Measurements of submicron aerosols in Houston, Texas during the 2009 SHARP field campaign

Abstract

[1] During the field campaign of the Study of Houston Atmospheric Radical Precursors/ Surface-Induced Oxidation of Organics in the Troposphere (SHARP/SOOT) in Houston, Texas, a suite of aerosol instruments was deployed to directly measure a comprehensive set of aerosol properties, including the particle size distribution, effective density, hygroscopicity, and light extinction and scattering coefficients. Those aerosol properties are employed to quantify the mixing state and composition of ambient particles and to gain a better understanding of the formation and transformation of fine particulate matter in this region. During the measurement period, aerosols are often internally mixed, with one peak in the effective density distribution at 1.55 ± 0.07 g cm À3 , consistent with a population composed largely of sulfates and organics. Episodically, a second mode below 1.0 g cm À3 is identified in the effective density distributions, reflecting the presence of freshly emitted black carbon (BC) particles. The measured effective density demonstrates a clear diurnal cycle associated with primary emissions from transportation and photochemical aging, with a minimum during the morning rush hour, increasing from 1.4 to 1.5 g cm À3 on average over 5 h, and remaining nearly constant throughout the afternoon. The average BC concentration derived from light-absorption measurements is 0.31 ± 0.22 μg m À3 , and the average measured particle single scattering albedo is 0.94 ± 0.04. When elevated BC concentrations are observed, typically during the morning rush hours, single scattering albedo decreases, with a smallest measured value of about 0.7. Aerosol hygroscopicity measurements indicate that larger particles (e.g., 400 nm) are more hygroscopic than smaller particles (e.g., 100 nm). The measurements also reveal discernable meteorological impacts on the aerosol properties. After a frontal passage, the average particle effective density decreases, the average BC concentration increases, and the aerosol size distribution is dominated by new particle formation.

Elucidating severe urban haze formation in China

“…4). During the clean period, the measured hygroscopic growth factor and effective density are both indicative of an organic-dominant composition, which is typically less hygroscopic and with a smaller density than the inorganic species (24,25). In contrast, the increased hygroscopicity and effective density during the transition and polluted periods reveal the formation of internally mixed secondary organic and inorganic species, indicating increasing contributions from sulfate and nitrate.…”

“…In contrast, the increased hygroscopicity and effective density during the transition and polluted periods reveal the formation of internally mixed secondary organic and inorganic species, indicating increasing contributions from sulfate and nitrate. Evidently, there is a noticeable absence of the primary aerosol constituents from the hygroscopicity and density measurements during the transition and polluted periods, including black carbon, primary organic aerosols, and mineral dusts, whose hygroscopicity and density characteristics are distinct from those of secondary organics and inorganic salts (24,25). Furthermore, the AMS measurements reveal a nonnegligible mass fraction of ammonium during the transition and polluted periods, which is also likely linked to automobile emissions (30).…”

“…Also, high concentrations of 30-to 100-nm particles are periodically observed during the morning and evening rush hours (Fig. 2A); the timing and size of the elevated aerosols are indicative of primary particle emissions originating from local transportation (24,25). Although primary emissions by local traffic are clearly discernible by the transiently elevated number concentrations and may play a role in maintaining the particle number concentrations during the polluted period, these primary particles do not appreciably alter the particle mass growth.…”

Markedly enhanced absorption and direct radiative forcing of black carbon under polluted urban environments

“…S1), by mimicking the ambient gaseous concentrations without the presence of ambient aerosols but introducing seed BC particles, to evaluate the aging and variation in the particle properties under atmospheric conditions (see Materials and Methods). The experiments were performed during May−June 2009 in Houston and August−October 2013 in Beijing, representative of the typical ambient urban conditions in developed and developing countries, respectively (2,(17)(18)(19).…”

The Impact of Sampling Medium and Environment on Particle Morphology

“…Although some current instrumentation is capable of online analysis of aerosol particles [5][6][7][8][9][10], the aerosol community is heavily reliant on off-line sampling, due to lower costs and a more comprehensive range of particle characterization methods available. Typically, a series of samples are collected during laboratory experiments or field measurements, with several replicates to ensure sufficient statistics.…”