Nitrous acid interference with passive NO2 measurement methods and the impact on indoor NO2 data.

Recent research has demonstrated that nitrous acid (HONO) is produced in indoor environments by NO2 reacting with interior surfaces, and is also emitted directly by some combustion sources. We have recently characterized the interference by HONO to NO2 measurements made by several commonly used continuous NO2 monitors. This paper reports on the effect of HONO on NO2 measurements made by passive sampling devices. The objective of this study was to evaluate this interference, and the accuracy and precision of passive samplers used for indoor NO2 measurements. We report that HONO interferes quantitatively with three of the four NO2 passive samplers tested.

The role of Br2 and BrCl in surface ozone destruction at polar sunrise.

Bromine atoms are believed to play a central role in the depletion of surface-level ozone in the Arctic at polar sunrise. Br2, BrCl, and HOBr have been hypothesized as bromine atom precursors, and there is evidence for chlorine atom precursors as well, but these species have not been measured directly. We report here measurements of Br2, BrCl, and Cl2 made using atmospheric pressure chemical ionization-mass spectrometry at Alert, Nunavut, Canada. In addition to Br2 at mixing ratios up to approximately 25 parts per trillion, BrCl was found at levels as high as approximately 35 parts per trillion. Molecular chlorine was not observed, implying that BrCl is the dominant source of chlorine atoms during polar sunrise, consistent with recent modeling studies. Similar formation of bromine compounds and tropospheric ozone destruction may also occur at mid-latitudes but may not be as apparent owing to more efficient mixing in the boundary layer.

Transformations, lifetimes, and sources of NO2, HONO, and HNO3 in indoor environments.

Recent research has demonstrated that nitrogen oxides are transformed to nitrogen acids in indoor environments, and that significant concentrations of nitrous acid are present in indoor air. The purpose of the study reported in this paper has been to investigate the sources, chemical transformations and lifetimes of nitrogen oxides and nitrogen acids under the conditions existing in buildings. An unoccupied single family residence was instrumented for monitoring of NO, NO2, NOy, HONO, HNO3, CO, temperature, relative humidity, and air exchange rate. For some experiments, NO2 and HONO were injected into the house to determine their removal rates and lifetimes. Other experiments investigated the emissions and transformations of nitrogen species from unvented natural gas appliances. We determined that HONO is formed by both direct emissions from combustion processes and reaction of NO2 with surfaces present indoors. Equilibrium considerations influence the relative contributions of these two sources to the indoor burden of HONO. We determined that the lifetimes of trace nitrogen species varied in the order NO approximately HONO > NO2 > HNO3. The lifetimes with respect to reactive processes are on the order of hours for NO and HONO, about an hour for NO2, and 30 minutes or less for HNO3. The rapid removal of NO2 and long lifetime of HONO suggest that HONO may represent a significant fraction of the oxidized nitrogen burden in indoor air.

The distribution of oxidized nitrogen in urban air.

This paper describes the distribution of oxidized nitrogen compounds in urban air. The studies reported here have focused on NO, NO2, PAN and NO-3. These species have been monitored for periods of several weeks at a nmber of locations throughout the U.S.A. Oxidized nitrogen distribution is discussed in terms of the daily patterns of nitrogen pollutant concentrations, the fractional conversion of NOx to products and the diurnal profile of the conversion fraction, and lastly, the contribution of the individual compounds to the overall oxidized nitrogen burden. Site to site variations in the distribution are explained by photochemical conversion, distance between the site and the source region, and the proximity of local NOx emission sources.

Nitrogen oxide reactions in the urban plume of Boston.

The rate of removal or conversion of nitrogen oxides has been determined from airborne measurements in the urban plume of Boston. The average pseudo-first-order rate constant for removal was 0.18 per hour, with a range of 0.14 to 0.24 per hour under daylight conditions for four study days. The removal process is dominated by chemical conversion to nitric acid and organic nitrates. The removal rate suggests an atmospheric lifetime for nitrogen oxides of about 5 to 6 hours in urban air.