The Chemical Composition of Winter Fogs at São Paulo Highway Sites

Abstract

Radiation and advection fogs were characterized at two sites nearby important roads next to São Paulo City, Brazil. Water-soluble ions, monosaccharides, other sugars and organic and elemental carbon (OC and EC) were determined. Both sites present a high number of fog events with mainly radiation fogs causing visibility problems to the automotive traffic (Castello Branco and Raposo Tavares roads). Samples were collected in nine events in 2009 and ten events in 2010, during wintertime. Two radiation and advection fog events have been herein presented. The radiation fog occurred in 2009 at Castello Branco Road (CBR), presented the highest concentration of pollutants comparing to all other events. The most abundant species are associated with biomass landfill and fossil fuel burning. Locally, the region has a strong impact by the fertilizer industries and traffic of heavy vehicles. The second most polluted event occurred also in 2009 at CBR, an advection fog presented species attributed to soil resuspension and anthropogenic emissions. The results are compared with rainwater composition studies.

The acidity of atmospheric particles and clouds

“…For systems where a single mixed aerosol phase is assumed, current work indicates dissociating organic acids do not strongly affect pH, and the limited studies to date suggest that inorganic species drive pH (Battaglia et al, 2019;Song et al, 2018;Vasilakos et al, 2018). For the southeastern US, pH changes predicted by E-AIM were generally limited to < 0.2 pH units in response to dramatic increases in oxalic acid .…”

“…While the above studies applied different proxies, recent work demonstrates the direct role of aerosol pH in modulating the sulfate-nitrate-ammonium-water aerosol system. Vasilakos et al (2018) demonstrate that nitrate partitioning in response to changing SO 2 emissions also depends on NVCs, which must be properly accounted for to accurately model pH.…”

“…However, the use of the sensitivity indicators has been limited because their robustness has not been well established. Recent work Vasilakos et al, 2018) has begun to explore the influence of particle acidity on the simulated responsiveness of PM 2.5 to emissions changes. Vasilakos et al (2018) demonstrated that reliable predictions of particle pH in CTMs are key to modeling the response of PM 2.5 components to precursor emission changes.…”

“…Recent work Vasilakos et al, 2018) has begun to explore the influence of particle acidity on the simulated responsiveness of PM 2.5 to emissions changes. Vasilakos et al (2018) demonstrated that reliable predictions of particle pH in CTMs are key to modeling the response of PM 2.5 components to precursor emission changes. Furthermore, pH biases may propagate to biases in nitrate partitioning, dissolved metal concentrations, inorganic and organic aerosol amount and composition, and aerosol size distributions and ultimately could affect predicted impacts of emissions on ecosystem productivity and public health.…”

“…Furthermore, meteorology (RH, T ) is an important driver of pH, and meteorological trends influenced by climate change or interannual variability can dominate over any composition changes (Tao and Murphy, 2019b). The eventual response of aerosol pH to changing emissions and meteorology can be determined with models -but careful evaluation of them with in situ data is critical to ensure that they are in the correct acidity regime (e.g., Vasilakos et al, 2018;.…”