daytime was 7 and 1 % for the Moody Tower and the urban area, respectively. The impact on ozone was found to be marginal. This study results shed light on the underestimated HONO and OH in the morning from global/regional chemical transport models with the typical emission of 0.8 % HONO emission out of the total NO x emissions.

Combined Flux Chamber and Genomics Approach Links Nitrous Acid Emissions to Ammonia Oxidizing Bacteria and Archaea in Urban and Agricultural Soil

“…92−97 However, it remains to be seen whether biogenic HONO emissions are important in urban areas with high NO x concentrations, where photochemistry, heterogeneous reactions, and direct emissions from combustion may be the dominant HONO sources. 5,98 Lastly, it is possible that microbial activity may be a dominant source of atmospheric HONO in remote areas where ambient NO x levels are typically low. This includes arctic regions where AOA have been shown to outnumber AOB and are major players in determining the nitrification activity of this nitrogen-limited ecosystem.…”

Comprehensive modelling study on observed new particle formation at the SORPES station in Nanjing, China

“…thermal lifetimes of CIs, pressure dependency). In addition, owing to the significantly incomplete knowledge of HONO sources, in particular during daytime, it has not yet been possible to simulate realistic HONO levels using current models (Elshorbany et al, 2014;Czader et al, 2015). The lack of HONO measurement input to the model might also result in an underestimation of sulfuric acid, especially with dramatically increasing traffic emissions during the rush hours .…”

Gaseous nitrous acid (HONO) and nitrogen oxides (NOx) emission from gasoline and diesel vehicles under real-world driving test cycles

“…Recently, Rappengluck et al (2013) performed a continuous measurement at a highway junction in Houston, TX, and reported a HONO to NO x ratio of approximately 1.7%. Based on this result, a close HONO/NO x ratio of 1.6% was used to stimulate HONO emission for an urban site in Texas by Czader et al (2015). The authors reported increased HONO mixing ratios during morning peak hours and its impact of 14% OH increment in the morning at the measurement site and an overall 3% OH increment for the urban area.…”