ABSTRACT
To scientifically understand the emissions and chemistry of volatile organic compounds (VOCs) in a typical petrochemical industrialized and dust-rich region of Northwest China, VOCs were measured at a receptor site in the Lanzhou Valley using a high-resolution online proton transfer reaction-mass spectrometer (PTR-MS). The ranking of VOC mixing ratios was methanol (32.72⯱â¯8.94â¯ppb)â¯>â¯acetaldehyde (5.05⯱â¯2.4â¯ppb)â¯>â¯acetic acid (3.42⯱â¯1.71â¯ppb). Lanzhou has higher oxygenated VOCs (OVOCs) mixing ratios (methanol and acetaldehyde) and lower aromatics levels (benzene, toluene and C8-aromatics) compared with other cities. The positive matrix factorization (PMF) model showed eight sources of VOCs as follows: (1) mixed industrial process-1 (13.5%), (2) secondary formation (13.2%), (3) mixed industrial process-2 (11.8%), (4) residential biofuel use and waste disposal (13.80%), (5) solvent usage (10.1%), (6) vehicular exhaust (11.8%), (7) biogenic (13.8%) and (8) biomass burning (12.0%). Both the PSCF and the CWT results of mixed industrial process-1 were mainly from the northeast of Lanzhou and the biomass burning was from the southeast; the other four sources (without secondary formation and biogenic) were mainly from the west and northwest of Lanzhou, which were associated with the dust area of the Gobi Desert. A trajectory sector analysis revealed that the local emissions contributed 64.9-71.1% to the VOCs. OVOCs accounted for 43% of the ozone production potential (OFP), and residential biofuel use and waste disposal (25.1%), mixed industrial process-2 (15.3%) and solvent usage (13.4%) appeared to be the dominant sources contributors to O3 production. The rank of main secondary organic aerosols (SOA) precursors under low-NOx conditions is xyleneâ¯>â¯tolueneâ¯>â¯benzeneâ¯>â¯naphthaleneâ¯>â¯styreneâ¯>â¯C10-aromaticsâ¯>â¯isoprene, while under high-NOx conditions, it is tolueneâ¯>â¯naphthaleneâ¯>â¯xyleneâ¯>â¯C10-aromaticsâ¯>â¯styreneâ¯>â¯benzeneâ¯>â¯isoprene. Solvent usage and vehicular exhaust appeared to be the dominant contributors to SOA formation.