Abstract
Here we present measurement results of temporal distributions of nitrous acid (HONO) along with several chemical and meteorological parameters during the spring and the late summer of 2019 at Tudor Hill Marine Atmospheric Observatory in Bermuda. Large temporal variations in HONO concentration were controlled by several factors including local pollutant emissions, air mass interaction with the island, and long-range atmospheric transport of HONO precursors. In polluted plumes emitted from local traffic, power plant and cruise ship emissions, HONO and nitrogen oxides (NOx) existed at substantial levels (up to 278 pptv and 48 ppbv, respectively) and NOx-related reactions played dominant roles in daytime formation of HONO. The lowest concentration of HONO was observed in marine air, with median concentrations at ~3 pptv around solar noon and < 1 pptv during the nighttime. Considerably higher levels of HONO were observed during the day in the low-NOx island-influenced air ([NO2] < 1 ppbv), with a median HONO concentration of ~17 pptv. HONO mixing ratios exhibited distinct diurnal cycles that peaked around solar noon and were lowest before sunrise, indicating the importance of photochemical processes for HONO formation. In clean marine air, NOx-related reactions contributed to ~35 % of the daytime HONO source and the photolysis of particulate nitrate (pNO3) can account for the missing source assuming a moderate enhancement factor of 30 relative to gaseous nitric acid photolysis. In low-NOx island-influenced air, the contribution from both NOx-related reactions and pNO3 photolysis accounted for only ~30 % of the daytime HONO production, and the photochemical processes on surfaces of the island, such as the photolysis of nitric acid on the forest canopy, might contributed significantly to the daytime HONO production. The concentrations of HONO, NOx and pNO3 were lower when the site was dominated by the aged marine air in the summer and were higher when the site was dominated by North American air in the spring, reflecting the effects of long-range transport on the reactive nitrogen chemistry in the background marine environments.
Highlights
Nitrous acid (HONO) is a reactive nitrogen species that plays an important role in the oxidation capacity of the troposphere, as its rapid photolysis (R1) can account for a significant fraction of the production of hydroxyl 45 radical (OH) (Elshorbany et al, 2010, 2012; Kleffmann et al, 2005; Perner and Platt, 1979): !"HONO $% nitrogen oxide (NO) + OH (R1)The chemistry of HONO, especially during the daytime, is not well understood
The readers are referred to the Supplemental Information for detailed calculations of aerosol nitrate photolysis rate constant leading to HONO production J.//0!, which was normalized to light conditions during 200 tropical summer with solar zenith angle of 0°. 3 Results and Discussion Fig. 1 presents an overview for some chemical and meteorological parameters that were measured during the spring and late summer field campaigns of 2019, including HONO, nitrogen oxides (NOx), pNO3, NITs, JHONO, wind speed and wind direction
In order to provide direct comparisons of data based on source regions of air masses, i.e., North American (NA) in the spring and North Atlantic Ocean (NAO) in the summer, we excluded measurement data collected during May 3–7 and September 7–10, and generated whisker plots (Fig. S4) comparing HONO, NOx, pNO3 300 concentrations and HONO/NOx ratios
Summary
Nitrous acid (HONO) is a reactive nitrogen species that plays an important role in the oxidation capacity of the troposphere, as its rapid photolysis (R1) can account for a significant fraction of the production of hydroxyl 45 radical (OH) (Elshorbany et al, 2010, 2012; Kleffmann et al, 2005; Perner and Platt, 1979):. To examine the importance of pNO3 as photolytic HONO source, we collected aerosol samples during the field campaigns and conducted photochemistry experiments to determine the pNO3 photolysis rate constants leading to HONO formation in the gas phase. 2.2 pNO3 Photolysis Rate Constant Determination Bulk aerosol samples were collected on Teflon filters (Sartorius Biolab Products, 0.45 μm pore size, 47 mm diameter) during the field campaigns. The readers are referred to the Supplemental Information for detailed calculations of aerosol nitrate photolysis rate constant leading to HONO production J.//0!, which was normalized to light conditions during 200 tropical summer with solar zenith angle of 0°
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call