摘要：Photochemical production of NOx and HONO from surface snow can significantly impact the
NOx, OH, and
O3 budgets in the
overlying atmosphere. NOx production is driven by the solar photolysis of
NO3− within or at the surface of snowpacks. HONO, however, is a secondary species
that involves H-atom transfer between natural donors and photogenerated
NO2. Here we investigate the mechanism of HONO generation in snowpacks by exploring how
its emissions respond to on-and-off illumination and temperature cycles, and to the
addition of various snow dopants. The presence of humic substances within or at the
surface of the snowpack significantly enhances, and may be an essential requisite for HONO
production. Emission fluxes of NO, NO2, and HONO from snow surfaces were measured under controlled temperature, ozone
mixing ratio and actinic flux conditions. We used natural mid-latitude surface
snow as the snow substrate. Their combined peak emission fluxes reached up to
~3 × 1010 molecules cm−2 s−1,
~103 times larger than typical emissions from polar snowpacks. Less than 1% of available N was
released in these experiments. We report significant post-irradiation HONO emissions from
the snow. Present results indicate a strong, direct correlation between HONO
emissions and the HULIS (humic-like substances) content of the snow surface.
