92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Wednesday, 25 January 2012
New Particle Formation (NPF) in a Suburban Mixed-Use Land Zone Site: Statistical Relationships Between Long Range Transport, Aerosol Composition, and Size Distribution
Hall E (New Orleans Convention Center )
Rufus White, Howard Univ., Washington, DC

Poster PDF (1.2 MB)

Background Aerosol particles have profound impacts on human health, local or regional air quality, atmospheric radiation, and climate change and these impacts are strongly dependent on particle sizes. Trace gases, such as sulfur dioxide (SO2), nitric acid (HNO3), and ammonia (NH3), play important roles in aerosol formation. However, formation and growth of atmospheric particles are currently not well understood. A prime motivation for this study was to derive a statistical relationship between meteorological, trace gas, and new particle formation (NPF). Directly measuring the composition of these newly formed particles is extremely difficult. This problem was approached indirectly by observing the different ambient air characteristics and relating the trace gas aerosol meteorologically interdependent behavior, hygroscopicity (water uptake), volatility (evaporation), and particle density to the formation of new particles. In this work, statistical and theoretical studies have been performed to investigate the formation and subsequent growth of atmospheric particles. Methods To assess the microphysics and chemical processes that influence the production of anthropogenic and natural fine aerosols, in a suburban environment simultaneous observation were recorded on aerosol size distribution, inorganic composition, and precursor gas mixing ratios at a suburban field site near Beltsville, MD from June to September 2005. Gas and aerosol samples were taken using two newly developed Monitoring Instruments for Aerosols and Gases (MARGA), which were collocated at the site for comparison. Major water-soluble inorganic ions; nitrate (NO3-), sulfate (SO42-), ammonium (NH4+), precursor gases were analyzed online with a time resolution of one hour for the gas and aerosol phase. To quantify these trace gases during this intensive observation period (IOP) Thermo-Environmental Company (TECO) analyzers (ozone, SO2, NOy, and NOx) were co-located at the site. The MARGA gas measurement was successfully compared to these similar instruments. A laser particle counter (LPC) was also co-located at the site to record aerosol size distribution. Meteorological factors, such as wind speed and direction via NOAA HYSPLIT back trajectories was combined with the MARGA data and used to identify the markers and indicator that can be assigned to the regional pollution sources. PCA was used to confirm the theoretical differences and similarities in the diurnal and local pollution conditions leading to NPF and fine secondary aerosols. Results We identified two unique episodes that were regionally advected air masses were incident to the site with low wind speeds; the first was from August 18, 2005 to August 20, 2005 (Episode A) and the second was from August 23, 2005 to August 25, 2005 (Episode B). Diurnal variations in NO3, SO2, HNO3, and NH3 were observed with maximum concentrations during the day. Maximum sulfate and ammonium mixing ratio was recorded during the night 28.0𝛍g/m3 and 9.90𝛍g/m3, respectively. During Episode A the LPC recorded a maximum TSP count of 1.10 X 107 particles/cm3 and Episode B the LPC recorded a maximum TSP count of 7.45 X 106 particles/cm3. Yet, in 0.3-0.5, 𝛍m size range reached a maximum count of 3.64 X 106 particles/cm3 during latter period and the 0.5-0.7 𝛍m size range reached a maximum count of 5.23 X 106 particles/cm3 during earlier period. The ambient measurements showed that sulfuric acid and sulfate aerosols dominated the new particle formation events. Also, the sulfuric acid/ammonia neutralization reaction product (ammonium sulfate) was detected in ambient air throughout this work. Conclusions The results show the NPF is associated with SO2 oxidation, condensation of volatile gases, and hygroscopic reactions, which are inhibited by the liquid aerosol surface area such that NPF competes with the liquid aerosol surface reactions. This statistical analysis may provide simplified model parameterization which can be used as a part of a larger atmospheric model to predict the concentration of climatically active particles.

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