Long-Term Measurements of NO₃Radical at a Semiarid Urban Site: 2. Seasonal Trends and Loss Mechanisms

Abstract

This study is the first to present long-term measurements of the nitrate radical in an urban location. Extensive nitrate radical measurements were conducted together with ancillary parameters during a continuous two year campaign (2005-2007) in the semiarid location of Jerusalem. The average nighttime NO3 concentration was 27.3+/-43.5 ppt, the highest ever reported, with a seasonal average peak during summer (33.3+/-55.8 pptv) with maximum levels exceeding 800 pptv. Significant diurnal changes in NO3 concentrations were observed, caused by an unusual nighttime increase in ozone concentrations. The NO3 loss processes exhibited strong seasonal variability. Homogeneous gas-phase losses were the main removal processes during summer and spring. The heterogeneous losses of N2O5, averaged over the entire campaign, contributed to less than half of the direct losses even though they dominated the winter seasons and part of the autumn months. Statistical regression analysis showed that NO3 was inversely correlated with relative humidity and positively correlated with temperature and to a lesser extent with NO2 and O3, indicating that the heterogeneous removal processes were also important. The diurnal behavior of NO3 was examined using a one-dimensional chemical transport model. The simulations showed that NO3 trends and concentrations were influenced mainly by changes in ozone and nitrogen oxide levels and that the very high levels of NO3 can be explained by the entrainment of fresh ozone from the upper atmospheric levels. After sunset and in the early morning, the homogeneous processes are the major loss pathways, while the heterogeneous N2O5 removal pathway dominates the intermediate times.

The levels, variation characteristics, and sources of atmospheric non-methane hydrocarbon compounds during wintertime in Beijing, China

“…The relatively high OH concentrations during haze days in winter in Beijing could accelerate oxidation of gas species and further promote formation of secondary particles. The NO 3 concentrations were calculated to be in the range from 2.82 × 10 9 to 4.86 × 10 9 molecules cm −3 on clear days, which were in good agreement with the maximal value (4.92 × 10 9 molecules cm −3 ) reported in Houston during winter (Asaf et al, 2010). It should be mentioned that the OH and NO 3 derived from the propane / propene ratios could only represent their lower limits because of the continued mixing of fresh emissions with the aged air.…”

Mercury Distribution across 14 U.S. Forests. Part II: Patterns of Methyl Mercury Concentrations and Areal Mass of Total and Methyl Mercury

“…A limitation of our estimates of areal mass is that they were standardized to the top 0−40 cm soil depth and do not account for potentially different soil depths; this may not be a major issue given that most Hg is considered to accumulate in surface reservoirs. 7,28 Spatial patterns of atmospheric Hg concentrations and rates of depositionfor example, as assessed by the EPA Toxics Release Inventory for Hg, 50 Hg wet deposition based on National Atmospheric Deposition Program maps, 51 and atmospheric gaseous and oxidized Hg levels and depositions based on models 17 are not known to show latitudinal gradients and, hence, are unlikely to directly cause these south−north gradients. Climate gradients can affect mean residence times of C in soils and terrestrial ecosystems, 52 and this may be linked to observed latitudinal gradients of THg and MeHg concentrations and areal mass.…”

Heterogeneous Atmospheric Chemistry, Ambient Measurements, and Model Calculations of N2O5: A Review

“…One of the dominant NO 3 loss pathways during the day and at the surface at night is the reaction with NO (Wayne et al 1991;Asaf et al 2010):…”