Evaluation of the EMEP photo-oxidant model using ozone and meteorological data from Östad, south-west Sweden, for three growing seasons

• This study aimed to evaluate the EMEP photooxidant model by using observations of ozone, air temperature, vapor pressure deficit (VPD) and solar radiation from Östad (Sweden) during three growing seasons, 1997, 1999 and 2000. Also, functions used by the EMEP model to estimate the influences by temperature, VPD and solar radiation on stomatal conductance of crops were applied to observed and modeled data to evaluate the model prediction of stomatal conductance. The results indicated good agreement between model and observations of ozone during daytime, but the nocturnal ozone concentration dropped considerably lower at Östad compared to EMEP model predictions, on average 10 nmol mol-1. The EMEP model tended to overestimate the temperature compared to Östad, especially during the night (3-4°C on average). Large local cooling at night at the monitoring site promoted the generation of temperature inversions and indicated stable atmospheric conditions, which explained the lower nocturnal ozone and temperature compared to the EMEP grid (50*50 km2) values. VPD was overestimated, partly due to overestimation of temperature. The model predicted influence by the meteorological variables on stomatal conductance correlated strongly with predictions based on observed data. Important conclusions from the study were that the EMEP model output correlated well with observed ozone concentration and meteorology at Östad. The differences found were to a large extent due to the specific local climatological conditions at the site, where nocturnal temperature inversions were strong. The synoptic weather situation influenced the agreement between model and observations. Anti-cyclonic weather situations strengthened the differences in local climate between sites within the grid (shown in an earlier study), which led to differences in ozone concentration. During cyclonic weather situations all site specific differences leveled out and the agreement between model and observations was very high. This emphasizes the importance of considering local climate on monitoring sites when evaluating regional air pollution models.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Environmental Sciences (hsv//eng)

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Meteorologi och atmosfärforskning (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Meteorology and Atmospheric Sciences (hsv//eng)

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