Contrasted Effects of Relative Humidity and Precipitation on Urban PM2.5 Pollution in High Elevation Urban Areas

Abstract

Levels of urban pollution can be influenced largely by meteorological conditions and the topography of the area. The impact of the relative humidity (RH) on the daily average PM 2.5 concentrations was studied at several sites in a mid-size South American city at a high elevation over the period of nine years. In this work, we show that there is a positive correlation between daily average urban PM 2.5 concentrations and the RH in traffic-busy central areas, and a negative correlation in the outskirts of the city in more industrial areas. While in the traffic sites strong events of precipitation (≥9 mm) played a major role in PM 2.5 pollution removal, in the city outskirts, the PM 2.5 concentrations decreased with increasing RH independently of rain accumulation. Increasing PM 2.5 concentrations are to be expected in any highly motorized city where there is high RH and a lack of strong precipitation, especially in rapidly growing and developing countries with high motorization due to poor fuel quality. Finally, two models, based on a logistic regression algorithm, are proposed to describe the effect of rain and RH on PM 2.5 , when the source of pollution is traffic-based vs. industry-based.

Evidence of Natural and Anthropogenic Impacts on Rainwater Trace Metal Geochemistry in Central Mexico: A Statistical Approach

“…A Pearson correlation matrix (p < 0.05) revealed significant correlations between the meteorological characteristics and total metal burden at each site (Table 3). A positive correlation (r 2 ) of RH vs precipitation in Pachuca (0.92), Molango (0.76), and Agua Blanca (0.66) indicate that high RH is often a predictor of precipitation events [86]. Specifically, Tula presented substantial interrelationships between TMB and WV (r 2 = 0.91), RH (r 2 = −0.90) and BP (r 2 = 0.77).…”

Seasonal variations in PM10 inorganic composition in the Andean city

“…combined with high elevation, contributes to persistent photochemical smog events. Tropical Andean Quito is characterized by a clear definition of rainy (September-May) and dry (June-August) seasons 37 .…”

A Traffic-Based Method to Predict and Map Urban Air Quality

“…This complex terrain city, although characterized by microclimates, has two well-defined seasons. The dry season that lasts from June to August has low precipitation (14 mm/month) and high winds, while the rainy season, from September to May, is characterized by convective precipitation during the afternoon hours (59 mm/month) [28]. Due to its nestling in the Andes cordillera, morning temperature inversions are commonly demonstrated by dark grey smog episodes during morning rush hours.…”

“…This automated Thermo Scientific 5014i Beta Continuous Ambient instrument forms a part of the air quality and meteorological (Vaisala WXT536) monitoring station (Belisario) in the center of the experimental site ( Figure 1c). The background concentrations of PM 2.5 and meteorological data were downloaded from this station, previously described elsewhere [10,28]. The portable PM 2.5 and the GPS equipment were synchronized to function at a 5-s time step.…”