aerosols

Speciation of water‐soluble inorganic, organic, and total nitrogen in a background marine environment: Cloud water, rainwater, and aerosol particles

Gioda, A., G. J. Reyes‐Rodríguez, G. Santos‐Figueroa, J. L. Collett Jr., S. Decesari, M. d. C. K. V. Ramos, H. J. C.
Bezerra Netto, F. R. de Aquino Neto, and O. L. Mayol‐Bracero (2011), Speciation of water‐soluble inorganic, organic, and total
nitrogen in a background marine environment: Cloud water, rainwater, and aerosol particles, J. Geophys. Res., 116, D05203,
doi:10.1029/2010JD015010.

Abstract: 
Cloud water, rainwater, and aerosol particles were collected in Puerto Rico from December 2004 to March 2007 in order to investigate their chemical composition, relation to sources, and removal processes. The species analyzed were inorganic ions, metals, total and dissolved organic carbon (TOC, DOC), total nitrogen (TN), and organic acids. For all samples, the dominant species were marine (Na+, Cl−), representing about 50%–65% of total content. Non‐sea‐salt fraction was dominated by SO42− (17%–25%), followed by water‐soluble organic (2%–8%) and total nitrogen (2% –6%) compounds. Organic acids represented contributions to the organic fraction in cloud water of 20% and 6% for aerosol particles. Inorganic species were predominant in total nitrogen portion. The chemical composition of cloud water, rainwater, and aerosol particles were observed to be sensitive to transport patterns. Air masses from northwest Africa showed the highest concentrations of nss‐Ca2+, Fe, and Al, suggesting a crustal origin. The pH values for cloud water and rainwater observed under this transport pattern were higher than background conditions, probably due to the alkalinity associated with nss‐Ca2+. The highest concentrations of Cl− and SO42−, with lower pH, were measured during periods of influence from Soufriere Hills volcano eruptions, most likely due to emitted SO2 and HCl. Air masses from North America had an anthropogenic influence, where levels of nss‐SO42−, TOC, and TN were higher (∼4 times) than in clean air masses. These results suggest that long‐range transport could be an extra source of metals and organic/nitrogen species to the Caribbean region ecosystems.

Clouds and aerosols in Puerto Rico – a new evaluation

Allan, J.D., et al., 2007. Clouds and aerosols in Puerto Rico — a new evaluation. Atmos.
Chem. Phys. Discuss. 7, 12573–12616.

Abstract: 
The influence of aerosols, both natural and anthropogenic, remains a major area of uncertainty when predicting the properties and behaviour of clouds and their influence on climate. In an attempt to better understand warm cloud formation in a tropical 5 marine environment, a period of intensive measurements using some of the latest developments in online instrumentation took place in December 2004 in Puerto Rico. Simultaneous online measurements of aerosol size distributions, composition, hygroscopicity and optical properties were made near the lighthouse of Cape San Juan in the north-eastern corner of the island and at the top of East Peak mountain (1040m 10 a.s.l.), the two sites separated by 17 km. Additional measurements of the cloud droplet residual and interstitial aerosol properties were made at the mountain site, accompanied by measurements of cloud droplet size distributions, liquid water content and the chemical composition of cloud and rain water samples. Both aerosol composition and cloud properties were found to be sensitive to wind 15 sector. Air from the east-northeast (ENE) was mostly free of anthropogenic influences, the submircron fraction being mainly composed of non-sea salt sulphate, while that from the east-southeast (ESE) was found to be moderately influenced by populated islands upwind, adding smaller (<100 nm), externally mixed, carbonaceous particles to the aerosol that increased the number concentrations by over a factor of 3. This 20 change in composition was also accompanied with a reduction in the measured hygroscopicity and fractional cloud activation potential of the aerosol. At the mountain site, the average cloud droplet concentrations increased from 193 to 519 cm−3, median volume diameter decreased from 20 to 14 μm and the liquid water content increased from 0.24 to 0.31 gm−3 when the winds shifted from the ENE to ESE. Larger numbers 25 of interstitial particles were recorded, most notably at sizes greater than 100 nm, which were absent during clean conditions. The average size of the residual particles and concentrations of cloudwater nitrate, sulphate and insoluble material increased during polluted conditions.
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