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Holme Moss Long Term Measurements

Long-Term Measurements at Holme Moss
Holme Moss is located in the Southern Pennines close to the top of Black Hill in the Peak District, about 25 km ENE of Manchester City Centre, and at an altitude of 525 m. With the prevailing wind coming from a South Westerly direction, this site often experiences polluted air masses that have passed over Manchester. The site is however relatively remote from any significant local pollution sources (at least in the prevailing wind direction). The measurement site is located inside the transmission mast compound, and facilities consist of a small cabin (upgraded in April 2007), and space for external instruments and additional cabins, etc. for larger projects.

The site has been used for long-term measurements of chemical composition of rain and cloud water (Holme Moss experiences a significant number of days in cloud, especially during the winter months, and so is suitable for ground based cloud measurements) since 1994. Rain and cloud water samples are collected weekly from the site. They are then analysed for concentrations of major ions of anthropogenic (SO42-, NO3-, NH4+, and H+) and marine origin (Na+, Cl-, Ca2+, Mg2+ and K+). In addition, fortnightly samples are sent to the Centre for Ecology & Hydrology (CEH) in Lancaster for heavy metals analysis. An Automatic Weather Station also provides hourly data of wind speed and direction, temperature, relative humidity, solar radiation, rainfall and cloud amount.

The results are interpreted in the light of the effects of the seeder–feeder enhancement and reductions in UK emissions of pollutants. Rainfall volume enhancement is dependent on the spatial and temporal extent of orographic cloud at the site, with resultant consequences on ionic strength in the samples. Large rainfall amounts are associated with longer cloud duration and lower cloud base. Rain passing through the cloud scavenges proportionately more larger droplets, resulting in relatively lower ionic concentration. Coupled with increased washout upwind, this limits the amount of deposition, with some ions showing a decrease in deposition at high rainfall amounts. Clear downward trends are seen in sulphate concentration in rain and cloud water, with both emissions reduction and the dilution effect of increasing rainfall being responsible. Less significant downward trends are observed for nitrate, although this is in line with national patterns of deposition. Deposition at Holme Moss for all ions is dominated by the prevailing, predominantly maritime, southwesterly airflow, although for non-marine ions there are significant contributions from the industrial areas of Yorkshire to the east, and to a lesser extent from the Birmingham conurbation to the south.

Beswick, K.M., Choularton, T.W., Inglis, D.W.F., Dore, A.J., & Fowler, D. (2003) Influences on long-term trends in ion concentration and deposition at Holme Moss. Atmospheric Environment 37, 1927-1940.

Dore, A.J., Choularton, T.W., & Inglis, D.W.F. (2001) Monitoring studies of precipitation and cap cloud chemistry at Holme Moss in the southern Pennines. Water, Soil & Air Pollution: Focus 1, 381-390.

Inglis, D.W.F., Choularton, T.W., & Dunning, B. (2001) Gas and aerosol loadings at Holme Moss 1996-1998, measurements and analysis using back-trajectory clustering. Water, Soil & Air Pollution: Focus 1, 355-364.