Abstract
This work assessed the relationship between synoptic circulation patterns, meteorological conditions and sulfate levels in rainwater in Orizaba Valley, Veracruz, Mexico during 2015. Samples were collected by using an automatic deposition sampler considering three climatic periods: Cold fronts or Nortes, Dry and Rainy seasons. Sulfate in rainwater was determined by turbidimetry (NMX-AA-SCFI-074-1981). A backward trajectory model (HYSPLIT) was used to characterize the potential source regions and transport pathways for air parcels arriving to Orizaba Valley; trajectories extended five days during 2015 were calculated. Mean concentrations of sulfate were 105.33, 37.5, and 52.5 μEq·l-1, for Cold Fronts, Dry and Rainy seasons, respectively. An evident dilution pattern was observed with lower concentration levels when rainfall increased. Mean values for sulfate concentration exceeded the background hemispheric value reported by Galloway et al. (1982) for remote sites (10 μEq·l-1), exceeding almost 10, 3.7 and 5.2 times, during the Nortes, Rainy and Dry seasons, respectively. From the obtained results, it was concluded that the high sulfate levels in the rainwater measured in Orizaba Valley had their origin in different upwind regional sources as a result of long-range transport during Rainy and Nortes seasons.
Highlights
IntroductionBesides of the contribution of local sources, sulfate levels observed in these sites could be improved because of the long-range transport from upwind distant sources during some climatic seasons
During the Cold fronts season a total of62 rain events occur along six months, sulfate levels ranged from 38 to 131 μEq∙l−1, with a mean value of 105.33; whereas during the Dry season, a total of 11 rain events occur along two months, sulfate levels ranged from 18 to 74 μEq∙l−1, with a mean value of 37.5
The highest mean sulfate level was found during the Cold fronts season (Nortes) (105.33 μEq∙l−1) exceeding almost ten times the background hemispheric values reported by Galloway et al [9]; whereas during the Rainy and Dry season, the exceedances were 3.7 and 5.2, respectively
Summary
Besides of the contribution of local sources, sulfate levels observed in these sites could be improved because of the long-range transport from upwind distant sources during some climatic seasons. Mountain-Valley systems can be sensitive to Sulphur pollutants due to their complex topography, and it has been reported that S deposition is major because of emissions released along the pathway of the backward trajectories passing over urban and industrial corridors located upwind, improving in a significant way the background levels of sulfate [2] [3]
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