Aerosol chemical and physical measurements were made at altitudes from 0.27 to 3 km near the coast of southern Nova Scotia, Canada, during the 1993 North Atlantic Regional Experiment. The volume distributions of aerosol with diameters between 0.005 and 3 μm were dominated by accumulation mode particles. The mass and volume ratios (Rm and Rv) of the sum of soluble organics (SumOrg) to non-sea-salt (nss) SO=4 were relatively invariant for estimated total particle mass (TPM) in excess of 13 μg m-3 (high TPM) but increased sharply with decreasing TPM below 13 μg m-3 (low TPM). Overall, the relationships between TPM and Rm and Rv were found to be Rm=-(0.17¿0.44)+(3.5¿1.0)TPM-(0.69¿0.39) and Rv=-(0.35¿0.70)+(5.7¿1.7)TPM-(0.68¿0.39). The high TPM aerosols originated in eastern North America and had average composition of 46% nssSO4-, 8% NH+4, and 8% SumOrg. In contrast, low TPM aerosols were found to be of background continental or marine tropospheric origins and had average composition of 23% nssSO=4, 9% NH+4, and 20% SumOrg. The aerosols in both TPM regimes were separated into two groups based on the mode of the volume distributions. The correlation between the mass of each species and the particle volume distribution was investigated for these groups. ¿ American Geophysical Union 1996