Drainage enhancement effects on a waterlogged Rhode Island (USA) salt marsh.

Drainage enhancement (e.g., ditch digging, open-marsh water management, runnelling) has long been used to reduce tidal marsh soil waterlogging and surface ponding to promote salt hay production and mosquito control.

An Atmospheric Constraint on the NO2 Dependence of Daytime Near-Surface Nitrous Acid (HONO).

Recent observations suggest a large and unknown daytime source of nitrous acid (HONO) to the atmosphere. Multiple mechanisms have been proposed, many of which involve chemistry that reduces nitrogen dioxide (NO2) on some time scale. To examine the NO2 dependence of the daytime HONO source, we compare weekday and weekend measurements of NO2 and HONO in two U.

Observational insights into aerosol formation from isoprene.

Atmospheric photooxidation of isoprene is an important source of secondary organic aerosol (SOA) and there is increasing evidence that anthropogenic oxidant emissions can enhance this SOA formation. In this work, we use ambient observations of organosulfates formed from isoprene epoxydiols (IEPOX) and methacrylic acid epoxide (MAE) and a broad suite of chemical measurements to investigate the relative importance of nitrogen oxide (NO/NO2) and hydroperoxyl (HO2) SOA formation pathways from isoprene at a forested site in California. In contrast to IEPOX, the calculated production rate of MAE was observed to be independent of temperature.

Insights into secondary organic aerosol formation mechanisms from measured gas/particle partitioning of specific organic tracer compounds.

In situ measurements of organic compounds in both gas and particle phases were made with a thermal desorption aerosol gas chromatography (TAG) instrument. The gas/particle partitioning of phthalic acid, pinonaldehyde, and 6,10,14-trimethyl-2-pentadecanone is discussed in detail to explore secondary organic aerosol (SOA) formation mechanisms. Measured fractions in the particle phase (f(part)) of 6,10,14-trimethyl-2-pentadecanone were similar to those expected from the absorptive gas/particle partitioning theory, suggesting that its partitioning is dominated by absorption processes.

Elucidating secondary organic aerosol from diesel and gasoline vehicles through detailed characterization of organic carbon emissions.

Emissions from gasoline and diesel vehicles are predominant anthropogenic sources of reactive gas-phase organic carbon and key precursors to secondary organic aerosol (SOA) in urban areas. Their relative importance for aerosol formation is a controversial issue with implications for air quality control policy and public health. We characterize the chemical composition, mass distribution, and organic aerosol formation potential of emissions from gasoline and diesel vehicles, and find diesel exhaust is seven times more efficient at forming aerosol than gasoline exhaust.

Ozone deposition to an orange orchard: Partitioning between stomatal and non-stomatal sinks.

Orange trees are widely cultivated in regions with high concentrations of tropospheric ozone. Citrus absorb ozone through their stomata and emit volatile organic compounds (VOC), which, together with soil emissions of NO, contribute to non-stomatal ozone removal. In a Valencia orange orchard in Exeter, California, we used fast sensors and eddy covariance to characterize water and ozone fluxes.